Patent Description:
Ensuring food supply is the main challenge for the future of human life on planet earth. To reach for a sustainable and sufficient food supply current agricultural production systems and methods will need to go through radical changes. Arable land is limited: its effective, sustainable use is mandatory, especially as competition for use (Food, Feed, Fuel, Fibre) grows. High production costs provoke high food prices, especially critical for poor countries, and inaccurate use of seeds and agrochemicals results in high production costs and wasted resources.

Precision Farming (the accurate use of resources down to the plant as smallest individual unit) is a necessary measure to approach the mentioned challenges, but this is hard to achieve with large scale equipment (from a technical perspective as well as an economical perspective) and soil damage cannot substantially be reduced on heavy equipment due to the laws of growth (3D mass versus 2D contact area).

The answer to some of these issues is small automated driverless vehicles (robots), also known as autonomous agricultural machines (AAM's) able to operate around the clock without human surveillance. <CIT> discloses an AAM having a chassis propelled by four motorised wheels which are powered by an on-board battery pack. A drive control and guidance system controls propulsion of the vehicle. A seed reservoir carried by the chassis is in communication with a seed sorting and placement unit that dispenses seed to the ground.

<CIT> discloses an autonomous or remote controlled platform for planting. The platform has a central body for supporting multiple planting row units or other implements. The body is supported for movement over the ground on four adjustable legs, each having a driven and steerable track assembly or wheel. When mounted to the platform, the planting row units are offset relative to the legs and steerable track assemblies or wheels. Each planting row unit has a trench opener assembly, a planting unit for planting seed in an opened trench, and a non-steered closing wheel for closing the trench.

One known issue caused by seeding operations, whether that be by conventional tractor-hauled seeders or smaller autonomous seeders, is that of soil compaction which can be detrimental to the growth of plants, erosion of the land, and run-off of nutrients. Avoidance of excessive soil compaction during seeding operations is desirable.

According to a first aspect of the invention there is provided a seeding robot comprising a power supply, a frame, an opening device for creating a trench, a seed reservoir, seed dispensing apparatus configured to deposit seed in the trench from a dispense point, a pair of driven leading wheels which are laterally offset to opposite sides of the dispense point, and a trailing wheel positioned behind, and aligned on a longitudinal axis with, the dispense point; characterised in that the trailing wheel is steerable.

By positioning a single steerable trailing wheel behind and 'in line' with the seed dispense point a number of advantages are delivered. Firstly, the trailing wheel treads a footprint that, in a normal forward direction of travel, covers a different part of the ground to that of the leading wheels. In other words the trailing wheel does not generally follow the footprint of the leading wheels. By spreading the footprint of the vehicle and avoiding the occurrence of multiple wheels following the same track, ground compaction is reduced.

Secondly, the trailing wheel can provide a pressing function upon the seed trench which increases the seed to soil contact and assists in achieving uniform emergence. Pressing, or rolling, is a known part of the seeding process and is sometimes carried out by a dedicated rolling pass from a tractor and roll combination. The invention exploits the weight of the trailing wheel to apply the downward force in a targeted and favourable manner upon the closed seed trench.

Thirdly, by employing three ground-engaging wheels instead of four, as described in <CIT> for example, the number of components is reduced and the overall weight of the vehicle is reduced. This has a beneficial effect on manufacturing cost and ground compaction minimisation.

Fourthly, the three-wheel arrangement of the invention offers a more compact design which occupies less space in storage or transport for example.

Preferably a closing device is positioned behind the opening device and in front of the trailing wheel. The closing device may be a simple blade or tine arrangement carried immediately behind the dispense point. Although not preferable in most circumstances, it is envisaged that the trailing wheel may serve to close the trench without a separate closing device.

The trailing wheel is preferably mounted to the frame so as to be pivotable around an upright axis. In a preferred embodiment the trailing wheel is carried on a steering fork which is rotatably mounted to the frame on an upright steering axis. In a similar manner to the front wheel of a bicycle, the trailing wheel may be mounted on the chasses so that an axle carrying the wheel is supported on both sides from above. An upright rotation axis may be defined by a kingpin arrangement which is journaled to the frame. Advantageously, the steering fork arrangement facilitates a large range of steering angles which makes the vehicle more manoeuvrable. In turn this is beneficial for reducing ground compaction and turning in small spaces such as on headland turns.

A steering actuator is preferably provided to control a steering angle of the trailing wheel with respect to the frame.

