EP2789766A1

EP2789766A1 - Floor treatment device and a safety method for a floor treatment device.

Info

Publication number: EP2789766A1
Application number: EP13163610.2A
Authority: EP
Inventors: Per Niva; Linus Holmeros; Erland Lewin; Jan Lewerentz
Original assignee: Swepac AB
Current assignee: Swepac AB
Priority date: 2013-04-12
Filing date: 2013-04-12
Publication date: 2014-10-15

Abstract

The present invention relates to a floor treatment device (1) drivable by an engine (40), said floor treatment device (1) comprising an accelerometer unit (11) mounted on a chassis (6) of said floor treatment device (1) and adapted to monitor an rotational movement of said chassis (6). The floor treatment device (1) further comprises a controller (12) connected to said floor treatment device (1) and adapted to stop motion of said floor treatment device (1) when said rotational movement satisfies a safety criteria. The present invention further relates to a safety method for a floor treatment device (1).

Description

FIELD OF THE INVENTION

The present invention relates to a floor treatment device and a safety method for a floor treatment device, in particular a trowel and a safety method for a trowel.

BACKGROUND OF THE INVENTION

Floor treatment devices comprising rotating floor treatment members are used within a number of fields such as finishing, grinding, polishing and cleaning of floors. These machines usually comprise an engine of a suitable type depending on the application and a rotor driven by the engine.
Commonly, such floor treatment devices are provided with a safety clutch which in an emergency, i.e. if the operator loses control of the floor treatment device, automatically stops the engine. If such floor treatment device goes out of control of the operator, unintentional contact, or impact, between the floor treatment device and surrounding walls or side surfaces may occur, resulting in damage to the floor treatment device and/or damages to the walls or side surfaces.
In particular, this is a concern when using devices known as trowels, or power trowels, which are used to smoothen or even concrete surfaces or surfaces of setting concrete. Power trowels are normally heavy duty machines comprising powerful engines and are hence able to cause significant damage to walls or side surfaces in the case of impact.
An example of a known safety clutch is a lever which is activated by the centrifugal force when the rotary trowel goes out of control in an emergency situation. Such a floor treatment device comprising a safety clutch is known from US4232980 A . US4232980 A discloses a rotary power trowel having a safety clutch, a gyroscopic stabilizing ring, blade pitch control, and an adjustable handle. The safety clutch employs a belt tension adjustment to act as a brake on the drive belt when activated either manually or, in an emergency, automatically by a lever on a handle near the operator. When the rotary trowel goes out of control in an emergency, centrifugal force activates the lever and disengages the driving force and acts to brake the belt in less than one turn of the handle.
Another example of a safety arrangement for a floor treatment device is known from EP1529898 B1 which discloses a control module for a walk behind trowel configured to detect and to prevent an uncontrolled or undesirable motion of the trowel. The trowel includes an engine configured to drive rotation of a rotor. The control module includes a gyroscope and a controller. The gyroscope is configured to provide an electrical signal representative of an angular rate of motion of a reference structure on the walk behind trowel. The controller is configured to receive the electrical signal from the gyroscope and to determine when a change in the angular rate of motion of the trowel exceeds a threshold value, and in response, to prevent the engine from driving the rotor to rotate.
Safety arrangements for floor treatment devices using gyroscopes have been proven to work well, however, the inventors of the present invention have identified a need for an improved emergency stop device for a floor treatment device, which is straightforward to manufacture and more cost-effective.
Thus, an object of the present invention is to provide an improved emergency stop device for a floor treatment device which is cost-effective and straightforward to manufacture.
A further object of the present invention is to provide an alternative way of providing an emergency stop for a floor treatment device.
Still another object of the present invention is to provide an improved emergency stop device which is reliable and safe.
Yet another object of the present invention is to provide a safety method for a floor treatment device which is reliable and safe.

