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Title:
A CONCRETE SURFACE PROCESSING SYSTEM WITH A PERIMETER ACCESS CONTROL SYSTEM
Document Type and Number:
WIPO Patent Application WO/2022/154731
Kind Code:
A1
Abstract:
A concrete surface processing system (100), comprising a mobile perimeter access control arrangement (110, 111, 120, 130) and a concrete surface processing machine (140) arranged for autonomous or remote controlled processing of a concrete surface (101), the mobile perimeter access control arrangement comprising a perimeter access control unit (111) connected to one or more light curtain devices (110, 120, 130) arranged to define a perimeter access controlled area (150) of the concrete surface (101), wherein at least one of the light curtain devices comprises a surface support arrangement (210) configured to support the light curtain device movably on the concrete surface (101), where the concrete surface processing machine (140) comprises a machine control unit (101) arranged to perform an emergency operation in response to receiving a wireless control signal (112), and where the perimeter access control unit (111) is configured to transmit the wireless control signal (112) in response to detecting a perimeter breach by the one or more light curtain devices (110, 120, 130).

Inventors:
HALLBERG EMMA (SE)
LARHED FABIAN (SE)
OTTOSSON LINUS (SE)
ENGMAN ERIK (SE)
GUSTAVSSON DANIEL (SE)
Application Number:
PCT/SE2022/050031
Publication Date:
July 21, 2022
Filing Date:
January 13, 2022
Export Citation:
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Assignee:
HUSQVARNA AB (SE)
International Classes:
B24B7/18; B23Q11/00; B24B55/00; F16P3/14; G01V8/20; E04F21/24; G01S17/04; G08B13/183
Domestic Patent References:
WO2020102458A12020-05-22
Foreign References:
US20040022581A12004-02-05
CN211549010U2020-09-22
DE102009031226A12011-01-05
AU2017261633A12018-06-07
Other References:
"Safety Light Curtains, Photoelectric Safety Switches", SICK AG, 12 September 2018 (2018-09-12), pages 7, 16, 19, 22 - 23, 66-68, 70
Download PDF:
Claims:
27

CLAIMS

1 . A concrete surface processing system (100), comprising a mobile perimeter access control arrangement (110, 1 1 1 , 120, 130) and a concrete surface processing machine (140) arranged for autonomous or remote controlled processing of a concrete surface (101 ), the mobile perimeter access control arrangement comprising a perimeter access control unit (1 11 ) and one or more light curtain devices (110, 120, 130) arranged to define a perimeter access controlled area (150) of the concrete surface (101 ), where the perimeter access control unit (1 11 ) is connected to the one or more light curtain devices (1 10, 120, 130), wherein at least one of the light curtain devices comprises a surface support arrangement (210) configured to support the light curtain device movably on the concrete surface (101 ), where the concrete surface processing machine (140) comprises a machine control unit (101 ) arranged to perform an emergency operation in response to receiving a wireless control signal (1 12), and where the perimeter access control unit (1 11 ) is configured to transmit the wireless control signal (1 12) in response to detecting a perimeter breach by the one or more light curtain devices (1 10, 120, 130).

2. A method for processing at least a part of a concrete surface (101 ), the method comprising deploying (S1 ) one or more mobile light curtain devices (1 10, 120, 130) arranged to define a perimeter access controlled area (150) of the concrete surface (101 ), wherein at least one of the mobile light curtain devices comprises a surface support arrangement (210) configured to support the light curtain device movably on the concrete surface (101 ), deploying (S2) at least one autonomous or remote controlled concrete surface processing machine (140) within the perimeter access controlled area (150), processing (S3) the perimeter access controlled area (150) by the at least one machine (140), and executing (S4) an emergency operation by one or more of the machines (140) in response to detecting a perimeter breach by the one or more light curtain devices (110, 120, 130).

3. A mobile light curtain device (1 10, 120, 130) arranged to define a perimeter access controlled area (150) of a concrete surface (101 ), the light curtain device comprising any of a focused light source (310) for generating a beam of light (160), at least one photo detector (410) for detecting a beam of light (160), and/or at least one mirror (510) for reflecting an incoming beam of light (160) in a predetermined direction, wherein the beam of light (160) is arranged to, if obstructed, indicate a perimeter breach of the perimeter access controlled area (150) of the concrete surface (101 ), the light curtain device also comprising a surface support arrangement (210) configured to support the light curtain device movably on the concrete surface (101 ).

4. The light curtain device (120, 130) according to claim 3, arranged to reflect and/or to receive the beam of light (160), wherein the light curtain device comprises means for detecting rotation angle (£) alignment error of the light curtain device about an axis (A) normal to the concrete surface (101 ) with respect to the beam of light (160).

5. The light curtain device (1 10, 120, 130) according to claim 3 or 4, wherein the surface support arrangement (210) comprises one or more foldable legs (710) arranged around a central supporting foot (720).

6. The light curtain device (1 10, 120, 130) according to claim 3 or 4, wherein the surface support arrangement (210) comprises a supporting plate (810) configured to fit snugly in a corner (1000).

7. The light curtain device (1 10, 120, 130) according to any of claims 3-6, where the surface support arrangement (210) is configured to receive and to hold one or more weights (910) for weighting down the light curtain device against the concrete surface (101 ).

8. The light curtain device (1 10, 120, 130) according to any of claims 3-7, where the surface support arrangement (210) comprises one or more integrated wheels (320) arranged to support the light curtain device on the concrete surface (101 ) in a transport mode of the light curtain device.

9. The light curtain device (1 10, 120, 130) according to any of claims 3-8, comprising a handle (330) arranged to allow an operator to lift the light curtain device from the concrete surface (101 ) and carry the light curtain device.

10. The light curtain device (1 10, 120, 130) according to any of claims 3-9, comprising an integrated spirit level configured to indicate a pose of the light curtain device relative to a horizontal plane.

11 . The light curtain device (1 10, 120, 130) according to any of claims 3-10, comprising a status indicator light (440) arranged visible from a location distant from the light curtain device.

12. The light curtain device (1 10, 120, 130) according to claim 1 1 , wherein the status indicator light (440) is arranged integrated with a handle (330) on the light curtain device.

