WO2008155235A1

WO2008155235A1 - Controlling of a seed metering device on an agricultural machine

Info

Publication number: WO2008155235A1
Application number: PCT/EP2008/057013
Authority: WO
Inventors: Gert Gilstring; Tommy Bogren
Original assignee: Väderstad-Verken Ab
Priority date: 2007-06-21
Filing date: 2008-06-05
Publication date: 2008-12-24
Also published as: SE531711C2; SE0701531L

Abstract

The invention refers to an agricultural machine comprising at least one seed metering device (8) for metering out seeds (91) for distribution to soil over which the agricultural machine moves, which seed metering device comprises a seed metering element (803) which is adapted to transport seeds and release at least one seed at a time, in addition to which the agricultural machine further comprises an electronic control unit (451) which is adapted through controlling of the seed metering element (803) to control the speed of the seeds transported by the seed metering element (803). A detection means (455) is adapted to communicate with the control unit (451 ) and to detect seeds which are transported by the seed metering element (803), and that the control unit (451) is adapted to control the speed of the seeds transported by the seed metering element (803) at least partly on the basis of signals from the detection means (455).

Description

CONTROLLING OF A SEED METERING DEVICE ON AN AGRICULTURAL MACHINE

TECHNICAL AREA

The invention refers to an agricultural machine comprising at least one seed metering device for metering out seeds for distribution to soil over which the agricultural machine moves, which seed metering device comprises a seed metering element which is adapted to transport seeds and release one seed at a time, in addition to which the agricultural machine also comprises an electronic control unit which is adapted through controlling of the seed metering element to control the speed of the seeds transported by the seed metering element.

BACKGROUND

An agricultural machine of the type 'precision seed drill^* (Eng. planter) is moved, usually towed by a tractor, over the earth that is to be drilled, and comprises a plurality of, in the lateral direction of the machine distributed, row sowing entities, each one adapted to form a seed furrow in the direction of travel of the machine, and by means of a seed metering device to place a row of seeds in the seed furrow, In order to create good conditions for the crop and yields it is important that the seeds are placed at a constant, uniform distance from each other.

The seed metering device can comprise a case and a seed metering element, commonly circular disc-shaped, which is disposed in the case and adapted to separate two spaces in the case. The case communicates with a fan by means of which a negative pressure in one of the spaces can be provided. At use seeds are gravity-fed to the other space with a pressure that is somewhat under or equal to atmospheric pressure. Alternative solutions exist with a fan-fed positive pressure on one side of the seed metering element. The seed metering element is adapted by means of a drive device to rotate during use of the machine around a seed metering axle and is provided with a plurality of peripherally disposed, through retaining openings for uptake, by means of the pressure difference, of one seed in each retaining opening. The seed metering device displays an area through which the retaining openings pass, and in which a decrease in the pressure difference is achieved, by means of a dividing flexible wall or similar, so that the seeds are released as they are moved through the area.

A problem with known seed metering devices of this type is the occurrence of s.c. 'skips', i.e. that a retaining opening passes the seeds on one side of the seed metering element without taking up a seed, or that a seed falls away from the seed metering element before the intended release-point of the seed is reached. This means that the desired placement of seeds at a constant, uniform distance from each other is not achieved.

US4928607 describes a seed drill in which a photocell is placed under the seed metering device, wherein a by the photocell detected deviation from a desired seed distribution is used to adjust a seed-manipulating member. However this solution means an afterhand adjustment of the seed metering, which means that already existing deviations cannot be dealt with.

SUMMARY

An aim with the invention is that at sowing with an agricultural machine of the type precision seed drill to create good conditions for the crop and the yield.

Yet another aim with the invention is that at sowing with an agricultural machine of the type precision seed drill to dampen the influence of skipped seed-releases on the distribution of the seeds in the soil A further aim with the invention is that at sowing with an agricultural machine of the type precision seed drill to decrease irregularities in the distribution of the seeds in the soil.

These aims are achieved with an agricultural machine of the initially described type wherein a detection means is adapted to communicate with the control unit and to detect seeds that are transported by the seed metering element, and the control unit is adapted to control the speed of the seeds transported by the seed metering element at least partly on the basis of signals from the detection means.