The steerable tralining wheel may be driven by the provision of an electric drive motor for example.

The steering angle of the trailing wheel may be restricted within a steering angle range so that a footprint of the trailing wheel coincides with deposited seed. Advantageously this ensures that, during a seeding operation, the trailing wheel serves to press the closed trench above the sown seed. In one embodiment the seeding robot is alternately operable in a first steering mode in which the steering angle is restricted within a steering angle range so that a footprint of the trailing wheel coincides with deposited seed, and a second steering mode in which the steering angle is not restricted within said steering angle range. This allows for the greater steering angles to be utilised when the pressing functionality of the trailing wheel is not required, for example during turns on the headland.

Any restriction of the steering angle may be controlled by software in which an electronic controller determines limits for a steering angle range and controls the steerable wheel accordingly. Alternatively, a physical stop mechanism may be provided and which is selectively engageable to limit the steering angle range as required.

In a preferred embodiment the opening device is mounted to the frame by a four-bar linkage which comprises first and second link arms, wherein each of the first and second link arms is pivotably connected to the frame by respective first and second pivot joints, and to the opening device by respective third and fourth pivot joints which are disposed forwardly of the first and second pivot joints.

According to a second aspect of the invention there is provided a method of autonomous seeding with a seeding robot comprising opening a trench, depositing seeds in the trench from a dispense point, closing the trench and pressing the trench with a trailing wheel of the robot when operating in a straight forward direction of travel during a seeding operation; characterised in that the trailing wheel is steerable.

Further advantages of the invention will become apparent from reading the following description of specific embodiments with reference to the appended drawings in which:.

While the disclosure will be described in connection with these drawings there is no intent to limit to the embodiment or embodiments disclosed herein. Although the description identifies or describes specifics of one or more embodiments, such specifics are not necessarily part of every embodiment, nor are all various stated advantages necessarily associated with a single embodiment or all embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the scope of the invention as defined by the appended claims. Further, it should be appreciated in the context of the present disclosure that the claims are not necessarily limited to the particular embodiments set out in the description.

With reference to <FIG>, <FIG> and <FIG>, an autonomous seeding robot <NUM> comprises a power supply in the form of a battery <NUM> mounted on a frame <NUM> which is itself supported on ground engaging wheels. The robot <NUM> is operable in a forward direction of travel indicated by arrow V and includes a pair of leading wheels <NUM>, <NUM> and a single, steerable, trailing wheel <NUM> positioned behind the leading wheels <NUM>,<NUM> with respect to the forward direction of travel V.

The leading wheels <NUM>, <NUM> share a common rotation axis x<NUM> but are mounted independently to the frame <NUM> on separate hubs <NUM>', <NUM>'. Each hub <NUM>' is driven by a respective electric drive motor <NUM>, <NUM> which ultimately derives power from the battery <NUM>. Each leading wheel <NUM>, <NUM> can thus be driven independently to assist or even facilitate steering.

The trailing wheel <NUM> is steerable about and upright axis Z and is carried on a steering fork <NUM> which is rotatably mounted to the frame <NUM> about steering axis z. A hub <NUM>' of trailing wheel <NUM> is rotatably mounted to the steering fork <NUM> to permit rotation on axis x<NUM>. An electric drive motor <NUM> serves to drive the trailing wheel <NUM> and is ultimately powered by battery <NUM>.

The wheels <NUM>, <NUM>, <NUM> each comprise a tyre having a herringbone tread pattern for example. Although all three wheels <NUM>, <NUM>, <NUM> are shown and described as being powered, it is envisaged that one or more wheels may be unpowered whilst remaining within the scope of an aspect of the invention.

A steering control motor <NUM> is mounted in front of and parallel to the steering axis z above the steering fork <NUM> and is coupled to an upright kingpin <NUM> fixed to the steering fork <NUM> via spur gears (not shown) for controlling rotation thereof. Advantageously, the mounting of the single steerable wheel <NUM> in this manner allows a <NUM><NUM> turning angle around steering axis z thus delivering a highly manoeuvrable machine which can turn more or less on the spot. Furthermore, the three-wheeled arrangement of the robot <NUM> provides for a stable structure with a lower part count than four-wheeled machines.