SUMMARY OF THE INVENTION

The above-mentioned objects are achieved by the present invention according to the independent claim.
Preferred embodiments are set forth in the dependent claims.
According to a first aspect of the invention, the floor treatment device drivable by an engine, comprises an accelerometer unit mounted on a chassis of said floor treatment device and adapted to monitor an rotational movement of said chassis. The floor treatment device further comprises a controller connected to said floor treatment device and adapted to stop motion of said floor treatment device when said rotational movement satisfies a safety criteria.
In other words, the floor treatment device comprises a chassis to which the engine is mounted. The engine may be an electrical or combustion engine. The floor treatment further comprises an accelerometer unit mounted on the chassis and is adapted to monitor the rotational movement of said chassis, i.e. the rotational movement of the chassis relative the rotor with its thereto connected blades. The floor treatment device further comprises a controller connected to said floor treatment device, i.e. the controller is connected to the accelerometer unit and is adapted to receive a monitor signal representing the rotational movement from the accelerometer unit. When said monitor signal satisfies a safety criteria, i.e. a predetermined or calculated criteria, the controller is further adapted to stop said floor treatment device.
According to a second aspect of the invention, there is provided a safety method for a floor treatment device. The method comprises:

providing an accelerometer unit, mounted on a chassis of said floor treatment device; (a1)
monitoring an rotational movement of said chassis of said floor treatment device using said accelerometer unit; (a2)
comparing said monitored rotational movement with a threshold value of said rotational movement; (a3)
generating a stop control signal S1 if said threshold value has been reached or exceeded, said stop control signal S1 being configured to stop or disconnect said connectable engine from driving said floor treatment device. (a4)

In other words, according to a second aspect of the invention, there is provided a safety method for a floor treatment device. The method comprises:

providing an accelerometer unit, mounted on a chassis of said floor treatment device; (a1)
monitoring an rotational movement of said chassis of said floor treatment device using said accelerometer unit; (a2)
stopping the motion of said floor treatment device when said rotational movement satisfies a safety criteria.

