WO2016096046A1

WO2016096046A1 - Measuring brush roll current for determining type of surface

Info

Publication number: WO2016096046A1
Application number: PCT/EP2014/078802
Authority: WO
Inventors: Magnus LINDHE; Petter FORSBERG; Niklas WINDH
Original assignee: Aktiebolaget Electrolux
Priority date: 2014-12-19
Filing date: 2014-12-19
Publication date: 2016-06-23

Abstract

The invention relates to a cleaning device (10) and a method for the cleaning device of detecting a type of a surface (31) over which the cleaning device moves. The method for a cleaning device (10) of detecting a type of a surface (31) over which the cleaning device moves, comprises measuring (S101) a drive current (I_OP) of a rotatable cleaning member (14, 17) configured to remove debris from the surface over which the cleaning device moves, comparing (S102) a value of the measured drive current with at least one predetermined current value associated with a certain type of surface, and determining (S103) if the value of the measured drive current corresponds to the predetermined current value, wherein the surface over which the cleaning device moves is considered to be of said certain type.

Description

MEASURING BRUSH ROLL CURRENT FOR DETERMINING TYPE

OF SURFACE

TECHNICAL FIELD

The invention relates to a cleaning device and a method for the cleaning device of detecting a type of a surface over which the cleaning device moves.

BACKGROUND

In many fields of technology, it is desirable to use robots with an autonomous behaviour such that they freely can move around a space without colliding with possible obstacles. Robotic vacuum cleaners are known in the art, which are equipped with drive means in the form of one or more motors for moving the cleaner across a surface to be cleaned. The robotic vacuum cleaners are further equipped with intelligence in the form of microprocessor(s) and navigation means for causing an autonomous behaviour such that the robotic vacuum cleaners freely can move around and clean a space in the form of e.g. a room. Thus, these prior art robotic vacuum cleaners have the capability of more or less autonomously vacuum cleaning a room in which furniture such as tables and chairs and other obstacles such as walls and stairs are located.

WO 97/ 40734 discloses a robotic vacuum cleaner sensing a current of a rotating brush roller in order to determine brush roller blockage. In case the brush roller current exceeds a threshold value, it is determined that the rotation of the brush roller has been blocked, in which case driving of a brush roller motor is stopped and then the motor is driven in an opposite direction in order to resolve the blockage condition . A blockage condition may arise from the robotic vacuum cleaner moving across a surface comprising soft carpets provided with fringes. Upon movement of the robotic cleaner over such a carpet, the fringes can be brought with the brush to wind up on the roller and, in worst case, to get stuck on the brush or between said brush and the adjacent brush roller housing. This can cause a problem with destroyed carpet fringes or cause damage to the brush roller or the accompanying drive motor in case of blockage.

For a robotic vacuum cleaner, it is important to know which type of surface it traverses (hard floor, tiles, carpets, etc.) for two main reasons: firstly, its dust pickup capacity can be improved by adapting the fan and/ or brush speeds to the particular type of surface it is traversing. Secondly, the wheels of the robotic cleaning device can be expected to slip more on a carpet than on e.g. a parquet floor, and this can be valuable to know for navigation purposes.

SUMMARY

An object of the present invention is to solve, or at least mitigate, this problem in the art and to provide an improved method at a cleaning device of detecting a type of a surface over which the cleaning device moves.

This object is attained in a first aspect of the present invention by a method for a cleaning device of detecting a type of a surface over which the cleaning device moves. The method comprises measuring a drive current of a rotatable cleaning member configured to remove debris from the surface over which the cleaning device moves, comparing a value of the measured drive current with at least one predetermined current value associated with a certain type of surface, and determining if the value of the measured drive current corresponds to the predetermined current value, wherein the surface over which the cleaning device moves is considered to be of said certain type.

This object is attained in a second aspect of the present invention by a cleaning device configured to detect a structure of a surface over which the cleaning device moves. The cleaning device comprises a rotatable cleaning member arranged to remove debris from the surface over which the cleaning device moves, a motor arranged to provide the rotatable cleaning member with a drive current, and a controller arranged to measure the drive current of the rotatable cleaning member. The controller is arranged to compare a value of the measured drive current with at least one predetermined current value associated with a certain type of surface, and to determine if the value of the measured drive current corresponds to the predetermined current value, wherein the surface over which the cleaning device moves is considered to be of said certain type.