The architecture of frame <NUM> provides an open structure for accommodating seed dispensing apparatus and an opening device which will described in more detail below. An outer part of frame <NUM> is constructed from tubular members which provide left and right side structures <NUM>,14R (<FIG>) which taper outwardly in the forward direction from a trailing wheel support portion 14a. The battery <NUM>, seed dispensing apparatus and opening device are accommodated between the left and right side structures <NUM>, 14R. The leading wheels <NUM>, <NUM> are carried outside of the left and right side structures <NUM>, 14R.

The battery <NUM> is carried between the left and right side structures <NUM>, 14R in a manner so that its shortest dimension is aligned generally fore and aft so that it can be carried between the leading wheels <NUM>, <NUM> and trailing wheel <NUM> and lower the machine centre of gravity.

An electric control unit (ECU) <NUM> sits atop the frame <NUM> above the battery <NUM> and houses a CPU <NUM>, a steering control system, and power electronics, and control electronics for the wheel motors <NUM>, <NUM>, <NUM>.

The battery <NUM> is preferably operable at <NUM> volts and has a capacity in the range of <NUM> to <NUM> kwh for example. A charging module and battery control system are integrated in the ECU <NUM>. While not shown, the charging module also contains a charging connector which can be brought into connection with off-board means for charging by automated plug-in. Alternatively, battery <NUM> may be exchangeable as a whole by respective battery changing means.

The control systems of the seeding robot <NUM> are illustrated schematically in <FIG> and include, inter alia, CPU <NUM>. The CPU <NUM> may be embodied as a custom made or commercially available processor, an auxiliary processor amongst several processors (although simplicity in component numbers is desirable for AAM), a semiconductor micro-processor (in the form of a microchip), a macro processor, one or more application specific integrated circuits (ASICS), a plurality of suitably configured digital logic gates, and/or other well-known electrical configurations comprising discrete elements both individually and in various combinations to co-ordinate the overall operation of the electronic control unit <NUM>.

The CPU <NUM> is coupled via an address and data bus <NUM> to I/O interface to an aerial <NUM> which provide one or more interfaces to a remote network or control system for a cluster or swarm of the seeding robot <NUM>. Additionally (although an additional aerial or antenna array may be used), this provides input for positioning data, for example Global Positioning System (GPS) or Global Navigation Satellite System (GNSS) data which is resolved in an on-board positioning system <NUM> to identify the current location of the AAM <NUM>.

Additionally coupled to the CPU <NUM> via data bus <NUM> are onboard storage devices represented by read-only (ROM) and random-access (RAM) devices <NUM>, <NUM>. The ROM <NUM> suitably carries the boot-up and general operational software for the AAM (for example in terms of routines to be followed when deviation from a pre-planned path is necessitated by an encountered obstruction), whilst the RAM <NUM> captures transitory data such as the location of obstacles encountered (location determined by guidance/positioning system <NUM>) and the actual location of seeds planted/deposited - for example where this departs from a pre-planned positioning due to environmental conditions and/or issues with the operation of the AAM.

When certain embodiments of the control systems are implemented at least in part as software (including firmware), it should be noted that alternatively or in addition to ROM <NUM>, the software can be stored on a variety of non-transitory computer-readable medium for use by, or in connection with, a variety of computer-related systems or methods. In the context of this document, a computer-readable medium may comprise an electronic, magnetic, optical, or other physical device or apparatus that may contain or store a computer program (e.g., executable code or instructions) for use by or in connection with a computer-related system or method. The software may be embedded in a variety of computer-readable mediums for use by, or in connection with, an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions.

When certain embodiments of the control systems are implemented at least in part as hardware, such functionality may be implemented with any or a combination of the following technologies, which are all well-known in the art: a discrete logic circuit(s) having logic gates for implementing logic functions upon data signals, an application specific integrated circuit (ASIC) having appropriate combinational logic gates, a programmable gate array(s) (PGA), a field programmable gate array (FPGA), etc..

In addition to the above-mentioned capture of AAM positional data, the AAM <NUM> may be provided with additional sensors to capture further operational machine information (e.g., tilt/yaw variations from horizontal, machine performance, battery usage etc.) which may be stored locally by the CPU <NUM> in memory <NUM> and made available by transmission via aerial <NUM> (if the device is configured also to transmit), or transferred via memory device, such as a memory stick, plugged into the AAM by the operator, or stored remotely and accessed, such as from a data structure (e.g., database) upon operator request or automatically upon detection of an event (e.g. conditions indicating failure of an individual AAM of a cluster).