13. The light curtain device (1 10, 120, 130) according to any of claims 3-12, where a light curtain device body section (420) is attached to the surface support arrangement (210) by a ball joint (430).

14. The light curtain device (1 10, 120, 130) according to claim 13, where the ball joint (430) is a lockable ball joint.

15. The light curtain device (1 10, 120, 130) according to claim 14, where the lockable ball joint is arranged to be released by a pedal mechanism (610) biased towards a locked position of the ball joint, wherein the ball joint is arranged to be released from the locked position by depressing the pedal mechanism.

16. The light curtain device (1 10, 120, 130) according to any of claims 3-15, comprising an extendable distance measuring member configured to indicate a maximum separation distance with respect to a distant light curtain device.

17. The light curtain device (1 10, 120, 130) according to any of claims 3-16, where the surface support arrangement (210) comprises at least one levelling mount (340) configured to adjust an angle of the surface support arrangement (210) relative to a supporting concrete surface.

18. The light curtain device (1 10, 120, 130) according to claim 4, wherein the means for detecting rotation angle (£) alignment error comprises an elongated straight passage (1210) terminated by a surface (1220), configured to allow a light beam (1230) from a distant guiding light source (1310) to traverse the passage and illuminate the surface from a predetermined range of angles, wherein the passage has a width measured perpendicular to the passage direction (D) of the beam of light smaller than an extension length (L) of the passage.

19. The light curtain device (1 10, 120, 130) according to claim 18, where the elongated straight passage (1210) is formed by first and second apertures spaced apart by a distance larger than a width of the apertures.

20. The light curtain device (1 10, 120, 130) according to claim 19, where at least one of the apertures is a slot with elongation direction aligned with an elongation direction of a light curtain device body (420).

21 . The light curtain device (1 10, 120, 130) according to any of claims 18-20, where the surface (1220) is arranged at an angle relative to the direction of the passage.

22. The light curtain device (1 10, 120, 130) according to claim 4, wherein the means for detecting rotation angle (£) alignment error comprises first and second photodetectors (1610, 1620) arranged with respective fields of view (L, R), where each field of view has a center direction associated with maximum gain, where the center direction angles of the first and second 31 photodetectors, measured about the axis (A) normal to the concrete surface (101 ), are different, the means for detecting rotation angle (£) alignment error further comprising a control unit (1660) configured to determine a difference in light intensity detected by the first and second photodetectors, and to detect the rotation angle (£) alignment error based on the difference in light intensity.

23. The light curtain device (1 10, 120, 130) according to claim 22, wherein the control unit (1660) configured to determine if an average light intensity of the first and second photodetectors is above a threshold (Th), and to indicate successful system alignment based on if the average light intensity of the first and second photodetectors is above the threshold (Th).

24. The light curtain device (1 10, 120, 130) according to any of claims 3-23, comprising a control unit (11 1 ) arranged to temporarily deactivate the light curtain device in response to a deactivation signal received from a remote wireless device (1800, 1900).

25. A concrete surface processing system (100), comprising a mobile perimeter access control arrangement (110, 1 1 1 , 120, 130) and a concrete surface processing machine (140), the mobile perimeter access control arrangement comprising a perimeter access control unit (1 11 ) and one or more light curtain devices (110, 120, 130) arranged to define a perimeter access controlled area (150) of the concrete surface (101 ), where the perimeter access control unit (1 11 ) is connected to the one or more light curtain devices (1 10, 120, 130), wherein at least one of the light curtain devices comprises a surface support arrangement (210) configured to support the light curtain device movably on the concrete surface (101 ), where the perimeter access control unit (1 1 1 ) is configured to trigger generation of a warning signal in response to detecting a perimeter breach by the one or more light curtain devices (1 10, 120, 130).

Description:
TITLE

A CONCRETE SURFACE PROCESSING SYSTEM WITH A PERIMETER ACCESS CONTROL SYSTEM

TECHNICAL FIELD

The present disclosure relates to machines for processing concrete and stone surfaces, such as floor grinders and troweling machines. There is disclosed a mobile light curtain system which provides perimeter access control to a work area of a concrete surface processing machine. The mobile light curtain system is particularly suitable for use with autonomous, semi-autonomous or remote controlled machines.

BACKGROUND

Concrete surfaces are commonly used for flooring in both domestic and industrial facilities. The sizes of concrete surface floors range from a few square meters for a domestic garage floor to thousands of square meters in larger industrial facilities. Concrete surfaces offer a cost efficient and durable flooring alternative and have therefore gained popularity over recent years.

Concrete surface preparation is normally performed in steps. After the concrete is poured, the surface is first troweled and then grinded flat after the surface has reached a sufficient level of maturity. A matured concrete surface can then be polished to a glossy finish if desired. A floor grinder and/or a power trowel machine can be used to process the concrete surface efficiently.

Increased procedural efficiency can be obtained from autonomous concrete surface processing machines, i.e., floor grinders and power trowels comprising control means for autonomous operation, which do not require the presence of an operator. However, such autonomous concrete surface processing machines may pose a risk to personnel and sensitive objects such as equipment and building materials on the construction site which may inadvertently enter into harmful contact with the machine as it processes the concrete surface. There is a need for safety systems which protect both objects and personnel from coming too close to the concrete surface processing machine during operation.

Obstacle detection sensors are known which detect when an autonomous robot approaches an obstacle and/or makes contact with an obstacle, see, e.g., WO20151 15954A1 . The robot can then quickly be inactivated in response to detection of the obstacle. Obstacle detection and proximity sensors can be based on, e.g., mechanical contact sensors, radar, lidar and/or ultra-sound sensors. For functional safety applications such as the above-mentioned, the sensors need to be very reliable and robust, and most likely redundant sensor systems are required. This drives overall cost and complexity of the concrete processing machine which is undesired.

Self-propelled robots which use various electrical and/or magnetic signals generated by a perimeter wire to navigate in a confined area are also known, e.g., from EP2547193B1. This type of perimeter access control system is commonly used together with robotic lawn movers but may not be suitable for concrete surface processing operations, e.g., since it may be difficult to deploy the perimeter wire.

Consequently, there is a need for a reliable, easily deployed, and cost efficient safety system for autonomous concrete surface processing operations.