The invention is based on the insight that by using an accelerometer unit, a reliable and senistive safety stop of unwanted rotational movement of the floor treatment device is achieved. For example, during a malfunction of the floor treatment device, a spinning or rotational movement of the floor treatment chassis may accidentaly originate which may result in a hazardous rotational movement of a handle member or a handle grip connected to the chassis. Such a hazardous rotational movement of the handle member or handle grip, i.e. the handle member interconnects the handle grip with a chassis portion near the engine, needs to be stopped. According to the invention, by using an accelerometer unit a reliable and sensistive satefy stop mechanism is achieved resulting in an immediate stop of floor treatment device, i.e. an immediate stop of the engine driving the floor treatment device.
In one embodiment the floor treatment device further comprises a handle member connected to said chassis, and wherein said accelerometer unit is mounted to said handle member for monitoring the rotational movement thereof. Thereby, a more significant or distinct monitor signal representing the rotational movement may be obatined. Alternatively, the accelerometer may be mounted on a handle grip, which in turn is connected to the handle member.
In one embodiment said said accelerometer unit is mounted on an outer portion on said handle member for monitoring the rotational movement thereof. Thereby, an even more significant or distinct monitor signal representing the rotational movement may be obtained.
According to an embodiment of the present invention, said controller is adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal S1, or first stop control signal, if said threshold value of said rotational movement has been reached or exceeded. Thereby, the controller is adapted to receive a monitor signal from the accelerometer unit and adapted to compare the monitor signal with the safety critera, which in this case is a threshold value. The controller is further adapted to generete the stop control signal S1, or first stop control signal S1, if said threshold value of said rotational movement has been reached or exceeded. The stop control signal S1, or first stop control signal S1, is adapted to stop motion of said floor treatment device, i.e. the engine is adapted to stop when the stop control signal S1, or first stop control signal S1, is received.
According to an embodiment of the invention, said controller is adapted to compare said monitored rotational movement with a stop interval and adapted to generate a stop control signal S1, or first stop control signal S1, if a rotational movement value matches or equals at least one value within the stop interval. Thereby, the controller is adapted to receive a monitor signal from the accelerometer unit and adapted to compare the monitor signal with the safety critera, which in this case is an interval of values. The controller is further adapted to generete a stop control signal S1, or first stop control signal S1, if said rotational movement value of said rotational movement is within the stop interval. The stop control signal S1, or first stop control signal S1, is adapted to stop motion of said floor treatment device, i.e. the engine is adapted to stop when the stop control signal S1, or first stop control signal S1, is received.
In one embodiment said controller is adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal S1 if said monitored rotational movement is above said threshold value during a period of time T. Thereby, any noise or disturbing signal may be filtered such that a more reliable rotational movement signal may be obtained.
According to an embodiment of the present invention, said controller or stop control signal S1 is configured to stop or disconnect said connectable engine from driving said floor treatment device. Thus, said controller is configured to stop or disconnect said connectable engine from driving said floor treatment device. Alternatively, said stop control signal S1 generated from the controller is configured to stop or disconnect said connectable engine from driving said floor treatment device, i.e. the engine is adapted to receive a stop signal S1 that stops the engine and thereby the floor treatment device.
In one embodiment said threshold value comprises a union of an X-component acceleration value (Xacc) and an Y-component acceleration value (Yacc), wherein the X-component acceleration value (Xacc) represents an acceleration in a direction parallel with the handle member and the Y-component acceleration value (Xacc) represents an acceleration in a tangential direction of the rotational movement of the handle member.
In one embodiment the duration of said period of time (T) is 0-150 ms.
In one embodiment the floor treatment device further comprises a dead man's handle, wherein said dead man's handle is adapted to stop motion of said floor treatment device when said said dead man's handle is released. Thereby, a more reliable and improved safety mechanism is achieved. The dead man's handle is arranged in parallel with said accelerometer unit relative to the engine. Thus, according to an embodiment of the invention, there is provided double safety system comprising a first and a second safety device. The first safety device comprises an accelerometer unit and a controller connected to each other and to the chasssi of the floor treatement device, wherein the second safety device, i.e. the accelerometer unit and the controller, is adapted to stop motion of said floor treatment device when said rotational movement satisfies a safety criteria. The second safety device comprises the dead man's handle.
In one embodiment said dead man's handle is adapted to generate an additional or second stop control signal S2 configured to stop or disconnect said connectable engine from driving said floor treatment device when said dead man's handle is released. Thereby, a more reliable and improved safety mechanism is achieved. The dead man's handle is arranged in parallel with said accelerometer unit relative to the engine. Thus, according to an embodiment of the invention, there is provided double safety system comprising a first and a second safety device. The first safety device comprises an accelerometer unit and a controller connected to each other and to the chassis of the floor treatment device, wherein the second safety device, i.e. the accelerometer unit and the controller, is adapted to generate a first stop signal S1 configured to stop or disconnect said connectable engine from driving said floor treatment device when said rotational movement satisfies a safety criteria. Whereas, the second safety device, i.e. the dead man's handle, is adapted to generate a stop control signal S2 configured to stop or disconnect said connectable engine from driving said floor treatment device when said dead man's handle is released. In other words, the engine is adapted to independently receive the first and the second stop signal. The first stop signal S1 and second stop signal S2 are thus arranged in parallel, i.e. the first and second safety system are functionally coupled in parallel relative to the engine, such that the engine may be stopped if at least one of the first and second stop control signals are generated.
In one embodiment said floor treatment device is a trowel, e.g. a walk behind trowel or steerable trowel (controlled by an operator sitting thereon).
In one embodiment said method further comprises:

setting said threshold value comprising a union of an X-component acceleration value (Xacc) and an Y-component acceleration value (Yacc), wherein the X-component acceleration value (Xacc) represents an acceleration in a direction parallel with the handle member and the Y-component acceleration value (Xacc) represents an acceleration in a tangential direction of the rotational movement of the handle member.

In one embodiment said method further comprises:

generating said stop control signal S1 if said rotational movement is above said threshold value during said period of time T.

In one embodiment said method further comprises:

setting the duration of said period of time T to 0-150 ms.

In one embodiment said method further comprises:

providing a dead man's handle;
generating a stop control signal S2 configured to stop or disconnect said connectable engine from driving said floor treatment device when said said dead man's handle is released.

In one embodiment said method further comprises:

providing a controller adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal S1 if said threshold value of said rotational movement has been reached or exceeded.

The invention will now be described in detail with reference to the drawings.