Output from the CPU <NUM> provides a controlled drive signal to the three individual wheel drive motors <NUM>,<NUM>,<NUM>, or such other drivetrain mechanism as the AAM may have (e.g. independently controllable tracks instead of wheels) as well as to the meter drive motor <NUM>, which will be described in further detail below.

Returning to <FIG>, the robot <NUM> further comprises a seeding unit <NUM> which comprises several components to handle the seeds. A seed reservoir <NUM> is preferably fabricated from moulded plastic with a removable lid <NUM> having a filler hole <NUM> formed therein. The seed reservoir <NUM> receives seeds to be planted or placed. As will be understood in the context of an AAM, replenishing the reservoir may be an autonomous activity triggered when the reservoir is low/empty, with the AAM leaving its current planned planting path to go to a host vehicle at the side of the field from which the reservoir may be replenished, before returning to the planned task. Alternatively the reservoir <NUM> may be filled by hand as a manual task.

Hidden from view in <FIG>, but shown in <FIG> and <FIG>, seeding unit <NUM> also comprises a seeding meter <NUM> which is mounted below the seed reservoir <NUM> and is in communication therewith so that seeds drop by gravity from the reservoir <NUM> into the meter <NUM>. The seeding meter <NUM> takes seeds from the reservoir <NUM> and, and in a known fashion, separates them and outputs them as a sequence of individual seeds into a downwardly directed seed delivery chute <NUM>. In one embodiment the seeding meter is a meter manufactured by Precision Planting LLC branded 'vSet'. The seeding meter <NUM> is driven by an electrical meter drive motor <NUM> which is controlled by the CPU <NUM> via databus <NUM>.

The seeding unit <NUM> further comprises an opening device indicated generally at <NUM>. The opening device <NUM> serves the same function as openers provided in conventional seeders and planters and is operable to create a trench in the soil in which the metered seeds are deposited. The opening device <NUM> comprises a pair of mutually-angled coulters rotatably mounted to an opener support <NUM>. The coulters <NUM> are angled in a known manner so as to force open a trench as they are conveyed through the soil. Although described and shown as coulters <NUM>, the opening device may include other known trench opening elements such as spring tines or chisel-like devices.

The seeding unit <NUM> and especially the opening device <NUM> is mounted to the frame <NUM> by a four-bar linkage <NUM> wherein the four-bar linkage <NUM> is configured so that the opening device <NUM> is pushed from behind with reference to the forward direction of travel V which is contrast to known row unit suspension assemblies for seeders which pull the opening device. The four-bar linkage <NUM> comprises an upper link <NUM> and a lower link <NUM>.

In the illustrated embodiment the seeding unit <NUM> (including reservoir <NUM> and seeding meter <NUM>) is movable by the four-bar linkage <NUM> to move with opening device <NUM>. This places further weight on the opening device <NUM> and helps to smoothen the ride. In an alternative embodiment, seed reservoir <NUM> and seeding meter <NUM> are fixed to frame <NUM> with a flexible seed delivery chute enabling relative movement between seed meter <NUM> and dispense point <NUM>.

Best viewed in <FIG>, upper link arm <NUM> is pivotally connected to upright frame portion 14b by a first pivot joint <NUM>. Similarly, the lower link arm <NUM> is pivotally connected to the frame portion 14b by a second pivot joint <NUM> which is disposed below first pivot joint <NUM> in a spaced relationship. A forward end of upper link <NUM> is pivotally connected to the opening device support structure <NUM> by a third pivot joint <NUM>. A forward end of lower link arm <NUM> is pivotally connected to the opening device structure <NUM> by a fourth pivot joint <NUM> which is disposed below the third pivot joint <NUM> in a spaced relationship.

Together the upright frame portion 14b, opening device support structure <NUM>, and upper and lower link arms <NUM>,<NUM> form the four-bar linkage <NUM> connected by pivot joints <NUM> to <NUM>. The pivot joints <NUM> to <NUM> pivot about a horizontal axis so that movement freedom provided by the four-bar linkage <NUM> allows the opening device to be generally raised and lowered.

As seen in <FIG> the opener support <NUM> may be provided with a plurality of alternative holes <NUM> to which the forward end of lower link <NUM> can be connected to form the fourth pivot joint <NUM>. This permits the 'angle of attack' of the opening device to be adjusted depending on the conditions.