The detection means, exemplified below, can be adapted to detect the presence of seeds at a seed transport area displayed by the seed metering element. The seed metering element is, as is more closely exemplified below, adapted for the seed transport to be driven by a drive unit and the control unit is adapted to control the speed of the seed transport by means of controlling the drive unit. The invention has the effect that detection occurs at transport of seeds by the seed metering element and before the release of the respective seed. The speed of the seeds transported by the seed metering element refers to a relative speed in relation to the seed metering device. Through controlling of tills speed the release of seeds by the seed metering element can be adjusted in order to compensate for irregularities at transport of seeds by the seed metering element. This contributes, at irregularities in transport of seeds by the seed metering element, to a more uniform metering rate at the soil, and thus to dampening the influence of skipped seed-releases on distribution of the seeds in the soil, so as to thereby decrease irregularities in distribution of the seeds in the soil

Preferably, a deviation from a predetermined distribution of seeds in a sequence of seeds transported by the seed metering element is determinable on the basis of at least one signal from the detection means, in addition to which the control unit is adapted, on the basis of at least one signal from the detection means, on the basis of which signal a deviation from the predetermined distribution of seeds is dβterminable, to adjust the speed of the seeds transported by the seed metering element Thereby, in cases where the seeds at transport by the seed metering element are normally arranged in a sequence, an irregularity in the transport by the seed metering element can be effectively detected and compensated through adjustment of the speed of the seeds transported by the seed metering element. As Is exemplified below, the deviation from the predetermined distribution of seeds can be determined on the basis of, in addition to the at least one signal from the detection means, the position and/or speed of the seed metering element.

Preferably the control unit is adapted, on the basis of at least one signal from the detection means, on the basis of which signal an absence of a seed in the sequence of seeds transported by the seed metering element is determinable, to increase the speed of the seeds transported by the seed metering element. Thereby a prospective distance between two seeds in the soil can be decreased or eliminated in that the increased speed of seed transport by the seed metering element decreases the time distance between release of those seeds which in the predetermined distribution of seeds are disposed immediately before and after, respectively, the position of the absent seed,

In preferred embodiments the seed metering element displays a sequence of seed retaining means, and is adapted to transport seeds each one carried by one respectively of the seed retaining means, in addition to which the control unit is adapted, on the basis of at least one signal from the detection means, on the basis of which signal an absence of a seed at a seed retaining means is detemiiπable, to increase the speed of the seeds transported by the seed metering element. Since the seed metering element displays a sequence of seed retaining means, on the basis of the positions of these in combination with a skipped seed detection signal, a reliable determination of an absence of a seed can be achieved.

Preferably the control unit is adapted, on the basis of signals from the detection means, on the basis of which signals presence of seeds at the seed retaining means is deteπninable, to control the speed of the seeds transported by the seed metering element to a normal metering speed, and after the increase In the speed of the seeds transported by the seed metering element to control the speed to the normal metering speed. As is exemplified below, that which is here referred to as the normal metering speed can vary, e.g. on the basis of the speed of the agricultural machine. Through the return to the normal metering speed after the speed increase for the seed metering, an effective compensation for a local deviation in the seed distribution can be achieved without seed metering otherwise being affected.

Preferably the seed metering element is adapted to release the seeds in a release area, and the control unit is adapted to control the speed of the seeds transported by the seed metering element so that the increased speed occurs at passage through the release area of the seed retaining means at which the absence of a seed is deierminable. Since detection of seeds occurs before the release area, this means that the compensating speed occurs at a point in time that is advantageous for the seed distribution in the soil, namely when the seed retaining means that, is lacking a seed is passing through the release area. Suitably, the control unit is adapted to control the speed of the seeds transported by the seed metering element so that the normal metering speed occurs at passage through the release area of a seed retaining means which in a seed transport direction is disposed immediately before the seed retaining means at which the absence of a seed is detemrsinable.

