Patent Description:
One example of a self-propelled robotic tool is described in <CIT> which shows an articulated robotic lawn mower. Articulated robotic tools have excellent driving abilities and can operate in difficult terrain. The use of a goniometer makes it possible to feed back data relating to the relative angular positions between the first and second platforms, which facilitates steering of the robotic tool using a control unit. One problem associated with robotic tools in general is how to make them more robust and reliable.

<CIT> describes a robotic vehicle with first and second spaced apart chassis platforms, each comprising a wheel assembly. A linkage is coupled to the first and the second chassis platforms, such that the second chassis platform is rotatable relative to the first chassis platform. An electric brake is disposed proximate to a turning shaft and selectively applied by processing circuitry to resist turning. An angle sensor may be mounted proximate to the turning axis.

<CIT> describes a lawn mower with a support wheel and a wheel sensor configured to determine a position of the support wheel in relation to a housing. and Figs 8a8b illustrate a wheel sensor configured as a Hall sensor.

One object of the present disclosure is therefore to provide a more reliable articulated robotic tool. This object is achieved by means of a robotic tool as defined in claim <NUM>. More specifically, in a robotic tool of the initially mentioned kind, the link arrangement comprises a first part rigidly attached to the first platform, and a second part rigidly attached to the second platform being configured to pivot about the first part, and the goniometer arrangement comprises a magnet attached to the first part along the turning axis, and a Hall sensor arrangement attached to the second part along the turning axis. With such an arrangement, it is possible to achieve a goniometer with fully enclosed electronics, protecting the electronics from dust, moist etc. This is in contrast e.g. to arrangements where rheostats/potentiometers are used and where moist and dirt may disturb connectors and cause corrupted sensing. Therefore, the robotic working tool may become more robust during long-term use.

Typically, the Hall sensor arrangement may be enclosed in the second platform.

The second platform may be adapted to roll in relation to the first platform about a roll axis more or less perpendicular to the turning axis to allow the robotic working tool to operate in more difficult terrain. If so, the Hall sensor arrangement may be centered on or preferably within <NUM> from the roll axis to make sure that a sensor reading is given during roll conditions.

The Hall sensor arrangement may be adapted to detect lifting of the robotic tool. This may be accomplished by making the first part slidable along the turning axis, such that the magnet moves towards away from the Hall sensor arrangement if the robotic tool is lifted in the first or second platform. This makes it possible to detect lifting using the goniometer arrangement.

The self-propelled robotic tool may typically be a lawn mower.

The present disclosure relates to an articulated, self-propelled robotic tool <NUM>, as illustrated in <FIG>. In the illustrated case, the robotic tool is a lawn mower, although the robotic tool of the present disclosure may also be intended for other purposes. For instance, the present disclosure may also be useful in connection with robotic tools configured as robotic vacuum cleaners, golf ball collecting tools or any other type of robotic tool that operates over a working area. Typically, such robotic tools intermittently connect to a charging station (not shown).

As the robotic tool <NUM> is articulated, it comprises a first platform <NUM> and a second platform <NUM> which are interconnected by means of a link arrangement <NUM>, <NUM>. The first platform <NUM> comprises a first wheel assembly <NUM>, in the illustrated case with two wheels (one being visible in <FIG>), and the second platform <NUM> comprises a second wheel assembly <NUM>. Although this is not necessary, it is very advantageous to provide each wheel with a motor, such that they can be driven individually.

The link arrangement with a joint <NUM> and an arm <NUM> connects the first and second platforms <NUM>, <NUM> such that one <NUM> can turn with respect to the other <NUM> at a turning axis <NUM>, which is vertical or at least has a significant vertical component (e.g. deviating less than <NUM> degrees from vertical) with regard to the surface on which the robotic tool operates, in the present case the lawn. Thus, one of first and second platforms <NUM>, <NUM> can be pivoted in relation to the other at the turning axis to different mutual angular positions.

Such an articulated lawn mower has superior maneuverability e.g. compared to a single-platform robot with two driven wheels and is capable of operating in rougher lawns. An example of a lawn mower making a sharp right turn is illustrated in <FIG>. The wheels of the first wheel set <NUM> of the first platform <NUM> may then be driven in opposite directions, while the wheels of the second wheel set <NUM> of the second platform <NUM> are driving the second platform <NUM> towards the first platform <NUM>. The result is a sharp right turn while the second platform turns about the turning axis <NUM>. In order to control the movement of the lawn mower efficiently, the movement about the turning axis could be fed back to the tool's control unit.

