TECHNICAL FIELD

The present invention relates to a magnetic collecting device adapted to be mounted to a robotic lawn mower. The magnetic collecting device may be 5 attached in a removable manner, and the width of the magnetic collecting device is less than the width of the robotic lawn mower.

BACKGROUND ART

For lawn mowing, it is getting increasingly popular to use autonomous lawn mowers to cut lawn grass. A typical robotic lawn mower is provided with a 0 body, an electric motor, one or more cutting blades, a battery and a control unit. A robotic lawn mower can e.g. be programmed to be used at different times, e.g. for times when the lawn is not used. The interval between mowing can also be programmed.

One preferred feature of a lawn mower is a low noise level. One solution to 5 obtain a low noise level is to use small and light cutting blades that are pivotably mounted on a cutting disc. Such a cutting blade resembles a thick razor blade and is intended to be replaced when worn. One advantage of small, replaceable cutting blades is that they require less energy and that they can be sharper than fixed, larger cutting blades. Another purpose of 0 using small and light cutting blades is that a cutting blade will be able to swing away if it hits an object during mowing, such as a rock or a wooden branch.

One problem with such cutting blades is that they may break when they hit a fixed or heavy object. The cutting blade may in this case break in two 5 parts, where one part may remain attached to the cutting disc and the other part may end up in the lawn. The broken off part of the cutting blade may be difficult to find and may be a danger for people and animals using the lawn. One known solution to find broken off cutting blade parts is to use a metal detector. This is a costly and unpractical solution that further is not very reliable, since the broken off cutting blade part may be relatively small. Another solution is to colour the blade with a visible colour. Since the cutting blades are made from metal, they can only be painted on the surface. The paint may be worn off, and the paint will further be discoloured by the grass. This makes it harder to find a broken off part of a cutting blade.

US 3,646,736 and US 3,084,495 disclose a cart adapted to be fixedly mounted at the front of a lawn mower. The cart is provided with magnets covering the complete width of the lawn mower, and is adapted to pick up magnetic articles that may otherwise damage the cutting blades of the lawn mower, and that may be thrown out from the lawn mower by the rotating cutting blades.

These systems may function for ordinary hand driven or riding lawn mowers, but are large, heavy and costly and are not suitable for a robotic lawn mower. There is thus room for improvements.

DISCLOSURE OF INVENTION

An object of the invention is therefore to provide a collecting device that provides a simple collection of broken off cutting blade parts. A further object of the invention is to provide a lawn mower comprising a collecting device that allows for a simple collection of broken off cutting blade parts. A further object of the invention is to provide a method for simple collection of broken off cutting blade parts.

The solution to the problem according to the invention is described in the characterizing part of claim 1 for the collecting device, in claim 13 for the lawn mower and in claim 15 for the method. The other claims contain advantageous embodiments and further developments of the collecting device. In a collecting device adapted to be attached to a robotic lawn mower, where the collecting device comprises a magnet adapted to pick up magnetic metal objects, the object of the invention is achieved in that the width of the collecting device is less than the width of the robotic lawn mower to which the collecting device is intended to be attached.

By this first embodiment of the collecting device according to the invention, a collecting device that can pick up broken off cutting blade parts from a lawn is provided, and which can also pick up other magnetic metal objects hidden in the lawn, such as nails, screws, drills, caps and jewellery. The collecting device is intended to be attached to a robotic lawn mower, and since a robotic lawn mower mows the lawn randomly, it will eventually cover the complete surface of the lawn, and will thus be able to collect all magnetic metal objects hidden in the lawn. If the collecting device is attached constantly to the robotic lawn mower, all broken off cutting blade parts will be found and collected. On a larger robotic lawn mower, it is possible to mount two or more collecting devices, e.g. on lawn mowers used for soccer fields, where the collecting device can also pick up magnetic objects that has been thrown in.

The collecting device is in one example adapted to be attached in a removable manner to the robotic lawn mower. It can in this way easily be attached to the robotic lawn mower when a cutting blade is broken off and there is a need to find the broken off cutting blade part. It is also possible to integrate a collecting device in the cover or in the wheels of the robotic lawn mower in a fixed way, e.g. by moulding or gluing. In one example, the collecting device comprises an attachment means that is used to attach the collecting device to the robotic lawn mower. The attachment means is in this example an attachment permanent magnet mounted to the cover of the robotic lawn mower. A magnetic strap lock is attached to the attachment means, and the strap of the collecting device is arranged in the strap lock. This will also allow the distance between the attachment means and the magnet to be adjusted, e.g. to the cutting height of the robotic lawn mower. The attachment means is in this example mounted in a pivotable way, such that the attachment means and thus the collecting device can rotate with respect to the cover of the robotic lawn mower. This will allow the collecting device to align with the lawn and to swing away from obstacles.

In another example, the attachment means is a knob adapted to hold the collecting device through a hole in the strap of the collecting device. The strap preferably comprises a plurality of holes, such that the distance between the attachment means and the magnet can be adjusted. Since the collecting device can pivot on the knob, the attachment means may be fixedly mounted to the robotic lawn mower.

The collecting device may be attached at the rear of the robotic lawn mower. The collecting device can in this way trail behind the robotic lawn mower, e.g. a few centimetres behind the robotic lawn mower. In this way, it is secured that the collecting device will always be in contact with the surface of the lawn. It is also possible to attach the collecting device at the front of the robotic lawn mower, if e.g. the charge station of the robotic lawn mower does not allow for a rear attachment. The magnet of the collecting device is preferably arranged in an enclosure at one end of the strap of the collecting device. The enclosure may be e.g. a small bag or an enclosure moulded from a rubber or plastic material. With a moulded enclosure, the strap is preferably also moulded in the same material. When permanent magnets are used, one or more magnets may be arranged in the enclosure. When an electromagnet is used, it is preferably arranged in an enclosure, with the connecting cables integrated in the strap of the connecting device.