Preferably the control unit is adapted, on the basis of signals from the detection means, on the basis of which signals presence of seeds at the seed retaining means is deterrainabie, to control the speed of the seeds transported by the seed metering element to a normal metering speed, in addition to which the speed of the seeds transported by the seed metering element, at their increased speed, is at most twice the normal speed. Such a speed adjustment contributes, at a distance from the release area to the soil of at least 0.3 metre, to an essentially more even distribution of seeds in the soil. An especially advantageous effect on the seed distribution in the soil occurs at a distance from the release area to the soil of approx. 0.5 metre and a controlling such that the speed of the seeds transported by the seed metering element at their increased speed, is approx. 1.7 times the normal speed.

In certain embodiments the maximum speed of the seeds transported by the seed metering element can be somewhat lower in order to decrease the accelerations at movement of the seed metering element. E.g. at a distance from the release area to the soil of approx. 0.5 metre, the speed of the seeds transported by the seed metering element, at their increased speed, can be 1.3- 1.5 times the normal speed.

Preferably the seed metering element is adapted to release the seeds in a release area, and the control unit is adapted to control the speed of the seeds transported by the seed metering element so that a first elevated speed occurs at passage through the release area of a seed retaining means which in the seed transport direction is disposed immediately after the seed retaining means at which the absence of a seed is determinable. Thereby the seed that is released after the skipped seed release conies to move towards the soil at a higher speed man the seed that is released before the skipped seed release, which contributes to decrease the distance between these seeds in the soil and to compensate for the prospective irregularity in metering due to the skipped seed release. This contribution to the compensation, which consists of a higher release speed for the seed which is released after the skipped seed release so that this 'catches up a bit' with the preceding seed, makes it possible to decrease a contribution to the compensation which consists of a decreased time gap between the seed release on each side of the skipped seed release. This in its turn makes it possible to decrease the accelerations at movement of the seed metering element, which in its turn decreases the risk of additional 'skips'.

The control unit can furthermore be adapted to control the speed of the seeds transported by the seed metering element so that a second elevated speed, which is lower than the first elevated speed, occurs at passage through the release area of a seed retaining means which in the seed transport direction is disposed immediately after the seed retaining means which is disposed immediately after the seed retaining means at which the absence of a seed is determinate. Thus the speed is gradually decreased after the passage through the release area of the seed retaining means which is disposed immediately after seed retaining means at which the absence of a seed is determinable, so that subsequent seed retaining means also pass through the release area at an elevated speed. As is exemplified below, through such a gradual decreasing of the speed a very good compensation of the seed distribution can be achieved despite the skipped seed release.

Preferably the seed metering element is adapted to rotate around a seed metering axle and to transport the seeds at a distance from the seed metering axle, and the control unit is adapted to control the transport speed of the seeds through controlling the rotational velocity of the seed metering element. The seed metering element is thereby adapted to rotate around the seed metering axle by means of the mentioned drive unit, and the control unit is adapted to control the rotational velocity of the seed metering element through controlling the drive unit.

DRAWINGS SUMMARY

Embodiments of the invention will be described in detail below with reference to the drawings, in which

- Fig. 1 shows a perspective view of a precision seed drill, seen obliquely from above and obliquely from the rear, according to an embodiment of the invention,

- Fig. 2 shows a perspective view of a row sowing unit that is a part of the precision seed drill in Fig. 1,

- Fig, 3 shows a perspective view of a section vertical and parallel to the direction of travel of the precision seed drill of a seed metering device that is a part of the row sowing unit in Fig, 2, a drive device for the seed metering device, and an electronic control unit, - FIg, 4 is a schematic cross-sectional view of the seed metering device, with the cross-section lying along the line IV-IV in Fig. 3. - Fig. 5 is a schematic cross-sectional view of the seed metering device, with the cross-section lying along the line V-V in Fig. 4,

- Fig, 6 is a diagram which shows signals from a detection means at the seed metering device in Fig. 3, - Fig. 7 shows a part of a seed metering element in the seed metering device in Fig. 3, and

- Fig. 8 is a diagram that shows the rotational velocity of the seed metering element in Fig. 7,

- Fig. 9 is a diagram that shows exit speeds for seeds at release from a seed metering element, at a special speed controlling of the seed metering element, and

- Fig. 10 shows a iable which contains values regarding seed distribution at the speed controlling in Fig. 9.

