WO1998001017A1

WO1998001017A1 - Vegetation cutting device

Info

Publication number: WO1998001017A1
Application number: PCT/GB1997/001839
Authority: WO
Inventors: Colin Turner
Original assignee: Electrolux Outdoor Products Limited
Priority date: 1996-07-09
Filing date: 1997-07-08
Publication date: 1998-01-15
Also published as: GB2315005A; GB9614410D0; AU3453097A

Abstract

A machine for cutting vegetation comprises a vegetation cutter for cutting vegetation, a sensor element (8a) for detecting the boundary (13) between a region of cut vegetation (9) and a region of uncut vegetation (10), mounting means for mounting the sensor element such that, in use, the sensor element scans across an area of vegetation and produces a sensor signal which varies as the sensor element scans across the area of vegetation, and means for analysing the sensor signal to determine the position of said boundary.

Description

VEGETATION CUTTING DEVICE

This invention relates to a machine for cutting vegetation, and in particular to a lawnmower having a cutter for cutting grass .

A machine for cutting vegetation according to a first aspect of the present invention comprises a vegetation cutter for cutting vegetation; a sensor element for detecting grass above a threshold length; mounting means for mounting the sensor element such that, in use, the sensor element scans across an area of vegetation and produces a sensor signal which indicates the presence of vegetation above the threshold length as the sensor element scans across the area of vegetation.

It is preferred that the machine further comprises means for analysing the sensor signal to determine the position of a boundary between a region of vegetation shorter than the threshold length and a region of the vegetation longer than the threshold length. The analysing means typically is able to determine the boundary between vegetation which has already been cut (the vegetation shorter than the threshold length) and vegetation which has not yet been cut (vegetation which is longer than the threshold length). Such a machine is particularly useful where the boundary between cut and uncut grass is to be followed.

The mounting means preferably mounts the sensor element for movement across the area of vegetation, and this may be by virtue of mounting the sensor element for rotation about a substantially vertical axis. The vegetation cutter and sensor may be rotatable about the substantially vertical axis, or the sensor element may be mounted for rotation about an axis inclined forwards to the vertical so that the plane described by the sensor during rotation is lower at the front of the machine, when considering the normal direction of movement of the machine, relative to the rear. The vegetation cutter itself may form the sensor element, either by the tip of the vegetation cutter constituting the sensor element, or by the sensor element being mounted on the vegetation cutter. Where the vegetation cutter and sensor are rotatable about the same axis, the mounting means may mount the sensor element for rotation angularly spaced apart from the vegetation cutter, typically between 5° and 90° ahead of the cutter when considered in the normal direction of rotation. The sensor element is preferably mounted just above the vegetation cutter since the cutter is likely to be in contact with the grass, both cut and uncut throughout operation of the machine.

An alternative mounting means includes a track disposed on the machine to carry the sensor element across at least a part of the machine in order to achieve scanning. Another alternative is to use a helical "cylindrical type" cutter blade which is rotatable about a substantially horizontal axis such that, during rotation, only a short length of the blade is in contact with the grass, and that as the blade rotates, the length of the blade in contact with the grass scans transversely across the machine, and wherein the blade constitutes the sensor.

The sensor element is preferably a conductivity sensor which, during scanning, comes into contact with vegetation which is longer than the threshold length, but does not come into contact with vegetation which is shorter than the threshold length. The machine may require an electric circuit which comprises, in series, a sensor constituted by the sensor element; a voltage source; a load; and a ground contact; wherein said sensor signal is generated as a voltage across the load. The circuit may further comprise a voltage detector across the load. The ground contact may be constituted by one or more ground wheels, or by a track for supporting the machine above the ground. It is also possible that the ground contact be constituted by the vegetation cutter which, as it rotates, is n contact with the vegetation which has already been cut by the vegetation cutter .

The machine may also comprise means for determining the position of the sensor element during a scan so that the position of the boundary may be correctly determined. The position determining means may include a detector for detecting the sensor element as the sensor element passes a predetermined point, a timer, and calculating means for calculating the position of the sensor element on the basis of the time elapsed since the sensor element passes the predetermined point.

The machine may include a boundary indicator, which may be an audio output for generating inaudible noise indicative of an overlap which is too large or too small, or a visible display for indicating the position of the boundary and/or the size of overlap. It is preferred for the machine to be a lawnmowmg machine.

According to a second aspect of the invention, a method of operating a vegetation cutting machine comprises driving a cutter blade of the machine for cutting the vegetation; propelling the machine over the vegetation to be cut to bring the cutter blade into contact with the uncut vegetation; and repeatedly scanning across an area of vegetation using a sensor element for producing a sensor signal which indicates the presence of vegetation longer than a threshold length. The method preferably includes the step of analysing the sensor signal to determine the position of the vegetation above the threshold length, and this analysing step may determine the boundary between a region of vegetation shorter than the threshold length, and a region of vegetation longer than the threshold length, typically regions of already cut and not yet cut grass. The direction of the machine may be controlled such that the machine follows and overlaps the determined boundary.

