Seed dispensing mechanisms

A seed dispensing mechanism for a precision row crop planter employs a pressure differential to cause seeds to be held to a series of seed apertures in a rotary disc. The disc is of stainless steel of very thin gauge whereby the disc deforms under the pressure differential to provide a degree of self sealing. The apertures in the disc are formed by chemical etching. A singulator mechanism for removing excess seeds from the apertures comprises singulator members on opposite sides of the row of apertures and presenting a curved profile to the seeds and defining a throat of which the width can be adjusted by a single knob through a high ratio adjustment mechanism.

This invention relates to seed dispensing mechanisms. In particular, but 
not exclusively, the invention relates to such mechanisms for use in 
precision planters in which seeds are selected and dispensed individually 
as opposed to seed dispensing mechanisms in which the rate of dispensing 
is controlled by varying the flow of seed. So-called precision-type 
dispensing mechanisms are used for dispensing seeds in drills and planters 
for such row crops as small bean and vegetable seeds, and natural or 
pelleted sugar beet, as opposed to such cereal seeds as wheat, barley and 
the like which are usually dispensed in a less precise way. 
More particularly, the invention relates to seed dispensing mechanisms 
employing a pressure differential to cause seeds to be held to a series of 
seed apertures in a rotary member such as a plate or disc. Usually, the 
arrangement is such that a vacuum is applied to one side of the disc and 
the seeds are held against the apertures on the other side of the disc by 
the atmospheric air pressure. In use, the disc is rotated, seeds are 
picked up from a seed reservoir by the apertures in the disc, excess seeds 
are singulated and the individual seeds remaining on the disc are then 
dispensed one at a time at a discharge point located on the path of travel 
of the seed apertures after singulation has taken place and before the 
apertures re-enter the reservoir. 
Such vacuum-type seed dispensing mechanisms are comparitively well known 
and have achieved some technical success. However, several problems remain 
to be solved in such mechanisms including in particular problems in 
relation to the disc or plate and the housing with which it co-operates, 
and the mechanism for singulating seeds picked up by the plates. 
Firstly, there is the requirement that the seed apertures formed in the 
disc or plate are reliably filled as the apertures pass through the seed 
reservoir. Occasional misses or blanks result in corresponding gaps in the 
field planted, and this is unacceptable to farmers. Other problems are to 
some extent technically related with these and concern the manufacture of 
the disc or plate in a sufficiently flat or smooth condition and with the 
seed apertures formed-with adequate precision. 
As regards filling of the seed apertures in the disc, one particular 
problem relates to maintenance of the vacuum or pressure differential. 
Obviously, the sealing arrangement between the disc and its housing must 
be effective to allow the maintenance of a steady and adequate vacuum on 
the relevant side of the disc. Irregularities in the sealing arrangement 
will give rise to reduction of the vacuum and interference with the seed 
selection. Localised sealing failures, although perhaps within the 
capacity of the vacuum pump so far as concerns maintenance of the overall 
vacuum, can cause localised variations in the vacuum whereby seed 
selection becomes irregular. 
Previously proposed solutions to this sealing problem have concentrated 
mainly on the provision of a seed selection disc which is precisely flat 
and smooth and seals effectively with the adjacent structure. However, 
this approach has led to the adoption of rather thick, heavy and precisely 
rolled and machined discs and corresponding fine tolerances on the 
associated structure against which they seal. This is an expensive and 
somewhat unsatisfactory approach to the problem and we believe that 
improvements in this respect are needed. 
Moreover, so far as manufacture of the disc is concerned, conventionally 
the seed apertures have been drilled in the heavy disc described above and 
countersinks have been provided for each seed aperture on the vacuum side 
of the disc. 
It will be appreciated that the drilling and countersinking of the discs in 
this manner tends to produce burrs and swarf which obviously must be 
removed before use of the disc. However, in such a cleaning and polishing 
operation there is a tendency for the burrs merely to be pushed back into 
the holes where they then subsequently interfere with seed selection. 
Moreover, the depth of the holes themselves, despite the countersinking, 
itself tends to promote the physical trapping of two or more seeds in each 
aperture. 