DETAILED DESCRIPTION

Fig. 1 shows a perspective view of an agricultural machine in the form of a precision seed drill 1 according to an embodiment of lhe invention. The precision seed drill comprises a number, in this example eight, row sowing entities 2, each one fastened on a structural member 3 comprising a cross-running steel beam. The structural member 3 forms a part of the frame of the machine which is carried by two carrying wheels 3 a. The precision seed drill is, by means of a fastening member 5 arranged at at least one free end of a longitudinal structure detail 4, adapted to be coupled behind a draught vehicle and brought in a direction indicated by the arrow F in Fig, 1 , Each one of the row sowing entities 2 is adapted at movement of the machine 1 over the earth that is to be sown to create a seed furrow in the direction of travel of the machine, to place one seed at a time along the seed furrow in order to create a row of seeds in the direction of travel F of the machine, and to close the seec ig. 2 shows one of the row sowing entities 2 in Fig. 1. This is by means of a linkage device 6 connected with the cross -running structural member 3. The linkage device 6 forms a parallelogram structure so that the row sowing unit 2 can move vertically without rotation in relation to the structural member 3.

The row sowing unit 2 comprises a seed container 7 which communicates with a below more closely described seed metering device 8, adapted via a distribution member (not shown) to distribute one seed at a time to a seed furrow In the soil. Alternatively the agricultural machine can display one or several seed containers, each one of which communicates with a plurality of seed metering devices.

The row sowing unit 2 comprises a seed furrow forming means, comprising two rotatable discs 10 and adapted to form the seed furrow. The discs 10 are at use of the machine adapted during rotation to partly intrude into the soil, wherein a lower orifice on the distribution member rurming from the seed metering device 8 is disposed immediately behind the intrusion of the discs 10 into the soil. The row sowing unit 2 is adapted to be carried by two support wheels 1 1 , disposed on each side of the pair of discs 10. The sowing depth is adjustable according to known technique through adjustment of the height of the support wheels ! 1 in relation to the discs 10. The row sowing unit 2 in this example also comprises here not more closely described after-cultivating members 202, adapted to close the seed furrow.

Fig. 3 shows a perspective view of a section, vertical and parallel to the direction of travel of the precision seed drill, of the seed metering device 8. This comprises a cylindrical case 802 and a from the case downward directed seed metering pipe 801, which communicates with the distribution member. The seed metering device 8 also comprises a seed metering element 803, in the form of a round seed metering plate 803 which is arranged essentially concentrically in the case 802,

As can be seen in Fig. 4 the seed metering plate 803 is adapted to separate a first and a second space 821 , 822 in the case 802. At use seeds 91 are gravity-fed from the seed container 7 (Fig, 2) into the case 802 on one side of the seed metering plate 803, in this example in the first space 821 disposed on the left side of the seed metering plate 803 viewed in the intended direction of travel F of the agricultural

The seed metering plate 803 is adapted to rotate in its plane around a primarily horizontally orientated seed metering axle 805, as is indicated in Fig. 3 by the arrow R. This rotation is performed by means of a drive device, comprising a with the seed metering axle 805 and the seed metering plate 803 connected drive unit 401 in the form of an electric or a hydraulic motor which is fixedly connected with the seed metering device 8. (in Fig, 3 the drive unit 401 is shown for the sake of the presentation somewhat displaced from the seed metering device 8.)