Advantageously, as the cleaning device moves over the surface to be cleaned, the controller of the cleaning device measures a drive current required to rotate the rotatable cleaning member, being e.g. a brush roll. Then, a value of the measured drive current is compared with at least one predetermined current value associated with a certain type of surface. For instance, the measured drive current value is compared with a first predetermined threshold value T_L, which threshold value is associated with a type of surface being flat and smooth. Thereafter, the controller determines if the value of the measured drive current corresponds to the predetermined current value, wherein the surface over which the cleaning device is considered to be of said certain type, i.e. flat and smooth surface, such as a parquet floor. For instance, the measured drive current value may be considered to correspond with the predetermined value if it is below the threshold value T_L.

For a cleaning device, as previously mentioned, it is important to know which type of surface it traverses (hard floor, tiles, carpets, etc.) for two main reasons: firstly, its dust pickup capacity can be improved by adapting the fan and/ or brush speeds to the particular type of surface it is traversing.

Secondly, the wheels of a cleaning device in the form of a robotic cleaning device can be expected to slip more on a carpet than on e.g. a parquet floor, and this can be valuable to know for navigation purposes.

By using the method according to embodiments of the present invention, a low cost alternative is provided for detecting a type of a surface over which the cleaning device moves. Typically, the drive current of the rotatable cleaning member is measured anyway for diagnostic purposes.

Preferred embodiment of the present invention will be described in the following. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein . All references to "a/ an/ the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DES CRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a bottom view of a robotic cleaning device according to embodiments of the present invention;

Figure 2 shows a front view of the robotic cleaning device illustrated in Figure l; Figure 3a shows a robotic cleaning device implementing the method according to an embodiment of the present invention ;

Figure 3b illustrates a flow chart of an embodiment of the method according to the present invention;

Figure 4 shows a robotic cleaning device implementing the method according to another embodiment of the present invention ;

Figure 5 shows a robotic cleaning device implementing the method according to yet another embodiment of the present invention; and

Figure 6 illustrates a robotic cleaning device traversing various types of surfaces according to an embodiment of the present invention. DETAILED DES CRIPTION OF THE INVENTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein ; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description .

Figure 1 shows a robotic vacuum cleaner in which the present application can be implemented. However, it should be noted that the present invention may be implemented in any vacuum cleaner utilizing a rotating cleaning member in the form of a brush roll or a side brush, such as an upright cleaner, a canister cleaner, a cyclonic vacuum cleaner, a hand-held cleaner, etc., where the robotic cleaner of Figure 1 is an example. The robotic vacuum cleaner can be mains-operated and have a cord, be battery-operated or use any other kind of suitable energy source, for example solar energy. The present invention can further be implemented in other cleaning devices, e.g. a robotic sweeper or a robotic floor washer, both automatic, self- propelled machines for cleaning a surface and manually operated devices.

Figure 1 illustrates a robotic cleaning device 10 according to an embodiment of the present invention, where the bottom side of the robotic cleaning device is shown . The arrow indicates the forward direction of the robotic cleaning device. The robotic cleaning device 10 comprises a main body 11 housing components such as a propulsion system comprising driving means in the form of two electric wheel motors 15a, 15b for enabling movement of the driving wheels 12, 13 such that the cleaning device can be moved over a surface to be cleaned. Each wheel motor 15a, 15b is capable of controlling the respective driving wheel 12, 13 to rotate independently of each other in order to move the robotic cleaning device 10 across the surface to be cleaned. A number of different driving wheel arrangements, as well as various wheel motor arrangements, can be envisaged. It should be noted that the robotic cleaning device may have any appropriate shape, such as a device having a more traditional circular-shaped main body, or a triangular-shaped main body. As an alternative, a track propulsion system may be used or even a hovercraft propulsion system . The propulsion system may further be arranged to cause the robotic cleaning device 10 to perform any one or more of a yaw, pitch, translation or roll movement. A controller 16 such as a microprocessor controls the wheel motors 15a, 15b to rotate the driving wheels 12, 13 as required in view of information received from an obstacle detecting device (not shown in Figure 1) for detecting obstacles in the form of walls, floor lamps, table legs, around which the robotic cleaning device must navigate. The obstacle detecting device may be embodied in the form of a 3D sensor system registering its surroundings, implemented by means of e.g. a 3D camera, a camera in combination with lasers, a laser scanner, etc. for detecting obstacles and communicating information about any detected obstacle to the microprocessor 16. The microprocessor 16 communicates with the wheel motors 15a, 15b to control movement of the wheels 12, 13 in accordance with information provided by the obstacle detecting device such that the robotic cleaning device 10 can move as desired across the surface to be cleaned. This will be described in more detail with reference to subsequent drawings.