Two forms of lawnmower, each of which is constructed in accordance with the invention, will now be described, by way of example, with reference to the accompanying drawings, in which :

Figure 1 is a sectional plan view of the first form lawnmower on a lawn;

Figure 2 is a sectional side view ot the first form of lawnmower ,

Figure 3 is a sectional plan view of the second form of lawnmower on a lawn;

Figure 4 is a sectional side view of the second form of lawnmower; and

Figure 5 is a graph showing the sensor signal during a single scan.

Referring to the drawings, Figures 1 and 2 show a lawnmower having a bar-shaped cutter blade 1 which is mounted on a shaft 2 for rotation about a vertical axis. A deck or shroud 3 surrounds the cutter blade 1 and is shaped like an inverted dish such that the deck 3 acts as a guard to prevent the blade from coming into contact with, for example, a person's foot or a tree. The deck 3 defines an open-bottomed cutting chamber 4 within which the cutter blade 1 rotates to cut the grass. The deck 3 is supported above the ground by ground wheels 5. The deck 3 supports a motor 6 which drives the shaft 2 in a clockwise direction (as viewed from above). The cutter blade 1, which is attached to the shaft 2 at a hub 7, is thus driven by the motor 6.

Also mounted on the shaft 2 at the hub 7 is a sensor bar 8. The sensor bar 8 is mounted on the hub 7 to rotate with the cutter blade 1 , but the sensor bar is mounted slightly higher than the cutter blade 1 so that it is clear of the short, already cut grass 9, but not so high that it is clear of long, uncut grass 10. The sensor bar 8 is also angularly displaced ahead of the cutter blade by about 45 degrees. The sensor bar 8 can be anywhere between 5 degrees and 90 degrees ahead of the cutter blade 1 in order that it makes contact with a narrow strip 10a of the uncut grass 10.

The sensor bar 8 is made of a plastics material and the tip 8a at one end of the sensor bar 8 is electrically conductive and constitutes a sensor element. The sensor element 8a is electrically connected via a conductor on the sensor bar 8, through the shaft 2 and motor housing to a circuit comprising a voltage source 11, a load 12 and an electrically-conductive ground wheel 5. When the sensor element 8a contacts long grass 10, the circuit is closed, and a small voltage ( the sensor signal VSE) is detected across the load 12 by a voltmeter (not shown). When the sensor element 8a is not in contact with long grass 10, no voltage is detected across the load 12. Only one end of the sensor bar 8 needs a sensor element 8a since the bar 8 rotates quickly. Thus, sufficient information is gathered by a single sensor element 8a. A modified arrangement is also possible, replacing the electrically conductive ground wheel with a normal ground wheel. The electrical connection to ground is then achieved by connecting the cutter blade to the circuit instead. The cutter blade 1 rotates and is in contact with the grass, both cut and uncut. The blade 1 brushes the top of already cut grass since the top of the already cut grass is defined by the blade during cutting, and so contact is made with the ground.

As the lawnmower advances forwards in the direction of the arrow F, the cutter blade 1 cuts grass, and the sensor 8a senses the lawn for regions of long uncut grass 10, and regions of shorter cut grass 9. Thus, as the sensor element 8a rotates, it scans the grass at the front of the mower.

The sensing of the boundary between cut and uncut grass has a number of useful applications.

Firstly, an overlap indicator can be used which indicates when a normal push-type lawnmower or operator-controlled self-propelled lawnmower is overlapping the boundary by an insufficient amount, or is not overlapping the boundary at all. In addition, such a device would normally indicate when the overlap is unnecessarily large. Such an indication would typically be an audible noise, the volume or tone of which changes depending upon how far the lawnmower is from its ideal overlap. Alternatively, a row of lights, typically LEDs , will indicate the position of the boundary and/or the size of the overlap so that an operator is able to steer the mower keeping the overlap to a minimum.

Secondly, the detected boundary can be used on a push-type mower or operator-controlled self-propelled mower which automatically steers to follow the boundary. The operator need not involve himself in the direction of the lawnmower.

Thirdly, a robotic lawnmower can use the boundary sensing so that it can follow the boundary between cut and un-cut grass without requiring the presence of a person to operate the lawnmower. Such a robotic lawnmower must steer itself in order to follow the boundary. As the lawnmower is propelled along the boundary 13 (see Figure 1) between uncut and already cut grass, the boundary 13 is detected. As explained above, the sensor element 8a senses the presence of cut 9 and un-cut 10 grass electrically by a conductivity measurement. The sensor element 8a, rotates with the cutter blade 1, but is mounted to rotate a little way ahead, and above, the blade.

