GB2251536A

GB2251536A - Mowers.

Info

Publication number: GB2251536A
Application number: GB9200122A
Authority: GB
Inventors: Jonathan Turner
Original assignee: TURNER DEV Ltd
Current assignee: TURNER DEV Ltd
Priority date: 1991-01-11
Filing date: 1992-01-06
Publication date: 1992-07-15
Anticipated expiration: 2012-01-06
Also published as: GB9100609D0; GB2251536B; WO1992011750A1; EP0566620A1; GB9200122D0

Abstract

A mower has the ground clearance adjusted automatically by sensing the positions of skids (40) at opposite ends of a head carrying mowing cutters, the signals being compared with a memory and used alternately to pulse a first ram (18) controlling the angle of the head relative to the ground and a second ram (30) which lifts and lowers the head as a whole.

Description

MOWERS This invention relates to mowers of the kind comprising a cutting head arranged to cut a swathe of vegetation. This may include parts rotatable about an axis which is to be parallel to the ground, such as a flail mower or cylinder mower,or about vertical axes such as a disc mower.

When the ground is smooth and gently contoured, as on a sports field or like, the head may be provided with wheels or rollers to travel along the ground and support the head at the chosen cutting height. But when the mower is designed for use on roadside verges and the like, where the ground is much less even and where the cutting height may be substantially greater, for example of the order of several centimeters instead of a few millimeters, wheels and rollers are less satisfactory.

For such purposes it is common to mount the head on a suspension means, for example a system of arms projecting laterally of a tractor, with hydraulic rams for controlling the arm locations in terms of height, reach and angle of the cutting head. The head can then be visually positioned so as to be slightly clear of the ground and to cut at the required height.

However, the tractor operator has to drive the vehicle and control the (for example) three valves which affect the head position. Even a skilled operator is unable to exceed say 5kph (say 3mph) for a working shift.

Attempts have been made to provide automatic adjustment devices for safer and possibly faster operation. Patent GB 1,156,452 provides a single wheel or skid as a ground contacting probe, connected by a hydraulic, electric or mechanical linkage to the means for raising or lowering the head. In normal usage (according to the mentioned patent) the skid controls the flow of hydraulic fluid to a hydraulic ram which lifts or lowers the cutting head, and the head is allowed to 'float" to accommodate differences in angle, i.e. the slope of the ground relative to the vehicle. The driver then has to control the reach ram only. however, as explained by the same patentee in a later patent GB 2,129,265B the arrangements in Patent 1,156,452 have been found to be expensive and inefficient.

In said later patent 2,129,265 ground contacting probes are employed at each end of the cutting head, each probe being connected to a switch in an electric circuit and the hydraulic rams are in an hydraulic circuit including electro-hydraulic control valves in the same electric circuit: when one probe contacts the ground it causes the head angle to vary, when both probes contact the ground the head is bodily lifted, and when neither contacts the ground the head is lowered. Constant operation or "hunting" is avoided. No change is effected when both probes contact the ground lightly.

The applicants believe that the arrangements in the mentioned patent 2,219,265 suffer from the same disadvantages as in 1,156,452. The object of the present invention is to provide an improved automatic control system.

According to the invention, a mower of the kind comprising a cutting head rotatable about an axis intended to be parallel to the ground, and suspended from a boom system with means for lifting and lowering the head and for controlling the angle of said axis relative to the ground, is characterised by the provision of a ground contacting skid at each end of said head, each skid being independently pivoted relative to said cutting head axis, and a ground contacting roller extending between the skids and carried thereby, and spring means between the skids and the cutting head urging the head away from the roller, electrical means associated with each skid whereby the changes in angle of each skid relative to the head may be sensed in an electric circuit connecting said means and microprocessor means for comparing the sensed values with a memory and for sending signals to control valves to cause adjustment of height and angle of the head so as to tend to restore the sensed values to comparability with those required by the memory and maintain the head in a mid position of the spring driven movement.

Preferably the said electrical means are potentiometers.