Further, the main body 11 is arranged with a cleaning member 17 for removing debris and dust from the surface to be cleaned in the form of a rotatable brush roll arranged in an opening 18 at the bottom of the robotic cleaner 10. Thus, the rotatable brush roll 17 is arranged along a horizontal axis in the opening 18 to enhance the dust and debris collecting properties of the cleaning device 10. In order to rotate the brush roll 17, a brush roll motor 19 is operatively coupled to the brush roll to control its rotation in line with instructions received from the controller 16. The controller 16 can further measure the rotational speed of the brush roll.

Moreover, the main body 11 of the robotic cleaner 10 comprises a suction fan 20 creating an air flow for transporting debris to a dust bag or cyclone arrangement (not shown) housed in the main body via the opening 18 in the bottom side of the main body 11. The suction fan 20 is driven by a fan motor 21 communicatively connected to the controller 16 from which the fan motor 21 receives instructions for controlling the suction fan 20.

The main body 11 or the robotic cleaning device 10 is further equipped with an angle-measuring device 24, such as e.g. a gyroscope 24 and/ or an accelerometer or any other appropriate device for measuring orientation of the robotic cleaning device 10. A three-axis gyroscope is capable of measuring rotational velocity in a roll, pitch and yaw movement of the robotic cleaning device 10. A three-axis accelerometer is capable of measuring acceleration in all directions, which is mainly used to determine whether the robotic cleaning device is bumped or lifted or if it is stuck (i.e. not moving even though the wheels are turning). The robotic cleaning device 10 further comprises encoders (not shown in Figure 1) on each drive wheel 12, 13 which generate pulses when the wheels turn. The encoders may for instance be magnetic or optical. By counting the pulses at the controller 16, the speed of each wheel 12, 13 can be determined. By combining wheel speed readings with gyroscope information, the controller 16 can perform so called dead reckoning to determine position and heading of the cleaning device 10.

The main body 11 may further be arranged with a rotating side brush 14 adjacent to the opening 18 , the rotation of which could be controlled by the drive motors 15a, 15b, the brush roll motor 19, or alternatively a separate side brush motor (not shown). Advantageously, the rotating side brush 14 sweeps debris and dust such from the surface to be cleaned such that the debris ends up under the main body 11 at the opening 18 and thus can be transported to a dust chamber of the robotic cleaning device. Further advantageous is that the reach of the robotic cleaning device 10 will be improved, and e.g. corners and areas where a floor meets a wall are much more effectively cleaned. As is illustrated in Figure 1, the rotating side brush 14 rotates in a direction such that it sweeps debris towards the opening 18 such that the suction fan 20 can transport the debris to a dust chamber. The robotic cleaning device 10 may comprise two rotating side brushes arranged laterally on each side of, and adjacent to, the opening 18. With further reference to Figure 1, the controller/ processing unit 16 embodied in the form of one or more microprocessors is arranged to execute a computer program 25 downloaded to a suitable storage medium 26 associated with the microprocessor, such as a Random Access Memory (RAM), a Flash memory or a hard disk drive. The controller 16 is arranged to carry out a method according to embodiments of the present invention when the appropriate computer program 25 comprising computer-executable instructions is downloaded to the storage medium 26 and executed by the controller 16. The storage medium 26 may also be a computer program product comprising the computer program 25. Alternatively, the computer program 25 may be transferred to the storage medium 26 by means of a suitable computer program product, such as a digital versatile disc (DVD), compact disc (CD) or a memory stick. As a further alternative, the computer program 25 may be downloaded to the storage medium 26 over a network. The controller 16 may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field- programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