A further requirement relates to the need for an efficient singulation 
mechanism to reduce the incidence of doubles or triples i.e. two or three 
seeds, or more provided in each hole in the disc. Previously proposed 
singulating mechanisms are somewhat simple and crude in that the mode of 
adjustment of the singulating action is extremely coarse whereby it is 
difficult to achieve the optimum setting of the mechanism for any given 
set of circumstances. 
Clearly, improvements are needed in respect of the above-discussed aspects 
of the manufacture and construction of seed dispensing mechanisms. 
An aim of the present invention is to provide a seed selection disc and a 
seed dispensing mechanism incorporating same in which at least one of the 
problems identified above is alleviated or overcome. 
According to the invention there is provided a seed selection plate and a 
seed dispensing mechanism as defined in the accompanying claims. 
One aspect of the invention as provided in an embodiment described below 
includes a seed selection plate for a differential pressure seed selection 
mechanism, the plate having spaced seed selection apertures formed 
therein, wherein the plate is flexible to the extent that the plate 
deforms under the pnuematic pressure differential applied thereto so as to 
provide a degree of self sealing with respect to a support therefor. 
Another aspect of the invention as provided in an embodiment described 
below is a seed selection plate for a differential pressure seed selection 
mechanism, the plate having spaced seed selection apertures formed 
therein, wherein the thickness of the plate lies in the range of 0.125 to 
0.625 millimeters. The plate preferably comprises a metallic material such 
as stainless steel. 
A further aspect of the invention as provided in an embodiment described 
below is a seed selection plate for a differential pressure seed selection 
mechanism, the plate having spaced seed selection apertures formed 
therein, wherein the plate is formed with said seed apertures by a 
non-mechanical means such as chemical etching. 
Another aspect of the invention as provided in an embodiment as described 
below is a seed selection plate for a differential pressure seed selection 
mechanism, the plate having spaced seed selection apertures formed 
therein, wherein the seed selection plate comprises stainless steel having 
a thickness between 0.125 millimeters and 0.625 millimeters and a 
flexibility such that the plate deforms under the pneumatic pressure 
differential applied thereto to provide a degree of self sealing, the 
plate having said seed apertures formed therein by non-mechanical means 
such as chemical etching. 
Preferably, the seed selection plate comprises stainless steel of thickness 
between 0.2 and 0.3 millimetres. 
A single row of circumferentially spaced seed apertures may be formed in 
the selection plate. Alternatively, two radially spaced rows or three 
radially spaced rows of such seed apertures may be formed in the plate. 
In a seed dispensing mechanism incorporating the seed selection plate, 
support means for the plate and engagable therewith on the vacuum side 
thereof may be provided. The support means may comprise a 
circumferentially extending rib having a flat upper surface for engagement 
with the plate. The plate may be supported at or in the region of its 
outer periphery on an outer circumferentially extending support member 
formed with a flat surface for engagement with the plate. A further 
cirumferentially extending support member or rib may be provided radially 
inwardly of the outer support member. Corresponding support members may be 
provided between the rows of seed selection apertures. The plate support 
members may be mounted on a housing member having connection means thereto 
whereby said differential pressure may be set up across the plate. 
A central turntable may be provided to support the inner region of the seed 
selection plate. Drive formations are preferably provided on the turntable 
for driving engagement with the plate. 
A blanking member is preferably provided for engagement with the disc to 
blank-off the seed apertures on the vacuum side whereby the seeds may be 
discharged. Seed discharge means is preferably also provided to dislodge 
the seeds. The seed discharge means may provide for an air flow through 
the seed apertures from the vacuum side of the discs to the other side to 
dislodge the seeds. 
A further aspect of the invention as provided in an embodiment described 
below is a seed dispensing mechanism comprising a rotatable seed selection 
member having a row of seed apertures therein to pick up seed from a 
supply, and a seed singulation mechanism to remove excess seed from said 
apertures prior to dispensing seed from the plate, wherein said 
singulation mechanism comprises a pair of singulator members positioned on 
opposite sides of said row of seed apertures and being position-adjustable 
towards and away from each other to adjust the singulation effect. 
The singulator members preferably present a generally smoothly curved 
profile to the seed. For example, the singulator members may be generally 
cylindrical in form and arranged with their axes at right angles to the 
plane of the seed selection plate. The seed singulator members may be 
mounted on oppositely-movable supports. Preferably, a single actuator 
member is provided to effect said position-adjustment of the singulator 
members. 