Raising and lowering of the seeding unit and thereby the opening device <NUM> is controlled by a lift actuator <NUM> which is connected between the frame <NUM> and one of the upper and lower link arms <NUM>,<NUM>, preferably the upper link arm <NUM> as illustrated. The lift actuator <NUM> is powered electrically and extends to raise the seeding unit <NUM> and retracts to lower the seeding unit <NUM>. Lift actuator <NUM> is electrically driven and self-locking in position, which is detected by an internal position sensor.

Seed is metered and deposited into the seed delivery chute <NUM> by the meter <NUM>. The seed delivery chute <NUM> dispenses the seed from a discharge opening into the trench formed by the opening device <NUM>. The point at which the seed is dispensed from the seed delivery chute will be referred to as the dispense point <NUM>.

A seed firmer <NUM> is fixed to opener support <NUM> for movement therewith and is positioned behind the opening device <NUM> and in front of the trailing wheel <NUM>. The seed firmer <NUM> is operable to press the seed into the furrow after being released from the seed dispense point <NUM> and to prevent the seed from jumping or rolling in the furrow.

An optional closing device <NUM> is fixed to the frame <NUM> on both sides and is positioned behind the opening device <NUM> and in front of the trailing wheel <NUM>. The closing device <NUM> is operable to close the trench and cover the dispensed seed. As best seen in <FIG> (with opener support <NUM>, seeding unit <NUM>, depth control means <NUM> and lift actuator <NUM> omitted for clarity) closing device <NUM> is pivotably attached to the frame <NUM> for rotation about axis 'w'. A wire rope <NUM> connects closing device <NUM> to the lower link arms <NUM> (by screws) so that closing device <NUM> is raised and lowered by actuator <NUM>. In addition an adjustable spring bias means <NUM> is provided to apply a force in a downwards direction upon the closing device <NUM>. Spring bias means <NUM> consists of spring 79a connected to closing device <NUM> and a catch part 79b with a recess 79c for connection with the opener support <NUM>. Recess 79c provides three upwardly extending groves 79d which can be engaged with a screw fixed to the opener support <NUM>. Depending on which of grooves 79d is engaged, the biasing force is changed.

Although shown as a simple blade fixed to the frame, the closing device <NUM> may alternatively comprise a tine for example.

With reference to <FIG>, <FIG>, and <FIG> depth control means <NUM> consists of a generally u-shaped support element <NUM> which is connected to opener support <NUM>. A stepper motor arrangement <NUM> is attached to upper and lower legs 100a, 100b. Stepper motor arrangement <NUM> is self-locking in position, which is detected by an internal position sensor. A stop motor 102a and upper bearing 102b (see <FIG>) of stepper motor arrangement <NUM> are fixed to the upper leg 100a. The lower bearing 102c and the position sensor 102d is fixed to the lower leg 100b.

In-between the upper and lower legs 100a, 100b, two side guide rods 102e and a threaded central rod 102f is provided. The threaded central rod 102f is rotated by fixed connection to the stop motor 102a. A threaded nut part <NUM> screwed on central rod 102f is prohibited against rotation by connection to movable stop element <NUM>. The threaded nut part <NUM> is fixed to the main body 104a by screws and bores (not shown in detail) in the main body 104a and is provided which slideable guide rods 102e. As a consequence, when threaded central rod 102f rotates, the threaded nut part <NUM> and thereby stop element <NUM> is torsion-locked and moves upwards and downwards in-between the upper and lower legs 100a, 100b of u-shaped support element <NUM>. With particular reference to <FIG>, stop element <NUM> (made of bended sheet metal parts) consists of integrally formed stop lugs 104b which are provided on both sides to contact with upwardly-oriented stop contours 14c provided by stop frame portions 14d of frame <NUM>.

Stop element <NUM> further includes a reinforcing metal sheet 104c which connects both stop lugs 104a by welding to increase stiffness.

The design enables actuator <NUM> to quickly raise or lower four-bar linkage <NUM> and components of the seeding unit <NUM> while depth control means <NUM> is provided to adjust working depth by means of stepper motor arrangement <NUM> which is slow in movement but allows precise and position controlled movement of stop element <NUM>.

<FIG> depict the four-bar linkage <NUM> and depth control means <NUM> in relation to frame <NUM> to further illustrate different example positions corresponding to different working conditions.

<FIG> shows a position in which the actuator <NUM> is fully extended to move the seeding unit <NUM> and opening device <NUM> into a raised position, generally referenced as a non-working position. The threaded nut part <NUM> and stop element <NUM> of the depth control means <NUM> is shown in a mid position (relative to upper and lower legs 100a, 100b). In this position, stop lugs 104b of stop element <NUM> are spaced from upwardly-oriented stop contours 14c provided by stop frame portions 14d.