Figure 2 shows a front view of the robotic cleaning device 10 of Figure 1 in an embodiment of the present invention illustrating the previously mentioned obstacle detecting device in the form of a 3D sensor system 22 comprising at least a camera 23 and a first and a second line laser 27, 28 , which may be horizontally or vertically oriented line lasers. Further shown is the controller 16, the main body 11, the driving wheels 12, 13, and the rotatable brush roll 17 previously discussed with reference to Figure la. The controller 16 is operatively coupled to the camera 23 for recording images of a vicinity of the robotic cleaning device 10. The first and second line lasers 27, 28 may preferably be vertical line lasers and are arranged lateral of the camera 23 and configured to illuminate a height and a width that is greater than the height and width of the robotic cleaning device 10. Further, the angle of the field of view of the camera 23 is preferably smaller than the space illuminated by the first and second line lasers 27, 28. The camera 23 is controlled by the controller 16 to capture and record a plurality of images per second. Data from the images is extracted by the controller 16 and the data is typically saved in the memory 26 along with the computer program 25.

The first and second line lasers 27, 28 are typically arranged on a respective side of the camera 23 along an axis being perpendicular to an optical axis of the camera. Further, the line lasers 27, 28 are directed such that their respective laser beams intersect within the field of view of the camera 23. Typically, the intersection coincides with the optical axis of the camera 23.

The first and second line laser 27, 28 are configured to scan, preferably in a vertical orientation, the vicinity of the robotic cleaning device 10 , normally in the direction of movement of the robotic cleaning device 10. The first and second line lasers 27, 28 are configured to send out laser beams, which illuminate furniture, walls and other objects of e.g. a room to be cleaned. The camera 23 is controlled by the controller 16 to capture and record images from which the controller 16 creates a representation or layout of the surroundings that the robotic cleaning device 10 is operating in, by extracting features from the images and by measuring the distance covered by the robotic cleaning device 10 , while the robotic cleaning device 10 is moving across the surface to be cleaned. Thus, the controller 16 derives positional data of the robotic cleaning device 10 with respect to the surface to be cleaned from the recorded images, generates a 3D representation of the surroundings from the derived positional data and controls the driving motors 15a, 15b to move the robotic cleaning device across the surface to be cleaned in accordance with the generated 3D representation and navigation information supplied to the robotic cleaning device 10 such that the surface to be cleaned can be navigated by taking into account the generated 3D representation. Since the derived positional data will serve as a foundation for the navigation of the robotic cleaning device, it is important that the positioning is correct; the robotic device will otherwise navigate according to a "map" of its surroundings that is misleading. The 3D representation generated from the images recorded by the 3D sensor system 22 thus facilitates detection of obstacles in the form of walls, floor lamps, table legs, around which the robotic cleaning device must navigate as well as rugs, carpets, doorsteps, etc., that the robotic cleaning device 10 must traverse. The robotic cleaning device 10 is hence configured to learn about its environment or surroundings by operating/ cleaning.

With reference to Figure 2, for illustrational purposes, the 3D sensor system 22 is separated from the main body 11 of the robotic cleaning device 10.

However, in a practical implementation, the 3D sensor system 22 is preferably integrated with the main body 11 of the robotic cleaning device 10 to minimize the height of the robotic cleaning device 10 , thereby allowing it to pass under obstacles, such as e.g. a sofa.

Hence, the 3D sensor system 22 comprising the camera 23 and the first and second vertical line lasers 27, 28 is arranged to record images of a vicinity of the robotic cleaning from which objects/ obstacles may be detected. The controller 16 is capable of positioning the robotic cleaning device 10 with respect to the detected obstacles and hence a surface to be cleaned by deriving positional data from the recorded images. From the positioning, the controller 16 controls movement of the robotic cleaning device 10 by means of controlling the wheels 12, 13 via the wheel drive motors 15a, 15b, across the surface to be cleaned.

The derived positional data facilitates control of the movement of the robotic cleaning device 10 such that cleaning device can be navigated to move very close to an object, and to move closely around the object to remove debris from the surface on which the object is located. Hence, the derived positional data is utilized to move flush against the object, being e.g. a thick rug or a wall. Typically, the controller 16 continuously generates and transfers control signals to the drive wheels 12, 13 via the drive motors 15a, 15b such that the robotic cleaning device 10 is navigated close to the object. Figure 3a illustrates detection of a type of surface 31 over which the robotic cleaning device 10 moves in accordance with an embodiment of the present invention . Reference is further made to Figure 1 for structural elements. In this exemplifying embodiment, the surface 31 over which the robot 10 moves is a flat and smooth surface, such as a parquet floor or a piece of linoleum. Now, in case of the surface 31 being a smooth floor, friction caused between the rotatable brush roll 17 and the smooth floor is low and the drive current provided by the brush roll motor 19 to rotate the brush roll 17 is low.