The system will normally have the roller fully in contact with the ground and will tend to maintain both skids and roller at a constant (preset but variable) height and angle to the cutting head structure and hence maintain the head at a predetermined ground clearance and therefore height of cut. If the skid angle at one end reduces, meaning that the ground clearance at that end reduces, the signal will cause the head to tilt to restore the clearance and so on: that is, the hydraulic ram controlling the angle of the head relative to the suspended means will be adjusted to that effect. In addition, if the roller contacts the ground between the ends due to a localised protuberance, the head will similarly be raised although in this instance neither skid may contact the ground at all.

In contrast to the prior art, the invention may operate with substantially continuous adjustment to and fro, when the mower is operating on uneven ground, so as to maintain a particularly even and regular cut. The frictional drag of the skids in contacting the vegetation being cut particularly if they are pivoted on an axis transverse to the direction of movement of the tractor is unimportant in terms of power consumption, as is the rolling resistance of the ground roller which effectively carries only part of the weight of the head.

One of the skids or e.g. the end of the roller effectively controls the means (e.g. a hydraulic ram) which adjusts the angle of the cutting head relative to the ground, e.g. it lifts or lowers the end of the head remote from the tractor. The other of the skids or other end of the roller effectively controls the means (e.g.

another hydraulic ram) which lifts and lowers the head as a whole relative to the ground. Both rams may be supplied from the same pumped system. According to a feature of the invention, adjustment of position is carried out alternately, that is to say the respective ends of the ram are sensed for position and the valves supplying fluid to the control means for the respective ends are alternately supplied. Sensing and valve control may alternate at a number of times per second, so that the respective rams are pulsed with the same frequency.

Or continuous sensing may be used and alternate pulsing applied to the valves controlling the respective rams.

This is particularly useful when the hydraulic power requirements of the respective rams are quite disparate as will be the case in long reach arms systems where one ram to raise the head as a whole also has to pivot the whole of the system of arms, whereas the other ram has only to pivot the much smaller mass of cutting head relative to the arms. Such alternate pulsing and sensing may take both ends of the head uniformly towards the desired position.

Preferably further potentiometer means are provided in the pivoted joints of the boom system, and connected to the same control system. This may enable reach and height to be controlled and set to predetermined values instead of empirically.

According to a feature of the invention the cutting head is self-propelled. This is of particular value at maximum reach. Conveniently a hydraulic motor is provided on the head to drive a ground contacting roller which trails behind the head for the propulsion purposes.

Conveniently the potentiometers in the boom system are used to provide a signal analogue of reach, and drive is applied to the ground roller via a hydraulic motor on the cutting head by opening a valve in the supply system proportionately according to reach. Thus, full power drive is applied to the roller at full reach and perhaps no drive at minimum reach. But alternately, the roller may be driven only during the final part of reach extension. This feature is especially useful with arm systems arranged to slew, as described in co-pending patent application number where at maximum extension of the arms (maximum reach) power drive reduces load on the anti-slew or break out mechanism.

According to an important feature of the invention, the cutting head electric means e.g. potentiometers may be switched out of the circuit, to enable hedge topping or siding when the skids will be inoperative and possibly not in contact with the vegetation. The potentiometers in the boom system will then be used to control a constant height and reach, with the possibility of varying the height and at the same time automatically adjusting the angle of the head so as to keep the cut truly horizontal or truly vertical (or to any other preset angle).

One embodiment of the invention is now more particularly described with reference to the accompanying drawings wherein: Figure 1 is a somewhat diagrammatic perspective view of a mower in operation Figure 2 is an enlarged perspective view of the complete mower unit dissembled from the tractor; and Figure 3 is a side elevation of the mowing head unit.

The mowing head (Fig.3) is provided with for example a flail shaft on the axis 10 carrying a plurality of cutting flails which are rotated to effect the mowing operation. The head is provided with a centre bracket 12 which allows pivoting for the head to slew so that the axis 10 may extend parallel to the general length of the boom system comprising outer arm 14 and inner arm 16 and swing through substantially 180 degrees about that axis so as to face in either direction relative to the boom.

This slewing is effected by a head slewing ram located in the outer arm 14 carrying a rack engaged with a pinion carried on a shaft fast with the mowing head.