As can be seen in Fig, 3 the agricultural machine comprises an electronic control unit 451 , and a speed determining means 452 adapted to send to the control unit 451 signals which indicate the speed of the agricultural machine. The speed determining means 452 is in this embodiment provided in the form of a radar directed towards the soil, but can alternatively be provided as a pulse transmitter arranged at a cogwheel or similar which is fixedly connected with and concentric with one of the carrying wheels 3a (Fig. 1), or in the form of a speed meter at the draught vehicle for the agricultural machine, wherein signals which correspond to the speed are conducted in a suitable way from the draught vehicle to the control unit 451 , The control unit 451 is adapted to control the drive unit 401 on each one of the row sowing entities 2 at least partly on the basis of the signals from the speed determining means 452. More precisely, on the basis of the signals from the speed determining means 452 the drive unit 401 is controlled so that the speed of the drive unit 401 speed increases at an increase in the speed of the agricultural machine, and vice versa. This machine speed-dependent speed for the seed metering is in this embodiment that which in this presentation is termed normal metering speed. Alternatively several control entities 451 can be provided, each one for one or a proportion of the seed metering devices 8. As can be seen in Fig. 1 the agricultural machine ! comprises an air pressure device comprising a fan 501 and, communicating with the fan, air pipes 502, each one extending to one respectively of the seed metering devices 8, As can be seen in Fig, 4 the case 802, more precisely the second space 822, communicates at the respective seed metering device 8 with the respective branch pipe 502. The fan 501 is adapted to provide a negative pressure in the branch pipe 502 and in the second space 822, which gives rise to a pressure difference between the first and the second space 821 , 822,

As is apparent in Fig, 3 the seed metering plate 803 is adapted to transport seeds and release one seed at a time down towards the seed furrow. More precisely the seed metering plate 803 is adapted to in a circular, with the seed metering axle 805 concentric, seed transport area 806 at a distance from the seed metering axle 805, take, transport and release seeds. The seed metering plate 803 displays in the seed transport area 806 a plurality of seed retaining recesses 804 formed by respective through retaining openings 804 disposed at the same radial distance from the seed metering axle 805, in this example in the vicinity of the periphery of the seed metering plate 803, which retaining openings 804 are distributed at equal distance from each other in the circumference of the seed metering plate 803. Through the above described pressure fall over the seed metering plate 803 a seed fastens at each retaining opening 804 and is transported towards the seed metering pipe 801. Thus the seed metering plate 803 displays a sequence of retaining openings 804, for formation of a predetermined distribution of seeds in a sequence of seeds transported by the seed metering plate 803.

The seed metering device 8 is adapted to release the seeds on one side of the seed metering axle 805 on which the seeds are transported by the seed metering plate 803 with a downward-directed speed component in relation to the seed metering axle 805. As can be seen in Fig. 5, the release of the seeds is made possible by separating means 823 comprising a wall 823, which is preferably of a flexible material. The wall 823 is disposed on the same side of the seed metering plate 803 as the second space 822 (Fig. 4). The wall 823 borders an area at which the retaining openings 804 pass. The wall 823 brings about a decrease in the pressure fall over the seed metering plate 803 so that the seeds are released as they pass into the area, Fig. 3 shows a release area SL (indicated by broken lines), in which due to the decreased pressure the seeds detach from respective retaining opening 804, and fall down through the seed metering pipe 801. Alternatively the wall 823 can be of a rigid material, wherein a slit-sealing is achieved between the wall 823 and the seed

It should be mentioned that the seed metering device 8 also comprises an in Fig. 3 shown seed singulation member 824, which in known way is adapted to detach any additional seeds at a retaining opening.

In the embodiment described e.g. with reference to Fig. 3, in which the seed metering axle 805 is primarily horizontal, the release area SL is disposed primarily in the same height position as the seed metering axle 805, so that seed transport area 806 has a maximum downward-directed speed component in the release area SL. Alternatively the release area SL can foe disposed higher or lower than the seed metering axle 805, although on a side of the seed metering axle on which the seeds are transported with a downward-directed speed component in relation to the seed metering axle.

From the description above it is evident that the mentioned control unit is adapted, through controlling of the drive unit and thereby of the seed metering plate 803, to control the speed of the seeds transported by the seed metering plate 803. As can be seen in Fig. 3 a detection means 455 is adapted to communicate with the control unit 451 and to detect seeds 91 thai are transported by the seed metering plate 803. The detection means 455 is disposed before the release area viewed in the seed transport direction, and is provided as a photodetector directed towards the seed transport area 806 for changes in signals to the control unit 451 at passage of a seed in front of the photo detector. As an alternative to photo defector, the detection means 455 can comprise a capaeitive transmitter, an ultrasound transmitter, a transmitter for laser measurement, or some other suitable member.