<FIG> shows a cross section exposing components of a link arrangement between a first <NUM> and a second <NUM> platform of an articulated robotic tool as shown in <FIG>. An arm <NUM> (cf. also <FIG>), which is fixedly connected to and projects from the first platform <NUM> reaches to a position on top of the second platform <NUM>. At this location, the arm <NUM> comprises a joint <NUM> with a shaft <NUM> which extends along the main turning axis <NUM>, where the second platform <NUM> is allowed to turn with respect to the first platform <NUM>. At one end, the shaft <NUM> is fixedly connected to the to the arm <NUM> of the first platform <NUM>, and along its length, the shaft comprises a bearing arrangement <NUM> which is connected to the second platform <NUM>. In the illustrated case, the bearing arrangement comprises two ball bearings <NUM> which are provided spaced apart along the length of the shaft <NUM>, the inner piece of each bearing <NUM> being connected to the shaft <NUM>. The outer piece of each bearing <NUM> is connected to the second platform <NUM>, which is thereby made pivotable about the shaft <NUM> and thereby about the turning axis <NUM>.

In the illustrated case, the bearing arrangement <NUM> is connected to the second platform <NUM> via a link <NUM>. The shown link <NUM> is connected to the bearing arrangement at a first end and to the second platform <NUM> at a second end. As shown, the second end can optionally be connected to the second platform in a pivotable manner with a hinge <NUM>. This makes it possible to slightly turn the first and second platforms <NUM>, <NUM> in relation to each other also along a roll axis <NUM> (also indicated in <FIG>) which means that the wheel axes of the first and second platforms <NUM>, <NUM> can be slightly inclined mutually, allowing the robotic tool <NUM> to adapt better to the terrain on which it operates.

The present disclosure relates to a goniometer arrangement configured to sense a relative angular position between the first and second platforms <NUM>, <NUM> as well as adaptation of the robotic tool's behavior based on data produced by the goniometer arrangement. By a goniometer is hereby generally meant a sensor adapted to detect an angle between two devices.

In a general link arrangement, there is provided a first part <NUM> attached to the first platform <NUM>, in this case the first part is the shaft <NUM>. A second part, in the illustrated case a top wall <NUM> of the second platform's housing is attached to the second platform <NUM>, which second part is configured to pivot about first part <NUM>.

The goniometer arrangement <NUM>, <NUM> comprises a magnet <NUM>, attached to the first part, i.e. the shaft <NUM> and on the turning axis <NUM>, and a Hall sensor arrangement <NUM>, which is attached to the second part <NUM> on or close to the turning axis <NUM>.

This means that the magnet <NUM>, typically a permanent magnet, rotates in relation to the Hall sensor arrangement <NUM> when the relative angular position between the first and second platforms <NUM>, <NUM> is changed, and this rotation can be detected by the Hall sensor. The magnet <NUM> may be arranged with its poles on an axis perpendicular to the turning axis <NUM> (cf. <FIG>), although this is not necessary.

This goniometer arrangement <NUM>, <NUM> provides the advantage that the electronic part of the sensor, the Hall sensor arrangement <NUM>, can be fully encapsulated and need not be at all exposed to the environment. This is a distinct advantage compared e.g. to goniometers comprising potentiometers where a wiper, connected to one platform, runs on a resistive track, connected to another. Such a device could quickly degrade if used e.g. in a lawn mower cutting moist grass.

<FIG> schematically shows a top view of a Hall sensor goniometer arrangement <NUM>, <NUM> according to a first embodiment. The view is seen from the top of the robotic tool along the turning axis <NUM>, and, as mentioned, the permanent magnet <NUM> is rotatable about the turning axis <NUM> and with respect to the hall sensor arrangement <NUM> (or vice versa). The Hall sensor arrangement <NUM> may comprise a printed circuit board with a number of components. In the illustrated case, the sensor is a two-dimensional sensor having one Hall element <NUM> directed along the x-axis (cf. <FIG>) and one Hall element <NUM> directed along the y-axis. This orientation is only an example, and the Hall sensor arrangement <NUM> may be capable to detect an angle as long as the elements <NUM>, <NUM> are not parallel in the horizontal plane. Turning the permanent magnet <NUM> about the turning axis <NUM> will give varying responses in the Hall elements <NUM>, <NUM>, typically sine and cosine functions corresponding to an angle between the first and second platforms <NUM>, <NUM>. This may thus be sufficient to provide a goniometer reading that can be used by the robotic tool's control unit.