In addition, the cutting head is pivoted about a further axis and a head angling ram 18 is provided operating via swinging brackets 20 for the purpose of controlling the position of the head relative to the ground as will be seen for example in Figure 1, which illustrates the tractor driving along a road and cutting a bank which slopes upwardly from the tractor. The ram 18 is one of two rams to be controlled in order to maintain ground clearance according to the present invention.

The inner boom arm 16 is pivoted on a main king pin axis in the part 20 and a further slewing ram 22 drives a rack engaged with a pinion to turn the boom so as to extend from the nearside of the tractor as illustrated in Figure 1 to the offside of the tractor. As more particularly described in our co-pending patent application number , the boom can extend through more than 180 degrees, for example from a position 20 degrees in front of a line transverse to the length of the tractor on one side, to a line say 20 degrees in front of the same line on the opposite side of the tractor, i.e. through 220 degrees. This enables the mowing head to be visible by the driver of the tractor without it being necessary for him to turn and look in the opposite direction to that in which the tractor is travelling, whilst at the same time allowing the complete mower to be rear mounted on the tractor.

A third rack and pinion system is provided for extending the effective length of the outer arm 14 of the boom, as further described in said co-pending application.

The outer boom part 14 is pivoted effectively on the axis of the shaft 24 and driven about that axis by ram 26. The inner arm is pivoted on a transverse axis 28 and ram 30 is used to lift or lower the inner arm 16 about that axis and hence lift and lower the complete boom and the mower head. The ram 30 is the second of those required to be adjusted by the control system of the present invention.

Turning now to Figure 3, the mower head has a skid 40 at each end freely pivoted on shaft 42 which extends along the front of the mower head parallel to the axis 10, and a ground contacting roller 44 is mounted between the free ends of the skids. The roller may be connected to the skids via universal joints or tilting plummer blocks or other means to enable the skids to move independently of one another. Each skid is urged by a spring 46 so that effectively part of the weight of te mower head is carried by the spring. Potentiometers 48 are fixed to the structure of the cutting head and have parts movable by the skids so as to provide an electric signal which is an analogue of the skid position.

As previously described, the electric signals are compared with a memory via a microprocessor and valves in the hydraulic circuit are pulsed alternately to control the length of the rams 18 and 30, so as to maintain botch skids in a mid position, and hence control the ground clearance between the cutting parts of the head and the actual ground.

The reference 36, Figure 2 shows the position of a hydraulic drive motor for the shaft carrying the cutters of the mower; a similar drive motor may be positioned at the opposite end of the head with the drive to the roller 44. The drive may be controlled by the control circuit using a analogue of reach to control the hydraulic valve in the power supply to the motor.

Claims

1. A mower of the kind comprising a cutting head rotatable about an axis intended to be parallel to the ground, and suspended from a boom system with means for lifting and lowering the head and for controlling the angle of said axis relative to the ground, is characterised in the provision of a ground contacting skid at each end of said head, each skid being independently pivoted relative to said cutting head axis, a ground contacting roller extending between the skids and carried thereby, spring means between the skids and the cutting head urging the head away from the roller, electrical means associated with each skid whereby the changes in angle of each skid relative to the head may be sensed in an electric circuit connecting said means and microprocessor means for comparing the sensed values with a memory and for sending signals to control valves to cause adjustment of height and angle of the head so as to tend to restore the sensed values to comparability with those required by the memory and maintain the head in a mid position of the spring driven movement.

2. A mower as claimed in Claim 1 wherein the said electrical means are electronic position sensors.

3. A mower as claimed in Claim 1 or Claim 2 wherein further electronic position sensor means are provided in the pivoted joints of the boom system connected to the same control system to enable reach and height to be monitored, controlled and set.

4. A mower as claimed in Claim 2 or Claim 3 wherein the electronic position sensors are potentiometers.

5. A mower as claimed in any of Claims 1 to 4 wherein the head is self-propelled.

6. A mower as claimed in Claim 5 wherein the selfpropulsion is by means of a hydraulic or electric motor.

7. A mower as claimed in any of Claims 1 to 6 wherein the positions of the two ends of the cutting head are adjusted alternately.

8. A mower as claimed in Claim 7 wherein the drive roller is actuated automatically according to the reach adjustment by means of a signal analogue of reach compared with a memory and controlling the drive motor.