Preferably also, said singulator members positioned on opposite sides of 
said row of seed apertures are spaced apart along said row so as to act 
successively on seeds passing therebetween. Preferably said actuator 
member for the oppositely movable supports is arranged to act thereon 
through a high ratio drive whereby fine adjustment of the singulator 
members can be provided manually. 
Preferably also, said oppositely-movable supports each carry two or more 
singulator members to co-operate with two or more rows of said seed 
apertures. 
The invention also provides a seed selection plate and a seed dispensing 
mechanism comprising any novel feature or novel combination of features 
disclosed herein.

FIGS. 1 to 8 show a seed dispensing mechanism 10 which forms part of a row 
unit (not shown) of a precision planter (not shown). The planter is of the 
kind comprising a transversly extending toolbar adapted to be mounted on 
the hitch links of an agricultural tractor and having laterally spaced row 
units mounted at intervals along its length, each row unit having its own 
seed hopper, seed dispensing mechanism and coulter assembly and press 
wheel. Seeds from the seed hopper of each row unit are selected one at a 
time by the dispensing mechanism and dropped into a furrow opened by the 
coulter assembly, the furrow is then closed and the soil is pressed down 
by the press wheel. Such planters are used for sowing carrots, onions, 
lettuces and other small vegetable seeds. 
A seed dispensing mechanism 10 has its own seed reservoir and discharges 
selected seeds into a discharge assembly (not shown) very close to the 
soil-opening coulter. The dispensing mechanism 10 is mounted at about 3.8 
centimeters clearance from the ground whereby the seeds are discharged 
very close to the furrow and there is very little loss of accuracy between 
the dispensing mechanism and the soil itself. Moreover, the direction of 
rotation of the seed selection plate (described below) of the dispensing 
mechanism is such that the seed is dispensed with a velocity in the 
opposite direction to the ground speed of the implement whereby the net 
velocity of the seed with respect to the ground is very low. 
Seed dispensing mechanism 10 broadly comprises a housing 12, a seed 
reservoir 14, a drive 16, a seed selection plate 18, a seed singulation 
mechanism 20, and seed ejection means 22. 
Housing 12 is formed as an aluminium casting and comprises a vacuum side 
body member 24 and a seed side body member 26 detachably secured together 
by means of releasable fasteners at 28, 30 and having a connection pipe 
(not shown) on body member 24 whereby a hose is connected thereto from a 
vacuum pump driven by the tractor's p.t.o. (or by a hydraulic drive or 
other power source) and effective to lower the pressure between plate 18 
and body member 24 to about 80 millibars (i.e. 920 millibars below 
atmospheric pressure). Housing 12 could alternatively be formed as a 
plastic moulding e.g. of nylon or the like. 
Seed reservoir 14 is generally wedge-shaped and funnels seed down to the 
seed dispensing mechanism and to seed selection plate 18 in particular and 
is formed integrally with housing 12. Seed selection takes place in a seed 
selection zone 32 through which apertures 34 in selection plate 18 pass, 
to pick-up seeds. 
Drive 16 comprises a pulley 36 driven by a belt (not shown) from a ground 
wheel or press wheel so as to rotate at a speed directly related to the 
ground speed of the planter or drill. The drive rotates seed selection 
plate 18 and associated components described below. 
Seed selection plate 18 is shown in FIG. 3 and is in the form of a circular 
disc formed of grade 301 hard rolled stainless steel sheet of thickness 
0.254 millimeters. The disc is of diameter 207 millimeters and is formed 
with three rows 40, 42, 44 of seed apertures 34 arranged coaxially with 
plate 18 (axis 46) and of diameters 190 and 162 and 134 millimeters 
respectively. 
Each row 40, 42 and 44 of apertures 34 comprises sixty apertures spaced at 
six degree intervals around the circumference of the disc so that the 
apertures on the three rows are arranged in radially aligned groups as 
indicated by reference radius 48. It is to be understood that such an 
arrangement of the apertures is by no means essential. 
The seed apertures 34 are each circular in shape and of diameter 0.5 
millimeters and formed by a non-mechanical process of chemical etching. 