With reference to <FIG>, <FIG>, the seeding unit <NUM> is shown in a working position, wherein the actuator <NUM> is retracted until stop lugs 104b of stop element <NUM> contact the upwardly-oriented stop contours 14c of stop frame portions 14d. As actuator <NUM> is provided with the torque limitation integrated in the actuator control, movement of four-bar linkage <NUM> and thereby the seeding unit <NUM> would stop. The working depth then depends on the relative position of threaded nut part <NUM> (and stop element <NUM>) in-between upper and lower legs 100a, 100b. In the position shown, a small working depth is adjusted as the threaded nut part <NUM> (and stop element <NUM>) is in a bottom position close to lower legs 100b.

In <FIG>, <FIG> the maximum working depth is adjusted as the threaded nut part <NUM> (and stop element <NUM>) is in a top position close to upper legs 100a.

It is envisaged that the working depth adjustment can be provided by depth control means <NUM> prior to lowering of four-bar linkage <NUM> by actuator <NUM> from a non-working position or alternatively, when the seeding unit <NUM> is in working position. Moving the stop element <NUM> during engagement of seeding unit <NUM>, especially opening device <NUM>, upwards (relative to upper and lower legs 100a, 100b) results in that the stop lugs 104b of stop element <NUM> would move away stop contours 14c of frame <NUM>. But due to the linkage design, the seeding unit <NUM> and opening device <NUM> is forced downwards into ground by the kinematics so that stop element <NUM> moves to contact stop contours 14c again. As a result, working depth would be increased. On the other hand, moving the stop element <NUM> during engagement of seeding unit <NUM>, especially opening device <NUM>, downwards (relative to upper and lower legs 100a, 100b) results in that stepper motor arrangement <NUM> would force stop element <NUM> against contours 14c so that the seeding unit <NUM> and opening device <NUM> move upwards to reduce working depth.

Under ideal and constant soil conditions this would be enough to operate the robot <NUM> for seeding purposes.

To cater for variations in soil conditions across a field, variable downforce control is provided.

With reference to <FIG> the lift actuator <NUM> is connected to the upper link arm <NUM> by a yieldable downforce regulating device <NUM>. The downforce regulating device <NUM> comprises a housing element <NUM> which is fixed to the upper link arm <NUM> by a pair of bracket arms <NUM>, <NUM>. The bracket arms <NUM>, <NUM> may be secured to the upper link arm <NUM> and the housing element <NUM> by any suitable fixing means such as bolts or welding. A slideable element <NUM> is retained by the housing <NUM> with freedom to move along an elongate axis of the housing element <NUM> within a movement range determined by retaining pin <NUM> held within an elongated slot <NUM> provided by the housing element <NUM>. A piston rod <NUM>' of lift actuator <NUM> is pivotally connected to sliding element <NUM> by pin <NUM>. A coil spring <NUM> is retained in the housing element <NUM> between an end wall <NUM> (welded to housing element <NUM>) and the sliding element <NUM>. The spring <NUM> presents a biasing force against sliding element <NUM> biasing the sliding element towards distal end of slot <NUM>.

As the opening device <NUM> is moved into a raised position (<FIG>), the lift actuator <NUM> extends and permits the spring <NUM> to expand and push the sliding element <NUM> until it reaches the distal end of travel in slot <NUM> whereupon further extension of lift actuator <NUM> raises the opening device <NUM> from the ground. When lowering the opening device <NUM> to a lowered position (<FIG>), the lift actuator is retracted until the upward force exerted by the ground surface upon the opening device <NUM> exceeds the biasing force of spring <NUM> whereupon further retraction of lift actuator <NUM> causes the spring <NUM> to compress and generate a downforce pressure. In operation therefore, the opening device <NUM> may ride over stones and hard regions by acting against the biasing force of spring <NUM>. As such, the position of pin <NUM> in the elongate slot <NUM> is proportional to the downforce applied to the opening device <NUM>.

The downforce regulating device <NUM> enables to apply a force on the opening device <NUM> independent of the actuator <NUM> which is locked in position during seeding. This enables a smooth ride and depth control.