BRIEF DESCRIPTION OF DRAWINGS The invention will be described in greater detail in the following, with reference to the embodiments that are shown in the attached drawings, in which

Fig. 1 shows a schematic robotic lawn mower with a collecting device according to the invention,

Fig. 2 shows a schematic collecting device according to the invention, and

Fig. 3 shows a schematic robotic lawn mower with an alternative collecting device according to the invention. MODES FOR CARRYING OUT THE INVENTION

The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims. References such as longitudinal, horizontal, vertical, right, left, front, rear etc. refer to directions of a robotic lawn mower in normal use.

Fig. 1 shows a schematic collecting device 2 according to the invention mounted on a robotic lawn mower, Fig. 2 shows a schematic collecting device, and Fig. 3 shows a schematic robotic lawn mower with an alternative collecting device. The robotic lawn mower 1 is provided with a cover 3, four wheels 4 and a cutting disc 5 that is driven by an electric motor (nor shown). The robotic lawn mower further comprises a battery (not shown) and a control unit (not shown). A plurality of cutting blades 6 are attached to the cutting disc in a pivotable and removable manner, such that a cutting blade can easily be replaced when worn or broken. An arrow shows the travelling direction of the robotic lawn mower when mowing grass. The collecting device 2 is in the shown example attached to the rear side of the robotic lawn mower 1 with an attachment means 7. An advantage of attaching the collecting device at the rear of the robotic lawn mower is that it can trail behind the robotic lawn mower, by allowing the strap to be longer than the distance between the attachment means and the surface of the lawn. The collecting device will in this way be able to follow the surface of the lawn, even if the surface is not perfectly flat.

The collecting device 2 comprises in the shown example a flexible strap 8 used to attach the collecting device to the cover of the robotic lawn mower. The distance between the attachment means 7 and the magnet 9, i.e. the effective length of the strap, can be adjusted. With a flexible strap attached to a strap lock, the length of the strap can easily be adjusted to e.g. the cutting height of the robotic lawn mower. In another example, the flexible strap is provided with a number of holes that are adapted to cooperate with an attachment means 7 comprising a knob.

The collecting device is preferably arranged in a pivotable manner at the cover of the robotic lawn mower. In one example, the attachment means comprises a circular attachment permanent magnet, where the attachment permanent magnet is mounted to the cover in a rotatable manner, e.g. by using a screw and a spacer. The attachment magnet and thus the collecting device can in this way pivot relative the cover of the robotic lawn mower. The strap lock is in this case magnetic, such that the attachment magnet and the strap lock can rotate around the attachment screw of the attachment magnet. When the attachment means comprises a knob, the collecting device can pivot through one of the holes in the strap. The attachment means can in this case be fixedly mounted to the cover of the robotic lawn mower.

In the shown example, the magnet 9 is enclosed in an enclosure 10. The enclosure may e.g. be a small sewn bag made from a textile material in which one or more magnets are enclosed, depending on the desired width of the collecting device. When a permanent magnet is used, the permanent magnet is preferably a strong magnet such as a neodymium magnet or other type of rare-earth magnet. The enclosure may comprise a single long magnet or several smaller magnets spaced apart. When an electromagnet is used, it is preferably arranged in an enclosure, with the connecting cables arranged in the strap. A typical robotic lawn mower for household use is in the range between 40 -55 cm wide. The width of a collecting device adapted for such a robotic lawn mower is preferably in the range between 4 - 10 cm. The diameter of the collecting device may be 1 -3 cm for a round collecting device. The cross section may have different shapes. The effective length of the strap of the collecting device may be e.g. 5-10 cm longer than the distance between the attachment means and the upper surface of the lawn. This length will further not be a problem if the robotic lawn mower must move backwards.

In a further embodiment, as shown in Fig. 3, the collecting device 2 is mounted directly on or in the cover of the robotic lawn mower. The collecting device could also be mounted on one or more wheels of the robotic lawn mower. The collecting device can be mounted to the cover by a screw, a rivet or by glue, or can be moulded into the cover. With a collecting device mounted directly on the cover of a robotic lawn mower, it is important to adapt the strength of the magnets to the distance between the collecting device and the lower surface of the lawn. The lower surface of the lawn is here understood as being the bearing surface of the robotic lawn mower, i.e. the surface on which the wheel rolls. The upper surface of the lawn is understood as the upper surface of the grass.

The collecting device comprises in a first embodiment one or more permanent magnets. The collecting device may also comprise an electromagnet. The electromagnet may be arranged in the enclosure and may be connected to the battery of the robotic lawn mower through a connector at the attachment means. It is also possible to integrate an electromagnet on or in the cover of the robotic lawn mower. Since an electromagnet will use some of the energy of the robotic lawn mower, it is of advantage to be able to program the robotic lawn mower to switch on the electromagnet only when required, e.g. when a broken off cutting blade part is to be found, or e.g. every month. It is also possible to program the robotic lawn mower to perform a magnetic metal pick up run without cutting the grass, which will allow the electromagnet to use more energy.

The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims. The collecting device may have any shape and may be made from any suitable material.

REFERENCE SIGNS

1 : Lawn mower

2: Collecting device

3: Cover

4: Wheel

5: Cutting disc

6: Cutting blade

7: Attachment means

8: Suspension attachment 9: Collecting magnet

10: Enclosure