SHORT DESCRIPTION OF THE APPENDED DRAWINGS

Figure 1 a shows a perspective view of a floor treatment device comprising a floor treatment device comprising an emergency stop device, according to one embodiment of the present invention.
Figure 1 b shows a detail, of the floor treatment device shown in Figure 1 a, illustrating an accelerometer unit, according to one embodiment of the present invention.
Figure 2a shows a perspective view of a floor treatment device comprising an emergency stop device comprising an accelerometer unit and a dead man's handle, according to one embodiment of the present invention.
Figure 2b shows a detail, of the floor treatment device shown in Figure 2a, illustrating an accelerometer unit, according to one embodiment of the present invention.
Figure 3 shows a block scheme schematically illustrating the emergency stop device according to one embodiment of the present invention.
Figure 4 shows a block scheme schematically illustrating an emergency stop system according to one embodiment of the present invention.
Figure 5 shows a perspective view of the floor treatment device according to one embodiment of the present invention.
Figure 6 shows a block scheme schematically illustrating a method in the floor treatment device according to one embodiment of the present invention.
Figure 7 shows a block scheme schematically illustrating a method in the floor treatment device according to another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention is in the following mainly described with reference to a floor treatment device, more specifically a trowel having a guard member attached. The present invention relates in particular to an emergency stop device for such a floor treatment device driven by an engine. The guard member is mainly described with reference to a substantially circular structure. It should be noted that this by no means limits the scope of the invention, which is equally applicable to other floor treatment devices such as for example polishers, cleaning devices and the like, and to guards designed in any other suitable form such as for example an elliptic form.
In order to meet current machinery directive for safety features on new models of trowels, the trowel according to the present invention, is provided with an emergency stop device or system that will prevent the handle member 41 from rotating more than 270° if the handle member, and its handle grip 44 attached thereto, is released unintentionally. The emergency stop device and system are adapted to control the main engines 40 off and on function.
In one embodiment, in order to detect an undesired rotation which occurs when the user releases the handle member 41, the floor treatment device 1 is provided with an accelerometer unit 11. The accelerometer unit 11 measures the acceleration a handle member 41 is subject to when it rotates about the center of rotation, i.e. a chassis 6 comprising a motor 40. When the handle member 41 starts rotating, the handle member 41 accelerates in a first direction of rotation. This acceleration is dependent on the rotor blade friction against the surface and its rotational speed. Furthermore, the acceleration is dependent on the distance D from the accelerometer unit 11 to the center of rotation, i.e. the chassis 6 provided with the motor 40. When the handle member 41 speed increases over time, the centripetal force grows with the square of the angular velocity and proportional to the distance D to the center of rotation, and when this signal is sufficiently large, in relation to noise levels, rotation is detected.
The sensor used is an accelerometer unit 11 which should be placed as far away from the chassis 6, i.e. the centre of rotation, as possible to have the greatest leverage on the movement. In this case as close to the user as possible, i.e. at the handle member 41 close to a grip or handle grip 44, or at the grip 44. A controller 12 is coupled to the accelerometer unit 11 and continuously measures and calculates a acceleration value. When the controller 12 registered a sufficiently high value, i.e. when the acceleration is above a threshold value or within an interval, then a time period starts to be measured in order to determine for how long time the value remains above the threshold value. If the time period T reaches or exceeds a maximum value, i.e. the rotation has been continuously in one direction, the ignition system to the engine is shorted and the engine stops. However, as is understood, the controller may generate a control stop signal when the threshold value is reached or exceeded, i.e. without a time parameter.