SUMMARY

It is an object of the present disclosure to provide a safety system which protects personnel and sensitive equipment from coming into harmful contact with an autonomous, semi-autonomous, or remote controlled concrete surface processing machine.

This object is obtained by a concrete surface processing system comprising a mobile perimeter access control arrangement and a concrete surface processing machine arranged for autonomous or remote controlled processing of a concrete surface. The mobile perimeter access control arrangement comprises a perimeter access control unit connected to one or more light curtain devices which are arranged to define a perimeter access controlled area of the concrete surface. At least one of the light curtain devices comprises a surface support arrangement configured to support the light curtain device movably on the concrete surface, where the concrete surface processing machine comprises a machine control unit arranged to perform an emergency operation in response to receiving a wireless control signal, and where the perimeter access control unit is configured to transmit the wireless control signal in response to detecting a perimeter breach by the one or more light curtain devices. Thus, a reliable, easily deployed, and cost efficient safety system for autonomous concrete surface processing operations is provided. The mobile perimeter access control arrangement is deployed around the area to be processed, and the machine can then process the area under the assumption that no foreign objects or persons can enter without being detected by the light grid system. If the perimeter is breached, the wireless control signal is generated by the light grid system and received by the concrete surface processing machine, which can then take action, such as stopping the machine. The need for complex redundant collision avoidance systems in the concrete surface processing machine is avoided, which is an advantage.

Alternatively, the concrete surface processing system may trigger a warning signal upon breach of the perimeter.

The object, and the above-mentioned advantages and effects, are also obtained by a method for processing at least a part of a concrete surface. The method comprises deploying one or more mobile light curtain devices arranged to define a perimeter access controlled area of the concrete surface at least one of the mobile light curtain devices comprises a surface support arrangement configured to support the light curtain device movably on the concrete surface. The method comprises deploying at least one autonomous or remote controlled concrete surface processing machine within the perimeter access controlled area, processing the perimeter access controlled area by the at least one machine, and executing an emergency operation by one or more of the machines in response to detecting a perimeter breach by the one or more light curtain devices.

There is also disclosed herein a mobile light curtain device arranged to define a perimeter access controlled area of a concrete surface. The light curtain device comprises any of a focused light source for generating a beam of light, at least one photo detector for detecting a beam of light, and/or at least one mirror for reflecting an incoming beam of light in a predetermined direction, wherein the beam of light is arranged to, if obstructed, indicate a perimeter breach of the perimeter access controlled area of the concrete surface. The light curtain device also comprises a surface support arrangement configured to support the light curtain device movably on the concrete surface. The surface support arrangement allows for redeploying the light curtain device in an efficient and convenient manner. Thus, the mobile light curtain device can be used in a concrete surface processing system as described above, or in a method for processing at least a part of a concrete surface.

According to some aspects, the light curtain device is arranged to reflect and/or to receive the beam of light and comprises means for detecting rotation angle alignment error of the light curtain device about an axis normal to the concrete surface with respect to the beam of light. This means that deployment of the mobile light curtain devices disclosed herein is simplified, since the operator is supported during the deployment by the means for detecting rotation angle alignment error. The performance of the mobile perimeter access control arrangement is also improved since a correct alignment of light grid devices improves the light intensity of the received light beam or beams at the receiver, which means that it becomes easier to determine when the light beam is not obstructed, i.e., that the perimeter is not being breached.

The surface support arrangement optionally comprises one or more foldable legs arranged around a central supporting foot. The legs provide additional stability to the surface support arrangement. The legs can also be folded into a folded position. The light curtain device can therefore be placed snug into a corner or against a wall, since the legs, when folded, do not protrude from the surface support arrangement.

The surface support arrangement may also comprise a supporting plate configured to fit snugly in a corner. This allows the concrete surface processing system to process surfaces close to corners, which is an advantage.

According to aspects, the surface support arrangement is configured to receive and to hold one or more weights for weighting down the light curtain device against the concrete surface. The weights provide an extra degree of stability to the light curtain device, which means that it is not so easily knocked over. It is also able to handle strong vibration and the like without shifting from the deployment position.

According to aspects, the surface support arrangement comprises one or more integrated wheels arranged to support the light curtain device on the concrete surface in a transport mode of the light curtain device. The wheels simplify transportation of the light grid device. The light curtain device may also comprise a handle arranged to allow an operator to lift the light curtain device from the concrete surface and carry the light curtain device. The handle can also be used when transporting the light grid device by the integrated wheels.

The light curtain device optionally comprises an integrated spirit level configured to indicate a pose of the light curtain device relative to a horizontal plane. This spirit level may either be an analog spirit level or an equivalent digital implementation of a spirit level, such as one based on a gyro or inertial measurement unit (IMU). This spirit level allows for an initial course alignment of the mobile light curtain device with respect to a ground plane. Thus, if all mobile light grid devices in a system are aligned in this manner, a significant portion of angular misalignments, in particular regarding tilt, can be mitigated in an efficient manner.

According to some other aspects, the light curtain device also comprises a status indicator light arranged visible from a location distant from the light curtain device. This status indicator light make is easier for an operator or some other person to determine a current status of the mobile light grid system, such as if the system is fully operational, if some error event has occurred, if the perimeter has been breached, and so on. The status indicator light can, for instance, be arranged integrated with a handle on the light curtain device.

To simplify correction of light curtain device tilt angle, a light curtain device body section may optionally be attached to the surface support arrangement by a ball joint. This ball joint is preferably but not necessarily a lockable ball joint. This lockable ball joint can also be arranged to be released by a pedal mechanism biased towards a locked position of the ball joint, wherein the ball joint is arranged to be released from the locked position by depressing the pedal mechanism.

The light curtain device may furthermore comprise an extendable distance measuring member configured to indicate a maximum separation distance with respect to a distant light curtain device. This distance measuring member may, e.g., resemble an extendable tape measure or extendable string which is configured to indicate a suitable distance between light curtain devices.

According to other aspects, the surface support arrangement comprises at least one levelling mount configured to adjust an angle of the surface support arrangement relative to a supporting concrete surface. This leveling mount cooperates with the ball joint to provide an even deployment of the surface support arrangement. The levelling mount can of course also be used without the ball joint. Advantageously, the levelling mount may be used to compensate for unevenness in the concrete surface, such as small bumps, holes, and the like.