Figure 3b illustrates a flowchart of the method of detecting a structure of a surface over which the robotic cleaning device moves in accordance with an embodiment of the present invention . In a first step S10 1, a drive current required to rotate the brush roll 17 is measured, for instance by the controller 16. Then, in step S102 a value of the measured drive current is compared with at least one predetermined current value associated with a first type of surface. For instance, the measured drive current value is compared with a first predetermined threshold value T_L, which threshold value is associated with a type of surface being flat and smooth. In another example, the measured drive current value is compared with a predetermined current range being associated with a type of surface being flat and smooth, for instance a range from zero to TL.

In step S 103, it is determined if the value of the measured drive current corresponds to the predetermined current value, wherein the surface 31 over which the cleaning device is considered to be of the first type, i.e. flat and smooth, such as a parquet floor. For instance, the measured drive current value is considered to correspond with the predetermined value if it is below the threshold value T_L.

Advantageously, by determining the structure of the surface 31 over which the robot 10 moves, a number of aspects of the cleaning can be improved. For instance, if the robotic device 10 moves over a flat and smooth surface 31 such as a parquet floor, the suction fan 20 can be driven with a lower operating current, and the brush roll 17 and/ or the side brush 14 can typically be driven to rotate with at a lower rotational speed, thereby extending time periods between robotic device battery charging. Another advantage is that noise is reduced if one or more of the motors can be operated at lower speed.

In a further example, it can be envisaged that the fan 20 is operated at full speed regardless of whether the surface 31 comprise s a hard floor or carpet. However, on hard floor it may be advantageous to lower the rotational speed of the brush roll 17 to avoid having the brush roll 17 push away debris such as rice, cereals, bread crumbs, etc.

Further advantageous is that movement of the robotic device 10 may be controlled depending on the structure of the surface; for instance, if the robotic device 10 moves over a carpet, it may be driven at a lower speed to prevent slipping and/ or go over the carpet, or at least parts of the carpet, more than once. In another example, the robotic device 10 may in a cleaning programme select to go over a section of the floor where a carpet is located as a last step of the programme.

Further, if the robotic cleaner 10 moves over a carpet, the wheels may slip and navigation decisions can as a result be based more on input from other sensors (lasers, gyros, accelerometers, etc.) considered more reliable when the robotic cleaner 10 moves over a carpet. Figure 4 illustrates detection of a type of surface over which the robotic cleaning device 10 moves in accordance with another embodiment of the present invention. In this embodiment, the surface 31 to be cleaned comprises a thin carpet 38 having a structured upper side.

As in the case of the method described with reference to Figure 3b, a drive current required to rotate the brush roll 17 is measured in step S10 1. Then, in step S102 a value of the measured drive current is compared with at least one predetermined current value associated with a second type of surface. For instance, the measured drive current value is compared with a second predetermined threshold value T_M being higher than the previously described first threshold value T_L, which second threshold value T_M is associated with a type of surface being slightly structured, i.e. the carpet 38. In another example, the measured drive current value is compared with a predetermined current range, for instance a range defined by endpoints T_L - T_M, being associated with a type of surface being slightly structured. In step S 103, it is determined if the value of the measured drive current corresponds to the predetermined current value, wherein the surface 31 over which the cleaning device is considered to be of the second type associated with the predetermined current value , i.e. it is considered to comprise the thin and structured carpet 38. In this particular embodiment, by advantageously determining that a structured carpet is to be traversed by the robotic device 10 , it may be necessary to supply the suction fan 20 with a greater operating current, and to rotate the brush roll 17 and/ or the side brush 14 at a higher rotational speed. Further, it may be necessary to go over the carpet more than once as compared to a flat and smooth surface.

Figure 5 illustrates detection of a type of surface over which the robotic cleaning device 10 moves in accordance with still another embodiment of the present invention. In this embodiment, the surface 31 to be cleaned comprises a thick carpet 39, e.g. a rug, provided with a great number of fringes 40 a length of which may be up to 10 cm.