The opening device <NUM> is pushed through the soil when in a lowered position and typically at a depth extending below the ground surface <NUM>. With reference to <FIG>, the force required to push the opening device into the ground Fvert is derived from torque balancing with the horizontal force FHoriz created by the driven ground-engaging wheels <NUM>,<NUM>,<NUM>. The depth control means <NUM> prevents the opening device <NUM> digging too deep and the getting stuck.

As the length of the upper and lower link arms <NUM>,<NUM> is limited by the overall length constraints of the robot <NUM> the angle β between the linkage and the ground should be as large as is practically possible in order to maximise the torque, resulting from force Fvert, which pushes the opening device <NUM> into ground. As shown with <FIG>, increasing angle β' would result in virtual lever arm a' being greater compared virtual lever arm a (for angle β in <FIG>). Furthermore virtual lever arm c' is reduced compared to virtual lever arm c (for angle β in <FIG>), the torque increased with constant horizontal force FHoriz would result in increased Fvert which pushes the opening device <NUM> into ground. The torque resulting from the resistance force of the soil F vert also decreases which helps to push the opening device <NUM> easier into ground. But this method is limited by the overall weight of the robot because the total weight always gets spread into a traction part and a downforce part. If the resistance of the soil gets bigger than the downforce part of the robot weight the opening device first but at the end the total robot gets pushed upwards.

As a result of the disclosed architecture better depth control quality is achieved without a requirement for a special minimum weight of the seeding unit itself, because for short time periods this mechanism transfers the vertical force with the help of the kinetic energy of the total robot to the opening device. This makes a light robot more suitable for changing soil conditions.

Furthermore, this helps to provide an optimised distribution of the traction force portion and the downforce force portion.

With reference to <FIG>, the steerable trailing wheel <NUM> is positioned behind and aligned on a longitudinal axis y (<FIG>) with the seed opener <NUM> and seed dispense point <NUM>. When travelling in a straight forward direction of travel as indicated in <FIG>, the footprint <NUM> of trailing wheel <NUM> passes over seed dispense point <NUM>. Advantageously, the trailing wheel <NUM> thereby serves as a press wheel to increase seed to soil contact and avoids the need for a further pass with a machine for pressing. As such, the weight of the robot <NUM> is utilized to perform a pressing function.

The steering of wheel <NUM> may be controlled by the CPU <NUM> so as to restrict the steering angle during a seeding operation to ensure that the footprint <NUM> thereof passes over the seed dispense point <NUM>. In a first steering mode in accordance with one embodiment the steering angle is restricted within a steering angle range, one limit of which is illustrated in <FIG>. In this first steering mode the maximum steering angle is limited to a relatively shallow steering angle ω<NUM> whereby the footprint <NUM>' of the trailing wheel <NUM> still coincides with the seed dispense point <NUM> and performs the aforementioned pressing function.

In a second steering mode in accordance with an embodiment the steering angle is either unrestricted or restricted within a steering angle range that is greater than that set for the first steering mode. Such wider steering angles may, for example, be utilised when not seeding (for example when turning on the headland) or when the press function is not essential. <FIG> shows the footprint <NUM>" of trailing wheel <NUM> for a relatively large steering angle ω<NUM> which does not coincide with the seed deposited at dispense point <NUM>.

As best seen in <FIG>, by positioning seed opener <NUM> (in longitudinal axis y) between the steerable trailing wheel <NUM> and leading wheels <NUM>,<NUM> on longitudinal axis y, when passing a curve the seed opener <NUM> drives on a radius indicated with R which is close to the longitudinal axis y and close to tangential. If the seed opener <NUM> was otherwise positioned in front of the leading wheels <NUM>,<NUM> lateral forces would increase mechanical loads on seed opener <NUM> and linkage <NUM> and reduce efficiency as lateral forces must be compensated by horizontal force FHoriz created by the driven ground-engaging wheels <NUM>,<NUM>,<NUM>.

Claim 1:
A seeding robot (<NUM>) comprising a power supply (<NUM>), a frame (<NUM>), an opening device (<NUM>) for creating a trench, a seed reservoir (<NUM>), seed dispensing apparatus (<NUM>, <NUM>) configured to deposit seed in the trench from a dispense point (<NUM>), a pair of driven leading wheels (<NUM>, <NUM>) which are laterally offset to opposite sides of the dispense point, and a trailing wheel (<NUM>) positioned behind, and aligned on a longitudinal axis (y) with, the dispense point; characterised in that the trailing wheel (<NUM>) is steerable.