The means for detecting rotation angle alignment error optionally comprises an elongated straight passage terminated by a surface, configured to allow a light beam from a distant guiding light source to traverse the passage and illuminate the surface from a predetermined range of angles. The passage has a width measured perpendicular to the passage direction of the beam of light smaller than an extension length of the passage. This arrangement allows an operator to quickly determine if the light grid device is aligned with respect to a distant light grid device. If the light beam from the guiding light source, which may, e.g., be a laser or the like, hits the surface, then the light beam has traversed the passage and therefore originates from a location within the allowable range of angles.

The elongated straight passage can, for instance, be formed by first and second apertures spaced apart by a distance larger than a width of the apertures. At least one of the apertures can be implemented as a slot with elongation direction aligned with an elongation direction of a light curtain device body. This way a tilt angle error does not affect the ability of the beam of light to traverse the passage, and the alignment can be focused on setting a correct rotation of the mobile light grid device about the axis normal to the concrete surface.

The surface is optionally arranged at an angle relative to the direction of the passage. This angle means that an operator can view the surface conveniently.

According to other aspects, the means for detecting rotation angle alignment error comprises first and second photodetectors arranged with respective fields of view, where each field of view has a center direction associated with maximum gain, where the center direction angles of the first and second photodetectors, measured about the axis normal to the concrete surface, are different. The means for detecting rotation angle alignment error further comprises a control unit configured to determine a difference in light intensity detected by the first and second photodetectors, and to detect the rotation angle alignment error based on the difference in light intensity. This arrangement allows for alignment of rotation angles without the use of a guiding light source, such as a laser. Instead, the normal light grid light source is used for rotation angle alignment.

According to further aspects, the control unit is configured to determine if an average light intensity of the first and second photodetectors is above a threshold, and to indicate successful system alignment based on if the average light intensity of the first and second photodetectors is above the threshold. This allows the system to determine if a sufficient light intensity has been achieved. For instance, if two light grid devices are placed too far apart, then this mechanism will indicate that the light intensity is too weak to permit stable operation of the system. An error signal can be generated in case the deployment does not meet requirements in terms of light intensity.

The light curtain device optionally comprises a control unit arranged to temporarily deactivate the light curtain device in response to a deactivation signal received from a remote wireless device. This deactivation signal can be used by an operator wishing to enter the area to, e.g., inspect the result of the concrete processing.

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. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described in more detail with reference to the appended drawings, where

Figure 1 illustrates a concrete surface processing operation;

Figure 2 illustrates light curtain device misalignment;

Figures 3-5 show example mobile light curtain devices; Figures 6-9 illustrate details of example surface support arrangements;

Figures 10-1 1 illustrate example surface support arrangement geometries;

Figure 12 illustrates a principle of light curtain device alignment;

Figure 13 shows a light curtain emitter device;

Figures 14-15 show example light curtain device alignment arrangements;

Figures 16-17 illustrate another principle of light curtain device alignment;

Figures 18-19 show example light curtain control devices;

Figure 20 is a flow chart illustrating methods;

Figure 21 schematically illustrates a control unit; and

Figure 22 shows a computer program product;

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain aspects 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 and aspects 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.

It is to be understood that the present invention is not limited to the embodiments described herein and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Figure 1 shows a concrete surface processing system 100. The system comprises a concrete surface processing machine 140 arranged for autonomous, semi-autonomous, or remote controlled processing of a concrete surface. The concrete surface processing machine 140 may, e.g., be a floor grinder or a power troweling machine, or some other form of concrete surface processing machine. These machines may be arranged for autonomous operation, i.e., for operation without direct control of an operator via manual control input device. The operation may be fully autonomous or semi-autonomous, i.e., requiring some instructions from an operator but no direct control of the machine. This input may be provided from a remote control device 1800 of the type illustrated in Figure 18, or from some other type of wireless device, such as a smart phone 1900 (shown in Figure 19) or similar type of wireless device arranged to communicate with the concrete surface processing machine 140. The concrete surface processing machine 140 may also be remote controlled by an operator from a distance, e.g., by the remote control device 1800.

The machine 140 processes the concrete surface by following some path P over the surface, where the path is confined to lie within some area 150 of the concrete surface. Machines of the above-mentioned types and for this purpose are known and will therefore not be discussed in more detail herein.

Autonomous, semi-autonomous, and remote control operation of heavy machinery such as floor grinders and power trowels may be associated with some risk. Construction site workers may inadvertently come to close to the machine and thereby risk injury if the machine enters into harmful contact, i.e., collides with, the worker. Other stationary and mobile objects, such as other construction tools and sensitive building materials may also be mistakenly placed in the path of the autonomous machine, which may result in a collision with the machine and result in damage both to the machine and to the object.

Robotic machines equipped with collision avoidance systems comprising advanced proximity sensors and control units which mitigate these risks are known. However, such advanced sensor systems are complex and require extensive testing and validation, which is undesired.

The concrete surface processing system 100 shown in Figure 1 comprises a mobile perimeter access control arrangement. This mobile perimeter access control arrangement comprises a perimeter access control unit 1 1 1 connected to one or more mobile light curtain devices 1 10, 120, 130 arranged to define a perimeter access controlled area 150 of the concrete surface by the transmission of a light beam 160. The perimeter access control unit 1 1 1 may be arranged integrated with one or more of the devices 1 10, 120, 130, or arranged external to the devices 1 10, 120, 130. The perimeter access control unit may also be distributed over the different devices, and/or at least party executed on a remote device 170 connected to the concrete surface processing system 100 via wireless or wireline link 180. A general example of a control unit will be discussed in more detail below in connection to Figure 21 .

A light curtain is an optical safety device comprising one or more light sources (emitters) which generate light beams that are detected by photo detectors (receivers). An object traversing past the light curtain can be detected since one or more of the light beams is blocked. When at least one of the photo detectors loose the incoming light beam, it generates a signal to the control unit 11 1. Light curtain systems are known in general. They are commonly used for perimeter access control in manufacturing facilities where they are fixedly deployed to provide a safety perimeter around manufacturing robots and the like.

Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. A photo detector has a p-n junction that converts light photons into current. The absorbed photons make electron-hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors.

In the example of Figure 1 , the emitters 1 10 generate light beams 160 which traverse via mirrors 130 to photo detectors 120, where it is appreciated that the mirrors are optional since a plurality of emitters and receivers can be used to define the same type of area. The light curtain devices 1 10, 120, 130 define a perimeter access controlled area 150 of the concrete surface. A person entering into this area 150 will obstruct one or more light beams and will therefore be detected by the system. The machine 140 comprises a machine control unit 101 , which will be discussed in more detail below in connection to Figure 21 . The machine control unit 101 is arranged to perform an emergency operation, such as coming to a full stop or slowing down significantly in response to receiving a wireless control signal 1 12. The perimeter access control unit 1 11 is configured to transmit the wireless control signal 1 12 in response to detecting a perimeter breach by the one or more light curtain devices 1 10, 120, 130. In other words, if the light beam is obstructed, one or more photo detectors on the receivers 120 will react to the loss of incoming light and notify the perimeter access control unit 1 1 1. This will trigger an action by the perimeter access control unit 11 1 , which action comprises interacting with the control unit 101 on the machine 140.

The system 100 in Figure 1 does not require complex sensor systems arranged on the concrete surface processing machine 140, which is an advantage. The complexity of the concrete surface processing safety system is instead concentrated to the mobile perimeter access control arrangement, i.e., the one or more light curtain devices 1 10, 120, 130 and the control unit 11 1. This voids the need for, e.g., redundant expensive sensor systems on the machine itself, which is an advantage. Also, several concrete surface processing machines 140 can be deployed inside the same perimeter to collectively process the area 150. This way the safety equipment can be reused for more than one machine 140, which is an advantage.

Alternatively, the system may just trigger a warning signal, such as an alarm signal comprising sound and/or lights, upon perimeter breach. This, there is also disclosed herein a concrete surface processing system comprising a mobile perimeter access control arrangement 1 10, 11 1 , 120, 130 and a concrete surface processing machine 140. The mobile perimeter access control arrangement comprises a perimeter access control unit 1 1 1 connected to one or more mobile light curtain devices 1 10, 120, 130 arranged to define a perimeter access controlled area 150 of the concrete surface 101 , wherein at least one of the light curtain devices comprises a surface support arrangement 210 configured to support the light curtain device movably on the concrete surface 101 , and where the perimeter access control unit 1 11 is configured to trigger generation of a warning signal in response to detecting a perimeter breach by the one or more light curtain devices 1 10, 120, 130.

It is noted that the perimeter also acts to ensure that the machine 140 does not stray away from the area 150. If something goes wrong, perhaps due to an erroneous configuration in a control unit 101 for autonomous operation, or a mistake in the operator input to a remote control device, the machine 140 itself will breach the perimeter and thus trigger the response by the control unit 1 1 1.

Advantageously, at least one of the light curtain devices comprises a surface support arrangement which will be discussed in more detail below. The surface support arrangement is configured to support the light curtain device movably on the concrete surface 150. This means that the perimeter access control arrangement is mobile and can easily be re-deployed once the concrete processing operation has finished. The system 100 is easily transported since the light curtain devices are movable. Once the concrete surface processing operation finishes a new perimeter can be set up by simply relocating the devices 1 10, 120, 130 to some other area on the construction site or to some other construction site. The components of the system 100 are compact which allows for efficient storage and transportation. Indeed, the machine 140 can be fitted with brackets for holding a number of light curtain devices. This way the machine can be transported together with the necessary light curtain devices for setting up a perimeter.

The disclosed safety system is easy to set up, mechanically robust, and does not require complex sensor systems on the concrete processing machine, which is an advantage. The safety system is also relatively low cost.

A potential drawback with a mobile perimeter access control arrangement like the system 100 in Figure 1 is the time it takes to set up the system following a re-location. The different devices 1 10, 120, 130 must be carefully positioned and aligned with each other to connect emitters to receivers, i.e., such that the emitted light beams 160 illuminate the respective receivers. Misalignment is likely to result in reduced performance and potential system failure.

Figure 2 illustrates a few different types of light curtain device misalignments which may occur. Angle oc is a tilt of the light curtain device 120 with respect to an axis A normal to the concrete surface 101 away from the emitter 1 10. The optimal angle oc is about zero degrees in the example. A deviation in angle oc of about 0.4 degrees may be acceptable in most light curtain systems. Thus, alignment to within +/- 0.4 degrees is desired and may even be required.

Angle £ is a rotation of the light curtain device with respect to the axis A. A pose where (3=0 is desired. A deviation in angle £ of about 0.55 degrees may be acceptable in most light curtain systems. Thus, alignment to within +/- 0.55 degrees is desired and may even be required.

Angle y is a tilt of the light curtain device with respect to the axis A in a plane perpendicular to a direction of the emitter. A pose where y=0 is desired. A deviation in angle y of about 8.8 degrees may be acceptable in most light curtain systems. Thus, alignment to within +/- 8.8 degrees is desired and may even be required.

In the examples of Figure 2, the receiver sensors 220 are arranged in recesses which prevent the beam of light from reaching the sensors if the misalignment is too large. Even if no such recesses exist, there is normally a lens arranged in front of the receiving sensors, which focuses received energy from a certain direction. This lens is associated with a pointing direction or boresight direction where the gain is the largest. If this pointing direction is not directed towards the light source on the emitter, then the intensity of the received light decreases, which results in a reduced performance or even system failure.

Consequently, all of these alignment errors affect the performance of the light curtain system in a negative manner since the light intensity at the detector is reduced by the misalignment. However, most light curtain devices are more sensitive to errors in angle oc and £ compared to angle y. This can intuitively be explained by the amplification by distance affecting the angles oc and £ and not the angle y.