As the sensor element 8a passes over already cut grass 9, it will not make contact with that grass (the height of the cut grass being defined by the lower height of the cutter blade), and no sensor signal is generated. As the sensor element 8a passes through long, uncut grass 10, contact is made, and conductivity is detected by the circuit.

An analysis circuit (not shown) is used to analyze the signal from the sensor element 8, and to determine the position of the boundary 13 between cut 9 and un-cut 10 grass .

Figures 3 and 4, show a second form of lawnmower. This lawnmower is a modification of the lawnmower shown in Figures 1 and 2, and so like reference numerals will be used for like parts and only the differences and modifications will be described in detail.

In this second embodiment, the sensor bar is omitted, and the cutter blade 1 itself acts to sense the grass. The tip 1a of the cutter blade 1 is electrically conductive and acts as the sensor element so that, as it rotates, the sensor element la does not touch the already cut grass 9, but does touch the longer uncut grass 10. Thus, the boundary 13 between un-cut and already cut grass 9 is sensed. A possible difficulty with this arrangement occurs because the top of the already cut grass 9 is at the same height as the cutter blade 1, and so the sensor element la might brush along the top of the already cut grass as the sensor element passes the rear of the machine, thus making the boundary 13 very difficult to detect. To avoid this, the axis of rotation is tilted forwards slightly to lift the height of the blade 1 at the rear of the machine.

Figure 5 shows the sensor element signal VSE generated during a single scan by the sensor element 1a, 8a of either of the two embodiments. The signal VSE shown during period A is zero and corresponds to the period of time during which the sensor element 1a, 8a passes over already cut grass 9. The signal during period B corresponds to the period of time during which the sensor element 1a, 8a passes through un-cut grass 10. The resolution of the signal VSE is such that, in places, individual grass strands can bo detected.

The important region of Figure 5 is indicated at C, which is the position of the boundary 13 between the already cut grass 9, and the un-cut grass 10. This boundary 13 must be kept within the transverse width at the cutter blade 1 so that an overlap occurs. The resolution of the sensor 1a, 8a is extremely high.

In the embodiments described above, the cutter blade 1 is arranged to rotate about a vertical axis However, according to a further embodiment (not shown), the cutter is a cylindrical cutter unit comprising two or more helical cutter blades defining a cylinder cutter, and a fixed blade, just like a "traditional" lawnmower One of the helical cutter blades is metallic and constitutes the sensor element. As the metallic helical cutter blade rotates in long, uncut grass, ust before it passes the fixed blade, a short length of the helical blade is in contact with the long grass, and the length of the helical blade which contacts the long grass moves along the helical blade as it rotates. Thus, the rotating helical blade scans transversely as it rotates, and a sensor signal is generated in the same way as in the above-described embodiments. A further embodiment (not shown) is also possible. Here, a track is located across the front of the lawnmower, on which track is mounted a carriage which moves back and forth across the front of the mower. The carriage carries the sensor element so that it is able to detect grass by scanning in the same way as described above.

In the above embodiments, an electrical conductivity sensor is described. Such a sensor has many advantages over other sensors, such as its reliability. However, other appropriate sensors are not excluded from consideration. For example, a capacitance sensor can be used. The capacitance sensor does not need to make contact with the grass since the sensor signal results from the measured capacitance between the sensor element (which forms a first capacitor plate) and the grass (which forms a second capacitor plate). The capacitance varies with the distance between plates, and hence the height of grass.

An optical sensor can also be used, this sensor sensing beam of a light which is directed downwards by a light source at the grass. The sensor measures various characteristics of the reflected light to generate a sensor signal.

Mechanical sensors can also be used, but are expensive. Such a sensor includes a scanning sensor finger which runs over the grass, and deflection of the finger up and down generating the sensor signal.

While the embodiments describe a lawnmower, the invention also applies equally well to crop harvesting machines, agricultural vegetation cutting machines, hedge trimmers, and snow clearing machines. Boundaries between harvested crops and unharvested crops, between cut and uncut vegetation, between cut and uncut regions of hedge, and between cleared and uncleared snow can all be detected in the same manner as described above.

Claims

1. A machine for cutting vegetation comprising: a vegetation cutter for cutting vegetation; a sensor element for detecting grass above a threshold length ; mounting means for mounting the sensor element such that, in use, the sensor element scans across an area of vegetation and produces a sensor signal which indicates the presence of vegetation above the threshold length as the sensor element scans across the area of vegetation.

2. A machine according to claim 1, further comprising means for analysing the sensor signal to determine the position of a boundary between a region of vegetation shorter than the threshold length and a region of vegetation longer than the threshold length.

3. A machine according to claim 2, wherein the analysing means determines the boundary between vegetation which has already been cut, and vegetation which has not yet been cut.