Thus, as in the case of the method described with reference to Figure 3b, a drive current required to rotate the brush roll 17 is measured in step S 10 1 by the controller 16. Then, in step S102 a value of the measured drive current is compared with at least one predetermined current value associated with a third type of surface. For instance, the measured drive current value is compared with a third predetermined threshold value T_H being higher than the previously described first threshold value T_L as well as the first threshold value T_M, which third threshold value T_H is associated with a third type of surface being ragged and typically comprises pieces of fibrous material 40 extending from the rug. Again, in step S 103, it is determined if the value of the measured drive current corresponds to the predetermined current value, wherein the surface 31 over which the cleaning device is considered to be of the third type associated with the predetermined current value , i.e. it is concluded to comprise the thick and ragged carpet 39.

In this particular embodiment, by advantageously determining that a structured carpet is to be traversed by the robotic device 10 , it may be necessary to supply the suction fan 20 with a greater operating current, and to rotate the brush roll 17 and/ or the side brush 14 at a higher rotational speed. Further, it may be necessary to go over the carpet more than once as compared to a flat and smooth surface.

As previously mentioned, it may be necessary to supply the suction fan 20 with a greater operating current, and to rotate the brush roll 17 and/ or the side brush 14 at an even higher rotational speed. Further, it may be necessary to go over the carpet more than once. Moreover, when the robotic device 10 moves over a thick rug 39, it may be subject to so called slip, i.e. the wheels of the robot are turning, but the robot is not moving (or not moving to an extent as expected by the turn of the wheels). When utilizing dead reckoning, as previously has been discussed, wheel speed readings are combining with gyroscope information, and the controller 16 can determine position and heading of the robotic device 10. This is a known method where a current position is calculated by using locational data pertaining to a previously determined position . Thus, the expected slip of the wheels 12, 13 when the robotic device 10 traverses the rug 39 can advantageously be taken into account when determining the position and heading. The controller 16 can as a result advantageously predict the position of the robot 10 with greater accuracy and adapt the driving pattern in order to avoid building up excessive errors in the position estimate.

Figure 6 illustrates an embodiment of the present invention, where the robotic device 10 moves over all three surface types shown in Figures 3a, 4 and 5. Initially, the robotic device 10 moves by means of driving wheel 13 over the surface 31 being a flat and smooth surface such as a parquet floor. As the robotic cleaning device 10 moves over the surface 31 to be cleaned, the process 16 measures a an operating current lop of the brush roll motor 19 required to drive the brush roll 17. As can be seen in the graph illustrating the drive current IO_P as a function of the robotic device 10 moving over the surface 31, the drive current is below the first threshold value T_L, thereby indicating that the surface 31 is of a first type associated with the first threshold value T_L, in this particular exemplifying embodiment a flat and smooth surface. As previously discussed, this may imply a first cleaning programme selected by the controller 16 in the form of e.g. a certain rotational speed of the brush roll 17.

Now, as the robotic device 10 proceeds, it encounters and traverses the thin, structured carpet 38. The current IO_P of the motor 19 required to rotate the brush roll 19, as measured by the controller 16, will increase as the friction of the carpet 38 is higher than that of the parquet floor, thereby requiring a higher brush roll drive current IO_P. The current increases to a value just under the second threshold value T_M (but over the first threshold T_L), thereby indicating that the surface 31 is of a second type associated with the second threshold value T_M, in this particular exemplifying embodiment a thin and structured carpet 38. Again, this may imply a second cleaning programme selected by the controller 16 in the form of e.g. an increased suction fan speed to remove debris stuck on the carpet 38.

Then, the robotic device 10 again encounters the parquet floor 31 as indicated by the brush roll drive current IO_P decreasing under the first threshold value T_L.

Thereafter, the robotic device 10 approaches the thick and ragged rug 39 having fringes 40 extending from its surface. The current increases to a value just under the third threshold value T_H (but over the second threshold T_M) , thereby indicating that the surface 31 is of a third type associated with the third threshold value T_H, in this particular exemplifying embodiment a thick rug 39. This may imply a third cleaning programme selected by the controller 16 in the form of e.g. an instruction to go over the rug 39 more than once to ensure that all debris is removed. Alternatively, the surface 31 may be considered to comprise the thick rug 39 as soon as the measured brush roll drive current IOP exceeds the second threshold value TM.

Finally, the robotic device 10 approaches the parquet floor 31 as indicated by the brush roll drive current IO_P falling under the first threshold value T_L.