Fig. 6 shows an example of signals SD which are received by the control unit 451 from the detection means 455. At the time points called tF in Fig. 6, signals originate from the detection means 455, on the basis of which signals presence of seeds at the seed retaining openings 804 is determinable. The control unit 451 is adapted, partly on the basis of the signals that arise at these time points tF, to control the speed of the seeds transported by the seed metering plate to the normal metering speed. As mentioned above the seed metering plate 803 is thereby controlled so that its speed increases at an increase in speed of the agricultural machine, and vice versa.

More specifically the seed metering device 8 comprises a speed transmitter (not shown) adapted to send to the control unit signals which correspond to the angular velocity of the seed metering plate, and in this way to provide a feedback on the controlling of the angular velocity. (Alternatively the seed metering device 8 can comprise an angle transmitter (not shown), which is adapted to send to the control unit 451 signals corresponding to the angle position of me seed metering plate 803, and on the basis of the signals from the angle transmitter the angular velocity can be determined.) The control unit 451 comprises an algorithm, which, on the basis of known quantities between the seed retaining openings 804 and the angular velocity of the seed metering plate 803, can calculate the time points for passage of the seed retaining openings 804 past the detection means 455, E.g. the algorithm can, as is exemplified below, on the basis of a known distance, or angular distance, between the seed retaining openings 804 and information on the angular velocity of the seed metering plate 803 at a sequence of time points, determine a time point for a next- following passage of a seed retaining opening from a time integration of the angular velocities, If a signal from the detection means 455 which corresponds to the presence of a seed is lacking at this calculated 'arrival time', the absence of a seed in the relevant seed retaining opening can be determined,

Alternatively, in embodiments where the seed metering device 8 comprises an angle transmitter, calculated time points for passage of seed retaining openings past the detection means 455 can be determined, on the basis of signals corresponding to the angle position of the. seed metering plate 803 and information on the angular velocity of the seed metering plate 803 at a sequence of time points. Thereby, when signals from the detection means 455 corresponding to the presence of a seed are lacking, the absence of a seed in the relevant seed retaining opening can be

Thus in this example, at the time point tD (Fig. 6) the control unit receives signals from the detection means, on the basis of which an absence of a seed at a seed retaining opening 804 is determinable. On the basis of the signals at the time point tD the control unit 451 is adapted to increase the speed of the seeds transported by the seed metering plate 803.

Here reference is to Fig. 7. The control unit 451 is adapted to control the speed of the seeds transported by the seed metering plate 803, through regulating the rotational velocity ω of the seed metering plate 803, so that the increased speed occurs at passage through the release area SL of the seed retaining opening 804 at which the absence of a seed is determinable. This occurs through allowing a predetermined stretch si along the row of seed retaining openings 804 to pass the release area SL at the normal metering speed, before the speed is increased. The mentioned stretch s1 is dependent on the position of the detection means 455 in relation to the release area SL. Through this distance-adapted speed increase, the normal metering speed occurs at passage through the release area SL of a seed retaining opening 804 which in the seed transport direction is disposed immediately before the seed retaining opening at which the absence of a seed is determinahle. As can be seen in Fig. 8, at a time point tH 1 an increase is initiated in the rotational velocity ω of the seed metering plate 803 from the normal metering speed ω 1 to a compensation speed ω2. This time point tH1 can e.g. be determined from the

equation . RTF is, as shown by Fig. 7, the radial distance of the seed

metering openings 804 from the seed metering axle 805. The compensation speed can e.g. be determined as ω2 = K*ω1 where K is a constant which is greater than 1.

The control unit 451 is adapted to allow a predetermined stretch s2 (Fig. 7) along the row of seed retaining openings 804 pass the release area SL at the increased metering speed, before the speed is again controlled to the normal metering speed ω1. The time point tH2 (Fig. 8) for initiation of mis speed decrease can e.g. be

determined from the equation . Thereby the normal metering speed

ω1 occurs at passage through the release area SL of a seed retaining opening 804 which in the seed transport direction is disposed immediately after the seed retaining opening at which the absence of a seed is determinable.