Figure 20 is a flow chart which illustrates a method for processing at least a part of a concrete surface 101 by a concrete processing system such as that discussed above in connection to Figure 1. The method comprises deploying S1 one or more mobile light curtain devices 110, 120, 130 arranged to define a perimeter access controlled area 150 of the concrete surface 101 , wherein at least one of the mobile light curtain devices comprises a surface support arrangement 210 configured to support the light curtain device movably on the concrete surface 101 , i.e., such that it can be re-located by an operator in a convenient manner and without requiring any complex tools or the like. The method also comprises deploying S2 one or more autonomous or remote controlled concrete surface processing machines 140 within the perimeter access controlled area 150, processing S3 the perimeter access controlled area 150 by the one or more machines 140 and executing S4 an emergency operation by at least one of the machines 140 in response to detecting a perimeter breach by the one or more light curtain devices 1 10, 120, 130. The emergency operation may, e.g., comprise halting one or more of the deployed machines, slowing down a forward motion by the machines, or triggering an alarm signal.

Figures 3-5 illustrate examples of mobile light curtain devices 1 10, 120, 130 which can be used in combination to define a perimeter access controlled area 150 of a concrete surface 101 , as exemplified in Figure 1 . Figure 3 illustrates an example emitter 110 which is arranged to generate a beam of light 160 focused in a given direction. This beam of light is then detected by a receiver 120 illustrated in Figure 4. In case a change of direction of the beam of light 160 is desired, a mirror device 130 illustrated in Figure 5 can be used to redirect the beam of light. The example system 100 discussed above in connection to Figure 1 comprised two emitters 1 10 and two receivers 120, where each beam of light was diverted by a respective mirror device 130. The mobile light curtain devices discussed herein are not necessarily identical in features to the mobile light curtain devices of Figures 3-5, rather, these devices are to be considered as example embodiments of the herein disclosed general mobile light curtain device.

To summarize, there is disclosed herein a mobile light curtain device 1 10, 120, 130 arranged to define a perimeter access controlled area 150 of a concrete surface 101 . The light curtain device comprises any of a focused light source 310 for generating a beam of light 160, a photo detector 410 for detecting a beam of light 160, and/or a mirror 510 for reflecting an incoming beam of light 160 in a predetermined direction, wherein the beam of light 160, if obstructed, indicates a perimeter breach of the perimeter access controlled area 150 of the concrete surface 101. The light curtain device also comprises a surface support arrangement 210 configured to support the light curtain device movably on the concrete surface 101 .

Thus, the light curtain devices discussed herein are mobile in the sense that they comprise surface support arrangements 210 which allow the mobile light curtain devices to be robustly supported on the concrete surface 101 , and at the same time to be easily re-locatable in a convenient manner simply by an operator lifting the mobile light curtain off the surface and re-locating the mobile light curtain to a new location, which new location may be an overlapping area of concrete surface, or an area on an entirely different construction site. The mobile light curtain devices described herein are relatively light weight and are easily configurable to define a safety perimeter.

The surface support arrangements 210 optionally comprise one or more integrated wheels 320 arranged to support the light curtain device on the concrete surface 101 in a transport mode of the light curtain device. For instance, as in the examples shown in Figures 3 and 5, the wheels 320 can be arranged distanced from the surface when the mobile light device is in the operating position, i.e., when it is supported fully by the surface support arrangement 210 on the concrete surface. The wheels make contact with the concrete surface if the mobile light curtain device is tilted in direction of the wheels 320. An operator can then easily move the mobile light curtain device 110, 130 around on the concrete surface 101. Alternatively, the wheels 320 may form part of the support also in an upright position (not tilted). An example of this type of arrangement is shown in Figure 4 and Figure 6, where two wheels are paired to make up one out of three support points of the surface support arrangement 210.

The surface support arrangement 210 may furthermore comprise at least one levelling mount 340 configured to adjust an angle of the surface support arrangement 210 relative to a supporting concrete surface. This levelling mount allows for an alignment of a central axis of the body 420 relative to the concrete surface. It is often desirable that this central axis is parallel to a normal vector of the concrete surface. The adjustable mounts can also be used to compensate for unevenness in the concrete surface 101 , i.e., smaller holes and bumps which may be present prior to the concrete processing operation.

The light curtain device may comprise a handle 330 arranged to allow an operator to lift the light curtain device from the concrete surface 101 and carry the light curtain device. The handle can also be used when tilting the mobile light curtain device, such as when the wheels are to be used for re-locating the light curtain device in tilted position. Notably, the handle extends in a direction perpendicular to the direction of the wheels, such that an operator may conveniently push or pull the mobile light curtain device on the concrete surface when the mobile light curtain is in the tilted position and supported by the wheels 320 on the concrete surface.

The mobile light curtain devices 1 10, 120, 130 disclosed herein may furthermore comprise a status indicator light 440 arranged visible from a location distant from the light curtain device. An example of this indicator light 440 is shown in Figure 4, where it has been arranged integrated with the handle 330 on the light curtain device. This status indicator light is arranged close to the top of the device, i.e., at an end opposite from the side of the surface support arrangement 210. It is arranged such that it can be seen from all angles, or at least from most viewing angles. Thus, an operator located in a position distanced from the mobile light curtain device can visually observe the status indicator light and thus obtain information about the status of the mobile light curtain device. For instance, a solid green light may indicate that the safety system is active and that no errors have occurred. A flashing red light may indicate that the perimeter has been breached. A solid red light may indicate that some error has occurred. The handle portion 330 may also serve as the status indicator light, by arranging a transparent handle with light emitting diodes inside configured to generate light in different colors. This the entire handle 330 lights up and can be easily seen even from a distant location.

The mobile light curtain devices 1 10, 120, 130 comprise body sections 420 attached to the respective surface support arrangements 210 Optionally, these body sections are arranged movable relative to the surface support arrangements in height H and/or in rotation angle R. The height adjustment may be implemented by a telescopic arrangement or guide rail, while the rotation can be achieved by a rotatable attachment between body 420 and surface support 210.

The light curtain device 1 10, 120, 130 may also comprise an extendable distance measuring member configured to indicate a maximum separation distance to a distant light curtain device. Thus, an operator can extend an integrated tape measure or the like to verify that the light curtain devices are not positioned too far apart.