As has been illustrated throughout the described embodiments of the present invention, the type of the surface 31 traversed by the robotic cleaning device 10 is determined by measuring a drive current IO_P of the rotatable brush roll 17. However, in an alternative embodiment, the drive current of the side brush 14 is measured in order to determine the type of surface over which the robotic device 10 moves.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A method for a cleaning device ( 10 ) of detecting a type of a surface (3 1) over which the cleaning device ( 10 ) moves, comprising:

measuring (S 10 1) a drive current (IO_P) of a rotatable cleaning member ( 14, 17) configured to remove debris from the surface (3 1) over which the cleaning device ( 10 ) moves;

comparing (S 102) a value of the measured drive current (IO_P) with at least one predetermined current value associated with a certain type of surface; and

determining (S 103 ) if the value of the measured drive current (IOP) corresponds to the predetermined current value, wherein the surface (3 1) over which the cleaning device ( 10 ) moves is considered to be of said certain type.

2. The method of claim 1, wherein in case the measured drive current (IO_P) is below a first predetermined threshold current value (T_L) , the surface (3 1) is determined to comprise a flat floor.

3. The method of claims 1 or 2, wherein in case the measured drive current (IOP) is below a second predetermined threshold current value (TM) , the surface (3 1) is determined to comprise a carpet (38 ) having a structured upper side.

4. The method of any one of claims 1-3 , wherein in case the measured drive current (IO_P) is below a third predetermined threshold current value (TH) , the surface (3 1) is determined to comprise a rug (39) .

5. The method of any one of the preceding claims, further comprising: controlling operation of the cleaning device ( 10 ) based on the

determined type of surface (3 1) .

6. The method of claim 6 , wherein the controlling of the operation of the cleaning device ( 10 ) comprises:

controlling any one or more of suction capacity of a cleaning device suction fan (20), rotational speed of the rotatable cleaning member (17), or movement of the cleaning device (10) over the surface (31).

7. Cleaning device (10) configured to detect a structure of a surface (31) over which the cleaning device moves, comprising:

a rotatable cleaning member (14, 17) arranged to remove debris from the surface (31) over winch the cleaning device (10) moves;

a motor (19) arranged to provide the rotatable cleaning member (14, 17) with a drive current (IOP); and

a controller (16) arranged to measure the drive current (IOP) of the rotatable cleaning member (17); wherein

the controller is arranged to compare a value of the measured drive current (lor) with at least one predetermined current value associated with a certain type of surface, and to determine if the value of the measured drive current (lor) corresponds to the predetermined current value, wherein the surface (31) over which the deaning device (10) moves is considered to be of said certain type.

8. "The deaning device (10) of claim 7, Wherein in case the measured drive current (I_OP) is below a first predetermined threshold current value (Τιλ the surface (31) is determined to comprise a flat floor.

9. The cleaning device (10) of claims 7 or 8, wherein in case the measured drive current (I_OP) is below a second predetermined threshold current value (T_M), the surface (31) is determined to comprise a carpet (38) having a structured upper side,

10. The cleaning device (10) of any one of claims 7-9, wherein in case the measured drive current (Iop) is below a third predetermined threshold current value (T_H), the surface (31) is determined to comprise a rug (39).

11. The cleaning device (10) of any one of claims 7-10, the controller (16) further being arranged to:

control operation of the deaning device (10) based on the determined type of surface (31).

12. The deaning device (10) of daim 11, wherein the controller (16) is arranged to:

control any one or more of suction capacity of a deaning device suction fan (20), rotational speed of the rotatable cleaning member (14, 17), or a propulsion system (12, 13, 15a, 15b) arranged to move the cleaning device (10) over the surface (31).

13. The cleaning device (10) of any one of claims 7-12, the rotatable cleaning member being a rotatable brush roll (17) or a rotatable side brush (14)·

14. The cleaning device (10) of any one of claims 7-13, the cleaning device being any one of a robotic vacuum cleaner, a robotic sweeper, robotic floor washer, an upright vacuum cleaner, a canister vacuum cleaner, a hand-held vacuum cleaner, a cyclonic vacuum cleaner.

15. A computer program (25) comprising computer-executable instructions for causing a device (10) to perform the steps recited in any one of claims 1-6 when the computer-executable instructions are executed on a controller (16) included in the device.

16. A computer program product comprising a computer readable medium (26), the computer readable medium having the computer program (25) according to claim 15 embodied therein.