As an alternative the return to the normal metering speed ω1 and/or the predetermined stretch s2 (Fig. 7) can be adapted so that the seed retaining opening 804, which in the seed transport direction is disposed immediately after the seed retaining opening at which the absence of a seed is determinable, passes through the release area SL at a speed which is higher than the normal metering speed ω 1. Thereby the seed which is released after the skipped seed release comes to move towards the seed furrow at a higher speed than the seed which is released before it, which contributes towards decreasing the distance between these seeds in the seed furrow and towards compensating for the irregularity in the metering brought about by the skipped seed release. An example of a particularly advantageous controlling of the metering speed is described here with reference to Figs. 9 and 10. As is shown in Fig. 9, the normal metering speed of the seeds in the actual operating case for the agricultural machine is 0.4 m/sec. A seed is lacking in the seed retaining opening 804 which in the transport direction is disposed after the seed (Fig. 10, 'seed-1') which is released at time 0.10 sec. The control unit thereby controls the seed metering plate 803 so that a first elevated speed for the seeds of 0.68 m/sec occurs at passage through the release area SL of a seed (Fig. 10, 'seed1') which in the seed transport direction is disposed immediately after the seed retaining opening 804 at which the absence of a seed is determined. At passage through the release area SL of an additional three subsequent seeds (Fig, 10, 'seed2' 'seed3) these display a respective second, third fourth elevated speed of 0,49, 0.42 and 0.41 m/sec, respectively, each of which is less than the preceding. At passage through the release area SL of the fifth seed (Fig. 10, 'seed5) after the seed retaining opening 804 at which the absence of a seed is determined;, the normal metering speed occurs once again,

As can be seen in the bottom row in the table in Fig, 10, at a 'skip', a complete compensation is achieved through the speed controlling shown in Figs 9 and 10 at placement of the seeds in the soil. This is achieved despite accelerations of the seed metering plate during this compensatory measure being relatively low, which reduces the risk of additional 'skips'.

Within the framework of the invention, the seed metering device 8 can be arranged in a large number of alternative ways. For example the seed metering device 8 can be orientated in alternative ways in relation to the agricultural machine, e.g. so that the seed metering element 803 extends primarily in a plane across the direction of travel of the agricultural machine.

Furthermore the pressure fall achieved by means of the fan 501 over the seed metering element 803 can alternatively be achieved with a positive pressure on one side of the. seed metering element 803 and an atmospheric pressure on the other side, Such an embodiment can be understood at a comparison with Fig. 4. In order to achieve a positive pressure in the first space 821 , to which the seeds are metered from the seed container, the air pipe 502 communicating with the fan can communicate with the first space 821 instead of, as is shown in Fig, 4, with the second space 822. Thereby the case 802 does not need to include a space on the right side of the seed metering plate 803 in Fig. 4, but this side can instead be exposed to the surrounding atmosphere.

In addition, instead of retaining openings in the form of through holes, the seed metering plate 803 can display on one side at its periphery evenly distributed deepenings, each one adapted to take up a seed, in addition to which a through recess in the base of the respective deepening by means of the pressure fall achieves a retention of the respective seed. Such a recess can be designed as a deepening in the periphery of the seed metering plate 803.

Alternatives to the pressure fall-caused uptake of seeds on the seed metering plate 803 can be provided. In one alternative the seed metering device can be arranged as what is called in English a 'finger pickup meter', in which a number of seed retaining means in the form of cam-driven 'fingers' are evenly distributed at the periphery of the seed metering plate, and each one adapted at rotation of the plate, by means of the cam control, to pick up one seed at a time in a certain area and to release the seed in another area.

In the embodiment described above the agricultural machine displays a fan 501 which communicates with all seed metering devices 8. Alternatively the agricultural machine can display one or several fans 501 each one of which communicates with one or several of the seed metering devices 8,

Claims

1. Agricultural machine comprising at least one seed metering device (8) for metering out seeds (91) for distribution to soil over which the agricultural machine moves, which seed metering device comprises a seed metering element (803) which Is adapted to transport seeds and release one seed at a time, in addition to which the agricultural machine further comprises an electronic control unit (451) which is adapted through controlling of the seed metering element (803) to control the speed of the seeds transported by the seed metering element (803), characterised in that a detection means (455) is adapted to communicate with the control unit (451) and to detect seeds which are transported by the seed metering element (803), and that the control unit (451 ) is adapted to control the speed of the seeds transported by the seed metering element (803) at least partly on the basis of signals from the detection means (455).