The etching is effected by spraying ferric chloride onto both sides of 
plate 18 after the latter has been appropriately masked by a photographic 
process so that only the desired apertures are etched. It is to be noted 
that the plate 18 is rolled as flat as possible prior to etching. 
A series of six drive apertures 50 are formed in the central region of 
plate 18 to receive six corresponding drive pins 52 projecting axially 
from a turntable 54 driven by pulley 36 and serving to support the central 
region of plate 18. 
Between the outer periphery 56 of turntable 54 and the outer edge 58 of 
plate 18, the latter is supported against the vacuum present in the drive 
side of housing 12 by means of three circumferentially extending ribs 60, 
62 and 64 disposed at radially spaced intervals, extending in circular 
paths, and each having a flat outer surface for sealing engagement with 
plate 18. The three rows of seed apertures 40, 42 and 44 are 
correspondingly spaced between the outer periphery 56 of turntable 54 and 
the ribs 60, 62 and 64, as indicated in FIG. 2. 
Within seed reservoir 14 is provided seed agitator means comprising a shaft 
66 rotated by drive pins 52 through a paddle wheel 68. The shaft carries 
agitator pins 70 to agitate the seed in the seed selection zone 32. Shaft 
66 extends radially of seed selection plate 18 and pins 70 are mounted 
thereon by hubs 71. Drive apertures 50 which receive drive pins 52 are 
located at angular spacings of 60 degrees and thus there is a considerable 
amount of lost motion in the drive to shaft 66 whereby agitating pins 70 
have an irregular circular motion which serves to provide a particularly 
effective agitating action. 
Seed singulation mechanism 20 will be described in detail below and 
comprises adjustable mechanical means to doff or remove excess seeds from 
the rows of apertures 40, 42, 44 and thus leave, as far as possible, a 
single seed in each aperture 34. 
Details of the structure of singulation mechanism 20 are shown in FIGS. 4, 
5 and 6. The main structural components include a manual adjustment knob 
72 actuating a shaft 74 connected to a pair of carriers 76, 78 which are 
slidably mounted on a pair of guide pins 80, 82 and carry singulator 
members 84, 86, 88, 90, 92 and 94. Rotation of knob 72 rotates shaft 74. 
Two threaded portions 96,98 on shaft 74 are of opposite hands and screw 
threadedly engage female threads on carriers 76 and 78 whereby rotation of 
knob 72 about its axis 100 causes movement of carriers 76, 78 in opposite 
directions i.e. towards or away from each other. The pitch of the threaded 
portions 96, 98 is 56 turns per inch, which is a relatively high ratio 
drive whereby the knob offers a means of fine adjustment of the positions 
of the carriers. The latter are slidably mounted on guide pins 80, 82 
which are secured in radially extending positions to housing 12. A coiled 
compression spring 102 acts between a head portion 104 of housing 12 and 
outer carrier 76 to hold the assembly in any selected adjusted position. 
Singulator members 84 to 94 are cylindrical in form and arranged in pairs 
84, 86; 88, 90; and 92, 94. The members of each pair are radially and 
circumferentially offset so that the rows 40, 42 and 44 of apertures 34 
can pass between the members of each pair. Adjustment of knob 72 causes 
the singulator members of each pair to move towards or away from its row 
of seed selection apertures. 
As can be seen in FIG. 4, the singulator members make flat face-to-face 
contact with seed selection plate 18. 
The seed ejection means 22 comprises a vacuum cut off plate 106 against 
which the vacuum side of plate 18 runs, whereby the seeds are no longer 
held by the vacuum. This causes the seeds to fall from the plate by 
gravity. 
In use, seed reservoir 14 is full of seed and drive 16 rotates seed 
selection plate 18 about axis 46 in the clockwise direction as seen in 
FIG. 1. Seed is picked up at seed selection zone 32, excess seeds are 
doffed by singulation mechanism 20 and the seeds are dispensed one-by-one 
at cut off plate 22 straight into the furrow opened by the coulter (not 
shown). The arrangement is such that the seeds from each of the rows 40, 
42, 44 of apertures are delivered to individual furrows in the soil. 