4. A machine according to any one of claims 1 to 3, wherein the mounting means mounts the sensor element for movement across the area of vegetation.

5. A machine according to claim 4, wherein the mounting means mounts the sensor element for rotation about a substantially vertical axis.

6. A machine according to claim 5, wherein the vegetation cutter and the sensor are rotatable about the substantially vertical axis .

7. A machine according to any one of claims 1 to 6 wherein the sensor element is mounted for rotation about an axis of rotation inclined from the vertical, s uch that the sensor element describes a plane which is lower towards the front of the machine when considered in the normal direction of movement relative to the rear of the machine .

8. A machine according to claim 6, wherein the vegetation cutter includes a tip which constitutes the sensor element.

9. A machine according to claim 6, wherein the sensor element is mounted on the vegetation cutter.

10. A machine according to claim 6, wherein the mounting means mounts the sensor element for rotation angularly spaced apart from the vegetation cutter.

11. A machine according to claim 10, wherein the sensor element is mounted between five and ninety degrees ahead of the cutter when considered in the normal direction of rotation

12. A machine according to claim 10 or 11, wherein the sensor element is mounted above the vegetation cutter.

13. A machine according to claim 4, wherein the mounting means includes a track disposed on the machine to carry the sensor element across at least a part of the machine.

14. A machine according to claim 4, wherein the vegetation cutter includes a helical blade rotatable about a substantially horizontal axis such that, during rotation, only a short length of the blade is in contact with the grass, and that as the blade rotates, the length of the blade in contact with the grass scans transversely across the machine, and wherein the blade constitutes the sensor.

15. A machine according to any preceding claim, wherein the sensor element is a conductivity sensor which, during scanning, comes into contact with vegetation which is longer than the threshold length, but does not come into contact with vegetation which is shorter than the threshold length.

16. A machine according to claim 15, further comprising an electric circuit: which comprises, in series: a sensor constituted by the sensor element; a voltage source; a load; and a ground contact;

wherein said sensoi siqnal ib generateα as a voltage across the load .

17. A machine according to claim 16, wherein the electric circuit further comprises a voltage detector across the loa .

18. A machine according to claim 16 or 17, wherein the ground contact is constituted by one or more ground wheels or a track for supporting the machine above the ground.

19. A machine according to claim 16 or 17 as depending from claim 3, wherein the ground contact is constituted by the vegetation cutter which, as it rotates, s in contact with vegetation which has already been cut by the vegetation cutter .

20. A machine according to any preceding claim, further comprising means for determining the position of the sensor element during a scan.

21. A machine according to claim 20, wherein the position determining means includes a detector for detecting the sensor element as the sensor element passes a predetermined point, a timer and calculating means for calculating the position of the sensor element on the basis of the time elapsed since the sensor element passes the predetermined point .

22. A machine according to any one of claims 2 to 21, further comprising means for propelling the machine over vegetation to be cut, and means for controlling the direction of propulsion of the machine such that the machine follows and overlaps the boundary.

23. A machine according to any one of claims 2 to 22, further comprising a boundary indicator.

24. A machine according to claim 23, wherein the boundary indicator includes an audio output for generating an audible noise indicative of an overlap which is too large or too small .

25. A machine according to claim 23, wherein the boundary indicator includes a visible display for indicating the position of the boundary and/or the size of overlap.

26. A lawn mowing machine according to any preceding claim.

27. A method of operating a vegetation cutting machine, the method comprising: driving a cutter blade of the machine for cutting the vegetation; propelling the machine over the vegetation to be cut to bring the cutter blade into contact with uncut vegetation; and repeatedly scanning across an area of vegetation using a sensor element for producing a sensor signal which indicates the presence of vegetation longer than a threshold length .

28. A method according to claim 27, further comprising analysing the sensor signal to determine the position of the vegetation above the threshold length.

29. A method according to claim 27, wherein the analysing of the sensor signal determines a boundary between a region of vegetation shorter than the threshold length, and a region longer than the threshold length.

30. A method according to claim 29, wherein the analysing of the sensor signal determines the boundary between a region of vegetation which has already been cut and a region of vegetation which has not yet been cut.

31. A method according to claims 29 or 30, further comprising controlling the direction of propulsion of the machine such that the machine follows and overlaps the determined boundary.

32. A machine for sensing the boundary between regions of material of different distances from a base plane comprising : a sensor element for scanning across the regions to be sensed, to produce a sensor signal which indicates the boundary between regions of different distances; and means for analysing the sensor signal to determine the position of the boundary.

33. A machine according to claim 32, wherein the machine is a snow clearer, and the sensor element produces a sensor signal which indicates the boundary between regions of snow which have been cleared, and regions of uncleared snow.

34. A machine according to claim 32, wherein the machine is a hedge trimmer, and the sensor produces a sensor signal which indicates the boundary between cut and uncut hedge.