2. Agricultural machine according to Claim 1, wherein a deviation, from a predetermined distribution of seeds in a sequence of seeds transported by the seed metering element (803), is determinable on the basis of at least one signal from the detection means (455), in addition to which the control unit

(451 ) is adapted, on the basis of at least one signal from the detection means (455), on the basis of which signal a deviation from the predetermined distribution of seeds is determinable, to adjust the speed of the seeds transported by the seed metering element (803),

3. Agricultural machine according to Claim 2, wherein the control unit (451) is adapted, on the basis of at least one signal from the detection means (455), on the basis of which signal an absence of a seed in the sequence of seeds transported by the seed metering element (803) is determinable, to increase the speed of the seeds transported by the seed metering element (803).

4. Agricultural machine according to any one of the preceding Claims, wherein the seed metering element (803) displays a sequence of seed retaining means (804), and is adapted to transport seeds each one carried by one respectively of the seed retaining means (804), in addition to which the control unit (451) is adapted on the basis of at least one signal from the detection means (455), on the basis of which signal an absence of a seed at a seed retaining means (804) is determinable, to increase the speed of the seeds transported by the seed metering element (803),

5. Agricultural machine according to Claim 4. wherein the control unit (451 ) is adapted, on the basis of signals from the detection means (455), on the basis of which signals presence of seeds at the seed retaining means (804) is determinable, to control the speed of the seeds transported by the seed metering element (803) to a normal metering speed (ω1), and after the increase in the speed of the seeds transported by the seed metering element

(803) to control the speed to the normal metering speed (ω 1 ).

6. Agricultural machine according to Claim 4 or 5, wherein the seed metering element (803) is adapted to release the seeds in a release area (SL), and the control unit (451) is adapted to control the speed of the seeds transported by the seed melering element (803) so that the increased speed occurs at passage through the release area (SL) of the seed retaining means (804) at which the absence of a seed is determinable.

7. Agricultural machine according to Claim 6, wherein the control unit (451) is adapted to control the speed of the seeds transported by the seed metering element (803) so that the normal metering speed (ω1) occurs at passage through the release area (SL) of a seed retaining means (804) which in a seed transport direction is disposed immediately before the seed retaining means (804) at which the absence of a seed is determinable.

8. Agricultural machine according to any one of Claims 4-7, wherein the control unit (451) Is adapted, on the basis of signals from the detection means (455), on the basis of which signals presence of seeds at the seed retaining means (804) is detemiinable, to control the speed of the seeds transported by liie seed metering element (803) to a normal metering speed (ω l ), in addition to which the speed of the seeds transported by the seed metering element (803), at their increased speed, is at most twice the noπnal

9. Agricultural machine according to any one of Claims 4-8, wherein the seed metering element (803) is adapted to release the seeds in a release area (SL), and the control unit (451 ) is adapted to control the speed of the seeds transported by the seed metering element (803) so that a first elevated speed occurs at passage through the release area (SL) of a seed retaining means (804) which in the seed transport direction is disposed immediately after the seed retaining means (804) at which trie absence of a seed is determinable.

10. Agricultural machine according to Claim 9. wherein the control unit (451 ) is adapted to control the speed of the seeds transported by the seed metering element (803) so that a second elevated speed, which is lower than the first elevated speed, occurs at passage through the release area (SL) of a seed retaining means (804) which in the seed transport direction is disposed immediately after the seed retaining means (804) which is disposed immediately after the seed retaining means (804) at which the absence of a seed is

11. Agricultural machine according to any one of the preceding Claims, wherein the seed metering element (803) is adapted to rotate around a seed metering axle (805) and to transport the seeds at a distance from the seed metering axle (805), and the control unit (451) is adapted to control the transport speed of the seeds through controlling the rotational velocity of the seed metering element (803).