By virtue of the fact that seed selection plate 18 is of thickness only 
0.254 millimeters as compared with the conventional disc thickness of 1.55 
millimeters, it is very much more flexible than a conventional seed 
selection disc and is deformed by the vacuum applied to the vacuum side of 
the disc so as to effect a degree of self-sealing with respect to the 
circular support ribs 60, 62 and 64 and the outer periphery of turntable 
54. Thus, the outer portion of plate 18 together with the turntable and 
the ribs and the vacuum side body member 24 form a substantially airtight 
vacuum chamber from which air is evacuated by the vacuum pump and to 
which, to a first approximation, air can only be admitted through the 
apertures 34. Thus, the vacuum applied to plate 18 is easily maintained, 
is substantially constant around the whole circumference of the apparatus 
and is mainly uneffected by minor irregularities in the housing. 
As regards the seed selection apertures 34 themselves, these are 
particularly smooth and regular with no burrs, swarf or other 
irregularities to interfere with the selection and retention of seeds. The 
apertures are formed chemically whereby each aperture has a smooth rounded 
profile. Moreover, no mechanical action is involved in the formation of 
the apertures and hence no corresponding distortion of the disc occurs. 
Singulation mechanism 20 is adjusted by means of knob 72 to achieve the 
maximum singulation effect. By adjusting the throat defined by the two 
singulation members of each pair, the point can be reached where all the 
excess seeds from a high proportion of the apertures 34 are removed before 
the seeds reach the seed release zone. 
In FIGS. 7 to 12 there are shown a variety of singulator member forms. 
Those of FIGS. 7 and 8 are the same as those of FIG. 6, being generally 
cylindrical in form. In FIGS. 9 and 10 is shown a generally frustoconical 
form of singulator member 108 in which the larger face 110 contacts disc 
18. 
In the embodiments of FIGS. 11 and 12, the singulator members are of thin 
plate-like form and mounted on the carrier members by bonding onto the 
bases of the cylindrical (or other shape) members thereon. These 
plate-like singulator members exert a lifting effect on the seed to 
produce the desired effect. In both cases, the singulator members present 
a curved profile to the seed and define an adjustable throat through which 
the rows of seed apertures pass. 
Many modifications can be made in the above-described embodiments without 
departing from the scope of the invention, including variation of the 
size, thickness and material of the seed selection plate 18. For example, 
the diameter of the plate is chosen to suit the size of the dispensing 
apparatus. One, two, three or more rows of seed apertures can be provided 
in it. The spacing of the rows and the spacing of the apertures in each 
row can be varied according to the seed requirements. The apertures need 
not be radially aligned. The size of each aperture can likewise be varied 
to suit the seed. 
As regards the material of the disc, stainless steel is preferred in that 
it has good corrosion resistance and static electricity effects are 
avoided. However, with the advent of new materials, it may be possible to 
provide a relatively flexible disc which does not suffer from electro 
static problems and which is not entirely formed of metallic material. 
The range of thickness of the disc, measured between its opposite sides, so 
far as metals such as stainless steel are concerned is from 0.125 to 0.625 
millimeters with the range of 0.2 to 0.3 millimeters being preferred. 
It may be desired to provide means to reduce friction and wear between the 
plate and its supports, such as a layer of polytetrafluoroethylene or 
graphite or carbon or other lubricating materials. 
The invention may also be adapted for use with seed selection mechanisms 
whereby the pressure differential is generated by raising the pressure on 
the seed side of the disc to above atmospheric pressure. 
In the singulation mechanism, more than one singulator or member may be 
provided on each side of each row and other shapes of singulator member 
may be adopted. 
Furthermore, it is to be understood that of course on a theoretical basis 
any degree of vacuum will cause a corresponding degree of deflection of a 
seed selection plate if applied thereto. Such deformation is not normally 
enough to improve the sealing of the disc at all. 
Other methods of non-mechanical generation of the seed apertures may be 
provided, and the invention provides a method of making a seed selection 
plate by such methods. 
By the term "singulation" as used in this specification it is to be 
understood that the term does not necessarily refer to the production of 
the optimum situation where only one seed remains in each seed selection 
aperture. This result depends very much on the careful adjustment of the 
mechanism. Accordingly, the term "singulation" is intended to refer to the 
reduction in the number of "doubles" and "triples" in the seed apertures. 
Moreover, for this purpose, the embodiments of FIGS. 11 and 12 have been 
tested with plate thicknesses from 10 to 30 thousands of an inch (0.254 
millimeters to 0.762 millimeters).