Figure 6 illustrates an optional attachment mechanism for attaching the body 420 to the surface support 210. In this example, the light curtain device body section 420 is attached to the surface support arrangement 210 by a ball joint 430. This ball joint allows for adjusting the tilt pose of the body 420 relative to the concrete surface, and also rotation R about a central axis of the body. According to some aspects, the ball joint 430 is a lockable ball joint. Lockable ball joints are generally known and will therefore not be discussed in more detail herein. Advantageously, the lockable ball joint can be arranged to be released by a pedal mechanism 610 biased towards a locked position of the ball joint, wherein the ball joint is arranged to be released from the locked position by depressing the pedal mechanism. This pedal mechanism allows for an operator to release the lockable ball joint in a convenient manner.

Figure 7 illustrates another type of surface support arrangement 210 which comprises one or more foldable legs 710 arranged around a central supporting foot 720. The legs can be folded up or down depending on where the mobile light curtain device is to be placed. For instance, if the mobile light curtain device is deployed against a wall or in a corner, than only one or two legs may be required, with the legs facing the wall being folded up and the legs facing away from the wall being folded down to support the light curtain device.

Generally, it is an advantage if the surface support arrangement 210 is shaped to fit into a corner. The surface support arrangement 210 shown in Figure 8 comprises a supporting plate 810 configured to fit snugly in a corner 1000. This means that the concrete surface processing machine 140 can process a large part of the concrete area 101 without coming into contact with the mobile light curtain device.

According to some aspects, exemplified in Figure 9, the surface support arrangement 210 is configured to receive and to hold one or more weights 910 for weighting down the light curtain device against the concrete surface 101. This can, e.g., be achieved by adding a protruding pin or tap from the surface support arrangement adapted to hold weights with holes matched to the dimension of the protrusion.

It is an advantage that the light curtain devices discussed herein can be deployed to fit snugly into corners. Figures 10 and 11 illustrate a concrete processing operation involving a corner 1000. Figure 10 shows a light curtain device with a surface support arrangement 210 comprising two arms extending along a baseline and a third arm extending perpendicular from a center of this baseline to form a triangle as illustrated in Figure 10. This shape is configured to fit snugly into a corner. An L-shaped surface support arrangement such as that illustrated in Figure 8 also has this property. Normally, a section 1020 close to the wall is left unprocessed when processing concrete surfaces. This section is then processed using a different type of tool.

Figure 1 1 shows another example of concrete surface processing in a corner 1000. Here, two light curtain devices have been deployed in the corner.

As discussed above in connection to Figure 2, the mobile light curtain system may suffer performance degradation or even system failure if the receiver 120 and/or mirror device 130 is not properly aligned with the direction of the incoming beam of light 160 from the emitter 1 10. The tilt angles oc and y illustrated in Figure 2 can normally be sufficiently accurately configured using, e.g., an analog spirit level or a digital spirit level based on, e.g., an inertial measurement unit (IMU). However the rotation angle £ is more difficult.

To provide accurate alignment between emitter and receiver, in particular with respect to the rotation angle £, the light curtain devices 120, 130 arranged to reflect and/or to receive the beam of light 160 optionally comprise means for detecting rotation angle £ alignment error of the light curtain device about an axis A normal to the concrete surface 101 with respect to the beam of light 160.

Figures 12-15 illustrate a first example mechanism for aligning the mobile light curtain device with respect to the beam of light. Figures 16-17 illustrate a second example mechanism for aligning the mobile light curtain device with respect to the beam of light. To allow course adjustment of light curtain device tilt with respect to the concrete surface, the light curtain devices 1 10, 120, 130 optionally comprise an integrated spirit level 1320, 1410, 1510 configured to indicate a pose of the light curtain device relative to a horizontal plane. This spirit level can be an analog spirit level, or a digital spirit level connected to a remote control 1800 or a wireless device 1900, such as those illustrated in Figures 18 and 19.

The means for detecting rotation angle £ alignment error may comprise an elongated straight passage 1210 terminated by a surface 1220, as schematically illustrated in Figure 12. The passage is configured to allow a light beam 1230 from a distant guiding light source to traverse the passage and illuminate the surface, as shown in the upper part (I) of Figure 12. If the guiding beam of light arrives from an angle larger than the allowable angular range, the guiding beam of light will be blocked from passage and will not illuminate the surface, as shown in the bottom part (II) of Figure 12. The passage has a width measured perpendicular to the passage direction D of the beam of light smaller than an extension length L of the passage. This means that the beam of light from the guiding light source may only traverse the passage 1210 and illuminate the surface 1220, where it can be observed by an operator, if it arrives from one out of a pre-determined range of angles relative to a boresight direction of the light curtain device. The range of angles depends on the width of the passage in relation to its length, a suitable range of angles may be on the order of a degree, and preferably less than one degree. A preferred angular range may be from -0.55 degrees to 0.55 degrees. A wide and short passage will allow for a larger angular range, while a narrow and long passage will place more strict requirements on angular alignment in order for the beam of light to traverse the passage and illuminate the surface.

The elongated straight passage 1210 can, for instance, be formed by first and second apertures spaced apart by a distance larger than a width of the apertures, as shown in Figure 12. More than two apertures can of course also be used. Alternatively, the passage can be formed by a tubular structure, such as a rectangular cross-section pipe with a length configured in dependence of the opening width of the pipe to obtain the desired angular range. A circular cross-section pipe can also be used for the same effect. The passage may also comprise one or more lenses arranged to focus incoming light from a predetermined range of directions, i.e., lenses having a lens pattern configured in dependence of the desired angular range.

Figure 13 shows a light curtain device 1 10 comprising a guiding light source 1310. This guiding light source may, e.g., be a laser emitter configured to emit a guiding beam of light in the same direction as the beam of light 160 from the emitting light curtain device 1 10. The laser may be a point laser or a line laser. A line laser may be advantageously used together with the slotted apertures illustrated in Figure 12. To align the emitter 1 10 with a receiver 120 and/or with a mirror 130, the emitter is first deployed in approximately the right location and coarsely directed towards the location of the mirror device or the receiver. The guiding light source 1310 is then activated, whereupon the mirror device 130 and/or the receiver 120 can be aligned with respect to the emitter. The system can then be turned on, and functionality can be verified. For instance, if status indicator lights 440 are arranged integrated with the receiver 120, or with some other light curtain device, then the operator can make sure that the system is fully functional by observing the status indicator lights.