The floor treatment device will now be described in greater detail with reference to Figure 1 a. Figure 1 a shows a perspective view of a floor treatment device 1, in this case a trowel, driven by an engine 40 and comprising an emergency stop device (as described below with reference to Figure 3) adapted to stop or disconnect the engine 40 from driving the floor treatment device 1 in case of an emergency. The floor treatment device 1 has a rotatable floor treating member 2, according to one embodiment of the present invention. The rotatable floor treating member 2, in this case comprises finishing blades. Further, the floor treatment device comprises an engine 40, a handle member 41, a handle support bar 42, a knob 43 and a grip 44 for the operator to hold on to and a protective frame 45. The length of the handle member 41, and thus the height of the grip 44, is adjustable in a telescopic manner, and the handle member 41 may be fixed at a desired length using the knob 43. The term trowel will be used with reference to the floor treatment device 1. The skilled person realizes that all of the described embodiments are just as applicable to any other type of floor treatment device having a rotating floor treating member.
Figure 1 a further shows the guard member 4 covering the rotatable floor treating member 2. The guard member 4 in the embodiment shown in Figure 1 a comprises a plurality of struts 5 connecting the guard to the chassis 6 of the trowel 1, an inner structure 7 in the form of a ring, and an outer structure 8 in the form of an annular support. The outer structure, or annular support, 8 is partly covered by the contacting element in the form of an outer ring 9. The guard member 4 is preferably attached to the chassis 6 of the trowel 1 in such a way that no relative movement is allowed between the guard member 4 and the chassis of the trowel. I.e., the guard member may be said to be fix in relation to the chassis of the trowel. The outer structure 8 is arranged circumferentially around the trowel 1. However, as an obvious constructional variation, the guard member 4 may be rotatable in relation to the chassis 6 of the trowel 1. The floor treatment device 1 further comprises an accelerometer unit 11 adapted to monitor a rotational movement of the floor treatment device 1. In the embodiment illustrated in Figure 1a, the accelerometer unit 11 is mounted close to the grip 44 of the trowel 1. As seen in the Figure, the accelerometer unit 11 is attached at an outer portion 46 of the handle member 41 at a distance D from the chassis 6 of the trowel 1. As mentioned above, the handle 41 is adjustable in a telescopic manner. The distance D is preferably between 900-2000mm.
Figure 1 b shows a detail illustrating the accelerometer unit 11 of the floor treatment device 1 in Figure 1 a. According to the embodiment, shown in Figure 1 b, the floor treatment device 1, e.g. a trowel 1, comprises a handle member 41 and wherein the accelerometer unit 11 is arranged at the handle member 41. The accelerometer unit 11 is attached at an outer portion 46 of the handle member 41 close to the grip 44. However, the accelerometer unit 11 may be arranged at any other suitable part of the floor treatment device 1, such as at the grip 44. The outer portion 46 is a radially outer portion of the floor treatment device 1 relative the centre of rotation.
Figure 2a shows a perspective view of a floor treatment device 1 further comprising a dead man's handle 47, according to another embodiment of the present invention. The floor treatment device 1 is a trowel driven by an engine 40 and comprises an accelerometer unit 11 and a controller 12 adapted to stop or disconnect the engine 40 from driving the floor treatment device 1 in case of an emergency. Furthermore, the floor treatment device 1, preferably the grip 44, is provided with a dead man's handle 47.
Figure 2b shows a detail illustrating the accelerometer unit 11 of the floor treatment device 1 in Figure 2a. The grip 44 comprises a dead man's handle 47 adapted to stop motion of said floor treatment device 1 when said dead man's handle 47 is released. Advantageously, if the dead man's handle 47 is prevented from being released, the motion of the trowel will still stop if a threshold value has been reached or exceeded.
In Figure 3, an emergency stop device 10 is schematically illustrated for a floor treatment device 1 driven by an engine (not shown), according to one embodiment of the present invention. The floor treatment device 1 comprises an accelerometer unit 11 adapted to monitor a rotational movement of the floor treatment device 1, and an controller 12 adapted to compare the monitored rotational movement and to stop motion of the floor treatment device when the rotational movement satisfies a safety criteria. The controller is further adapted to generate a first stop control signal S1 if a threshold value of the rotational movement has been reached or exceeded. The first stop control signal S1 is configured to stop or disconnect the engine 40 from driving the floor treatment device 1 when being applied to the engine 40. Thus, advantageously, in case of the occurrence of unwanted or uncontrolled acceleration of the floor treatment device 1, the engine 40 is prevented from driving and the floor treatment device 1 stops. The first stop control signal S1 may be an electrical signal which preferably is applied to the engine 40 and which is configured such that it switches of or stops the engine 40, or the signal S1 may be configured such that it disconnects, e.g. the drive belt of the engine 40 such that the engine 40 is prevented from driving.