<FIG> illustrate schematically a side view of a Hall sensor goniometer <NUM>, <NUM>. In principle, there may be provided a third Hall element <NUM> which is directed in the z-direction, orthogonal with the x- and y-directions, thereby providing a three-dimensional Hall sensor arrangement. While this added Hall element <NUM> does not give a response to turning about the turning axis <NUM> as such, it may still provide data that is useful under some circumstances.

For instance, if the shaft <NUM> (cf. <FIG>) tilts from the original turning axis <NUM> to a tilted axis <NUM>, this can be detected by the z-axis Hall element <NUM>. Such a tilt can result from the robotic tool moving over rough terrain which makes the first and second platforms turn mutually also about the roll axis <NUM> (cf. The detection of the tilt as well as the sensed angular position can be used by the robotic tool's control unit.

<FIG> illustrates schematically a roll of an articulated robotic tool. In this case, the second platform <NUM> rolls slightly in relation to the first platform <NUM>, which is a movement that could be registered by the three-dimensional Hall sensor arrangement of <FIG>, and this data could be fed back to the robotic tool's control unit to improve the steering of the robotic tool. In order to operate well under this condition, the Hall sensor arrangement <NUM> should be reasonably centered with respect to the roll axis <NUM> typically on the roll axis <NUM> or preferably <NUM> or less from the roll axis <NUM>. In the illustrated case, the roll axis passes through the plane of the Hall sensor arrangement <NUM> circuit board.

The distance d between the magnet and <NUM> and the part <NUM> located under the magnet and being attached to the second platform could preferably be spaced apart at least <NUM> to allow this movement.

Further, the sensor arrangement could be adapted to detect lifting of the robotic tool <NUM>. This is important in many cases. For instance, with a robotic lawn mower it is important that lift is detected e.g. to disable the very sharp rotating knives under the lawn mower to avoid injuring a user, or to detect possible attempted theft.

This could be arranged using the Hall sensor arrangement, as illustrated in <FIG>. In this case, the link <NUM> connecting the bearings <NUM> to the second platform is provided with a resilient telescopic feature <NUM> that allows the link to be elongated along the turning axis <NUM>. Therefore, as illustrated in <FIG>, if a user lifts the robotic tool holding the first platform <NUM>, the link <NUM> may expand such that the magnet <NUM> is moved away from the Hall sensor circuit <NUM>. For instance, the distance there between may increase from <NUM>. 0d to <NUM>. 75d as shown in <FIG> by lifting the robotic tool. This lowers the magnetic field sensed in both the x- and y-directions, and therefore the Hall sensor arrangement <NUM>, <NUM> may be used to sense a lift. Lifting in the second platform <NUM> could cause the magnet <NUM> to instead move towards the Hall sensor circuit <NUM>.

In general, the first part/shaft <NUM> may thus be slidable along the turning axis <NUM>, such that the magnet moves away from the Hall sensor arrangement <NUM> if the robotic tool is lifted in the first platform <NUM>.

Upon sensing the lift, the robotic tool may be configured to disable rotating knives, etc..

Claim 1:
An articulated, self-propelled robotic tool (<NUM>), comprising
- a first platform (<NUM>) comprising a first wheel assembly (<NUM>),
- a second platform (<NUM>) comprising a second wheel assembly (<NUM>),
- a link arrangement (<NUM>, <NUM>, <NUM>, <NUM>) connecting the first platform to the second platform at a turning axis (<NUM>) having a significant vertical component, such that one of said first and second platform (<NUM>, <NUM>) can be pivoted in relation to the other at said turning axis to an angular position, and
- a goniometer arrangement configured to sense said angular position, characterized by:
said link arrangement comprising a first part (<NUM>) rigidly attached to the first platform (<NUM>), and a second part (<NUM>) rigidly attached to the second platform (<NUM>) and configured to pivot about the first part, and
said goniometer arrangement comprising a magnet (<NUM>) attached to the first part at said turning axis, and a Hall sensor arrangement (<NUM>) attached to the second part at said turning axis.