It is appreciated that the guiding light source 1310 can be fitted to any of the emitter light curtain device 1 10, the receiver light curtain device 120, or to the mirror light curtain device 130.

Figure 14 illustrates an example receiver light curtain device 120 where the apertures are formed as slots with elongation direction aligned with an elongation direction of the light curtain device, i.e., parallel to the axis A.

Figure 15 shows an example mirror light curtain device 130. Here, two passages have been formed in order to be able to align the mirror device with two adjacent light curtain devices.

The surface 1220 can be arranged at an angle w relative to the direction of the passage, as shown in Figures 14 and 15, and in particular in the insert of Figure 14. This angle w allows an operator to observe if the beam of light illuminates the surface or not simply by looking down into the light curtain device from direction of the handle 330, as shown in the insert of Figure 14. The angle of the surface 1220 may suitably be on the order of 45 degrees or so.

Figure 16-17 illustrate an alternative means for detecting rotation angle £ alignment error. Here, the means for detecting rotation angle £ alignment error comprises first and second photodetectors 1610, 1620 arranged with respective fields of view L, R, where each field of view has a center direction associated with maximum gain, where the center direction angles of the first and second photodetectors, measured about the axis A normal to the concrete surface 101 , are different. The means for detecting rotation angle £ alignment error further comprises a control unit configured to determine a difference in light intensity detected by the first and second photodetectors, and to detect the rotation angle £ alignment error based on the difference in light intensity.

In Figure 16, two photodetectors 1610, 1620 have been arranged to either side of a central main photo detector 1630. It is desired to maximize the light intensity at the central photo detector 1630. To maximize this light intensity, the light intensities of the left and right detector should be equal (as illustrated in the insert diagram 1670), otherwise there is a bias in angle towards the stronger of the two. Thus, the control unit 1660 can compare the light intensities and indicate to an operator which way to turn the light curtain device to align with the distant emitter 1640 in order to receive the beam of light 1650 with maximum light intensity.

The control unit 1660 can also be configured to determine if an average light intensity of the first and second photodetectors is above a threshold Th, and to indicate successful system alignment based on if the average light intensity of the first and second photodetectors is above the threshold Th.

It is appreciated that the left and right photo detectors 1610, 1620 can be integrated into a single unit as shown in Figure 17. A lens with two lobes can then be fitted, and the photo detectors can be wired to output a difference of the two intensities, similar to a motion detector based on passive infra-red sensors. The insert diagram 1680 illustrates the output from this alignment sensor. If the light curtain device is not correctly aligned to the emitter 1640 which emits the beam of light 1650, then there will be an output from the alignment sensor 1610, 1620. The sign of this output indicates which way to rotate the light curtain device in order to improve the alignment with respect to the distant light source 1640. Figures 18 and 19 illustrate examples devices 1800, 1900 for remotely controlling a concrete surface processing machine and/or for monitoring the mobile perimeter access control arrangement. The devices 1800, 1900 may, e.g., connect wirelessly to the control unit 1 1 1 and receive status reports indicative of the status of the mobile perimeter access control arrangement, such as if the perimeter is or has been breached, whether the system is up and running, or if there is some issue with the hardware or set-up. The 1800, 1900 may also be used to temporarily deactivate the mobile perimeter access control arrangement to allow an operator to cross the perimeter. Thus, an operator can cross the perimeter to verify a grinding result without the system triggering the warning signal. This temporary deactivation of the safety system may be preceded by an authorization procedure or a double-check to verify that the deactivation is truly intended and not mistakenly triggered. The deactivation procedure may be configured to require an identification of the operator, such that only a select group of operators are authorized to deactivate the light grid temporarily. The light grid may automatically be reactivated after a pre-determined or manually configurable time period sufficient for allowing the operator to cross the perimeter, e.g., on the order of a few seconds.

Thus, the light curtain systems discussed herein may comprise a control unit 11 1 arranged to temporarily deactivate the light curtain device in response to a deactivation signal received from a remote wireless device 1800, 1900.

It is appreciated that many if not most of the different features discussed herein are independent of each other and can be implemented as stand-alone features on a light grid device. For instance, the features relating to alignment can just as well be applied to a fixed light grid system, i.e., one mounted fixedly by brackets bolted to walls or the like. The features related to mobility does not require the alignment mechanisms to operate, known alignment methods can also be used, albeit with reduced efficiency.

Thus, there is disclosed herein a mobile light curtain device 110, 120, 130 arranged to define a perimeter access controlled area 150 of a concrete surface 101 , the light curtain device comprising any of a focused light source 310 for generating a beam of light 160, at least one photo detector 410 for detecting a beam of light 160, and/or at least one mirror 510 for reflecting an incoming beam of light 160 in a predetermined direction, wherein the beam of light 160 is arranged to, if obstructed, indicate a perimeter breach of the perimeter access controlled area 150 of the concrete surface 101 , wherein the light curtain device comprises means for detecting rotation angle £ alignment error of the light curtain device about an axis A normal to the concrete surface 101 with respect to the beam of light 160.

Figure 21 schematically illustrates, in terms of a number of functional units, the general components of a control unit 101 , 1 1 1 , 2100. Processing circuitry 2110 is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium 2130. The processing circuitry 21 10 may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

Particularly, the processing circuitry 21 10 is configured to cause the device 110, 120, 130, 140 to perform a set of operations, or steps, such as the methods discussed in connection to Figure 20 and the discussions above. For example, the storage medium 2130 may store the set of operations, and the processing circuitry 2110 may be configured to retrieve the set of operations from the storage medium 2130 to cause the device to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 2110 is thereby arranged to execute methods as herein disclosed.

The storage medium 2130 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The control unit may further comprise an interface 2120 for communications with at least one external device. As such the interface 2120 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.

The processing circuitry 21 10 controls the general operation of the control unit, e.g., by sending data and control signals to the interface 2120 and the storage medium 2130, by receiving data and reports from the interface 2120, and by retrieving data and instructions from the storage medium 2130. Figure 22 illustrates a computer readable medium 2210 carrying a computer program comprising program code means 2220 for performing the methods illustrated in Figure 20 and discussed herein, when said program product is run on a computer. The computer readable medium and the code means may together form a computer program product 2200.