Figure 4 illustrates an emergency stop system 100 for a floor treatment device 1. The floor treatment device 1 comprises a dead man's handle 47, wherein said dead man's handle 47 is adapted to stop motion of said floor treatment device 1 when said said dead man's handle 47 is released.
In the embodiment shown in Figure 4, said dead man's handle 47 is adapted to generate a second stop control signal S2 configured to stop or disconnect said connectable engine 40 from driving said floor treatment device 1 when said said dead man's handle 47 is released. The dead man's handle 47 is connected in parallell, i.e. functionally in parallel, with an emergency stop device 10, i.e. a first safety device, such that if the dead man's handle 47 is prevented from being released by any reason, the emergency stop device 10 ensures that the motion of the floor treatment device 1 stops if an emergency occurs. The emergency stop device 10 comprises a controller 12 adapted to compare the monitored rotational movement and adapted to generate a stop control signal S1 if a threshold value of the rotational movement has been reached or exceeded. The stop control signal S1 is configured to stop or disconnect the engine 40 from driving the floor treatment device 1 when being applied to the engine 40.
In another embodiment, the accelerometer unit 11 of the trowel 1 may comprise a plurality of accelerometers (not shown), each accelerometer in the accelerometer unit 11 being adapted to monitor a rotational movement of the trowel 1 independently. The controller 12 then calculates a mean value of said monitored rates of the plurality of accelerometers, and the controller 12 is adapted to compare the mean value, and is adapted to generate a stop control signal S1 if a threshold value of the rotational movement has been reached or exceeded.
Advantageously, setting the threshold value to a rotational movement value during a period of time T provides for a more reliable emergency stop device 10 and floor treatment device 1, which prevents unnecessary emergency stops of the engine of the floor treatment device 1. Since the monitored rotational movement must be above a certain threshold value during the period of time T before a stop control signal S1 is generated according to this embodiment, the engine 40 will not stop due to a sudden acceleration peak which is only temporarily.
In one embodiment, the duration of the period of time T is 0-150 ms.
In another aspect, the present invention relates to a floor treatment device 1 comprising an emergency stop device 10. Preferably, the floor treatment device 1 is a trowel, as illustrated in Figure 1a and Figure 2a. However, as also mentioned above, the floor treatment device 1 may be any other floor treatment device such as for example a polisher, a cleaning device or the like.
Figure 5 shows the floor treatment device 1 according to one embodiment. As seen in Figure 5, the floor treatment device 1 has an angle of rotation α. As mentioned above the handle member 41 is preferably prevented from rotating more than 270 ° if the handle member 41 is released unintentionally. Fig. 5 further illustrates the X- and Y-components, i.e. X_acc and Y_acc, measured by the accelerometer unit 11. A value of the rotational movement of the chassis is preferably calculated when the criteria that the X_acc is less than 0 (zero) and the Y_acc is above 0 (zero). However, as is understood, other criteras may also be used depending on the placement of the X- and Y-axis, i.e. the orientation of the accelerometer unit relative the chassis. The criteria mentioned above ensures that only values in a certain direction is taken into account when calculating the rotational movement. When the rotaional movement value is exceeding a predetermined or set value, the time when this occurs is registered as a starting time. If the value remains above the threshold value, a time period T is measured starting from the starting time. If the value remains above the threshold value in more than 150ms the criteria for stopping the motion of the floor treatment device 1 is fullfilled. If the value falls below the threshold value, the starting time is reset and a new time period T will start if the value exceeds the threshold value again.
In yet another aspect, the present invention relates to a safety method for a floor treatment device 1.
According to one embodiment, as illustrated in Figure 6, the method comprises:

providing an accelerometer unit 11, mounted on a chassis 6 of said floor treatment device 1; (a1)
monitoring an rotational movement of said chassis 6 of said floor treatment device 1 using said accelerometer unit 1; (a2)
comparing said monitored rotational movement with a threshold value of said rotational movement; (a3)
generating a stop control signal S1 if said threshold value has been reached or exceeded, said stop control signal S1 being configured to stop or disconnect said connectable engine 40 from driving said floor treatment device 1. (a4)

In another embodiment, the method further comprises:

In another embodiment, the method further comprises:

In yet another embodiment, the method further comprises:

setting the duration of the period of time T to 0-150 ms.

In another embodiment, as illustrated in Figure 7, the method further comprises:

providing a dead man's handle 47; (b1)
generating an additional or second stop control signal S2 configured to stop or disconnect said connectable engine 40 from driving said floor treatment device 1 when said said dead man's handle 47 is released. (b2)

Figure 7 illustrates that, in step b1, the dead man's handle 47 is activated and the engine 40 is started. In step s the engine is stopped. Preferably by applying a signal S1 or S2 to the engine 40.
In another embodiment said method further comprises:

providing a controller 12 adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal S1 if said threshold value of said rotational movement has been reached or exceeded.

In one embodiment said floor treatment device 1 is a trowel.
The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

A floor treatment device (1) drivable by an engine (40), said floor treatment device (1) comprising:
- an accelerometer unit (11) mounted on a chassis (6) of said floor treatment device (1) and adapted to monitor an rotational movement of said chassis (6);

- a controller (12) connected to said floor treatment device (1) and adapted to stop motion of said floor treatment device (1) when said rotational movement satisfies a safety criteria.
The floor treatment device according to claim 1, further comprising a handle member (41) connected to said chassis (6), and wherein said accelerometer unit (11) is mounted to said handle member (41) for monitoring the rotational movement thereof.
The floor treatment device according to claim 2, wherein said accelerometer unit (11) is mounted on an outer portion (46) on said handle member (41) for monitoring the rotational movement thereof.
The floor treatment device according to any one of claims 1-3, wherein said controller (12) is adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal (S1) if said threshold value of said rotational movement has been reached or exceeded.
The floor treatment device according to any one of claims 1-3, wherein said controller (12) is adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal (S1) if said monitored rotational movement is above said threshold value during a period of time (T).
The floor treatment device according to any one of claims 1-5, wherein said controller or said stop control signal (S1) is configured to stop or disconnect said connectable engine (40) from driving said floor treatment device (1).
The floor treatment device according to any one claims 4-5, wherein said threshold value comprises a union of an X-component acceleration value (Xacc) and an Y-component acceleration value (Yacc), wherein the X-component acceleration value (Xacc) represents an acceleration in a direction parallel with the handle member and the Y-component acceleration value (Xacc) represents an acceleration in a tangential direction of the rotational movement of the handle member.
The floor treatment device according to any of claims 5-7, wherein the duration of said period of time (T) is 0-150 ms.
The floor treatment device according to any one of the proceeding claims, wherein the floor treatment device (1) further comprises a dead man's handle (47), wherein said dead man's handle (47) is adapted to stop motion of said floor treatment device (1) when said said dead man's handle (47) is released.
The floor treatment device according to claim 9, wherein said dead man's handle (47) is adapted to generate an additional or second stop control signal (S2) configured to stop or disconnect said connectable engine (40) from driving said floor treatment device (1) when said said dead man's handle (47) is released.
The floor treatment device according to any of claims 1-10, wherein said floor treatment device (1) is a trowel.
Safety method for a floor treatment device (1), said method comprises:
- providing an accelerometer unit (11), mounted on a chassis (6) of said floor treatment device (1); (a1)

- monitoring an rotational movement of said chassis (6) of said floor treatment device (1) using said accelerometer unit (11); (a2)

- comparing said monitored rotational movement with a threshold value of said rotational movement; (a3)

- generating a stop control signal (S1) if said threshold value has been reached or exceeded, said stop control signal (S1) being configured to stop or disconnect said connectable engine (40) from driving said floor treatment device (1). (a4)
The method according to claim 12, wherein said method further comprises:
- setting said threshold value comprising a union of an X-component acceleration value (Xacc) and an Y-component acceleration value (Yacc), wherein the X-component acceleration value (Xacc) represents an acceleration in a direction parallel with the handle member and the Y-component acceleration value (Xacc) represents an acceleration in a tangential direction of the rotational movement of the handle member.
The method according to claim 13, wherein said method further comprises:
- generating said stop control signal (S1) if said rotational movement is above said threshold value during said period of time (T).
The method according to claim 14, wherein said method further comprises:
- setting the duration of said period of time (T) to 0-150 ms.
The method according to any one of claims 12-15, said method further comprises:
- providing a dead man's handle (47); (b1)

- generating an additional or second stop control signal (S2) configured to stop or disconnect said connectable engine (40) from driving said floor treatment device (1) when said said dead man's handle (47) is released. (b2)
The method according to any one of claims 12-16, said method further comprises:
- providing a controller (12) adapted to compare said monitored rotational movement with a threshold value and adapted to generate a stop control signal (S1) if said threshold value of said rotational movement has been reached or exceeded.
The method according to any one of claims 12-17, wherein said floor treatment device (1) is a trowel.