SEED DISPENSING MECHANISMS

Abstract: A seed selection arrangement for a differential pressure seed selection mechanism comprises a seed selection plate assembly (144) and a flexible seal (14) for defining regions of differing pneumatic pressures. The seed selection plate assembly comprises an apertured flexible seed selection plate (144) mountable on a rotatable support plate (118). The support plate (118) is substantially thicker than the seed selection plate (144). In another aspect of the invention there is provided a seed dispensing mechanism having control means for controlling the application of the pressure differential for seed discharge purposes. The control means is in the form of a resiliently loaded control member mountable for sliding engagement with the seed selection plate assembly.

Description: SEED DISPENSING MECHANISMS This invention relates to a method and apparatus for dispensing seed. More particularly, the invention relates to a method and apparatus in which a difference in pneumatic pressure is employed for seed selection purposes. In the case of known pneumatic seed selection mechanisms as used in currently available farm machinery, and indeed in such mechanism as have been available commercially over the last 30 years or thereabouts, the arrangement is generally as follows. A stainless steel seed selection disc is arranged to co-operate with a body member or vacuum manifold, generally of a plastics material, the disc being rotatable and the body member being fixed. The disc and the body member are in sliding face-to-face contact over a substantial proportion of the side surface of the disc. Sub-atmospheric pressure is applied to the disc over a generally arcuate sub-area of the disc in which seed selection apertures are formed on a pitch circle centred on the rotation axis of the disc. Thus, a sub-atmospheric pressure or "vacuum" applied to the disc over the arcuate area effects seed selection from a seed supply housed in the body member and holds the selected seeds to the disc as the disc rotates. In accordance with well- established practices, the excess seeds are doffed from the seed selection apertures as the disc rotates, until only one seed remains. Then, the vacuum is blanked-off in order to dispense the seeds selectively from the apertures. All the above technology is extremely well-known and has been widely used internationally over the last 30 years at least, and so far as commercial use is concerned, has been used more or less exclusively in the form described. Shortcomings of this prior system which have equally been well-known over this long period relate, inter alia, to the wearing characteristics of the mechanism and the consequential need for replacement parts. As would be expected by those aware of the characteristics of the working environment of such mechanisms, and indeed of the stainless steel and plastics materials themselves, wear occurs both in relation to the body member and the stainless steel disc itself. One reason for this is the fact that the mechanism in use acts as a vacuum cleaner tending to attract significant amounts of dust in what is inevitably a very dusty situation when seeds are being planted in anything other than damp conditions. Accordingly, we have identified a significant need for improvements in relation to methods and apparatus for pneumatically selecting seed wherein the wearing characteristics of the method and apparatus are improved. Accordingly in certain embodiments of the invention there is provided a method and apparatus for dispensing seeds wherein seeds are selected employing a difference in pneumatic pressure applied to a seed selection disc or plate having seed selection apertures. In these embodiments of the invention, the arrangement is such that the seed selection disc or plate assembly is itself capable of supporting the load arising from the difference in pneumatic pressure applied to it and a flexible seal co-operates with the disc or plate to define regions of differing pneumatic pressure. By arranging for the disc or plate to be self- supporting in combination with flexible sealing means, the advantage is provided that the seal represents the only significant surface making rubbing contact with the disc or plate, and wear between these surfaces is accordingly correspondingly minimised. For example, when a lip-type seal is employed, the seal makes contact with the disc or plate only over the very narrow lip area, for example substantially line contact in an annular shape, and therefore it is only along this annular line where wear can occur. Because the disc or plate is self-supporting, it does not need to bear or rub against any other structure for reasons of support. In an embodiment of the invention, the advantage is provided that substantially all or a major proportion of the frictional face-to-face rubbing contact between the rotating disc or plate and the non-rotatable body of prior art mechanisms is eliminated. In the embodiment, the seed selection disc is accordingly no longer a sacrificial component of the mechanism. The thickness of the seed selection disc or plate and its mode of mounting are such that it is self-supporting and thus it differs significantly in these respects from the discs or plates of prior art mechanisms which have not needed to perform this function since they have been supported by the associated non-rotatable body structure. One more specific aspect of the invention relates to the means for selecting and dispensing relatively small seeds such as carrot or lettuce or tomato seeds - as opposed to maize or field beans or the like seeds. Pneumatic seed selection mechanisms applicable to small seeds such as lettuce seeds have hitherto been subject to difficulties arising from the fact that the small seeds apertures need to be so very small, as compared with the apertures applicable to, for example, field beans. As a practical matter, it is difficult and expensive to make seed selection apertures through the metallic structure of a seed selection disc and which are small enough to be suitable for small seeds such as lettuce. Typically, such an aperture might have a diameter in the range of 0.5 to 0.8 mm. In addition to the mere production cost and difficulty of providing holes at such a size without any burrs or other irregularities, there is the attendant problem of dust and dirt and debris lodging in such holes during use. Conventionally, seed holes are provided in relatively thick discs and the provision of an aperture at such a diameter through a conventional disc means that the aperture is effectively (as compared with its diameter) a tube in which debris can be relatively easily lodged. Moreover, the pneumatic seed selection mechanism applies vacuum to the disc and foreign matter and debris is constantly drawn into these tubes and they tend to become blocked. The conventional solution to this problem is to countersink the aperture from the non seed-selection side of the disc. However, this arrangement is not particularly satisfactory since it requires relatively complicated additional manufacturing procedures. Also, the arrangements for sealing such discs have hitherto suffered from the same disadvantages as are discussed elsewhere in the specification. Accordingly, there is a need to provide a seed selection disc or plate arrangement, particularly for use in relation to a pneumatic seed selection mechanism of the kind disclosed above, but applicable more widely also, in which the hitherto conventional countersink arrangement is replaced by an alternative arrangement which retains the advantages of the countersink arrangement in terms of the seed selection hole proportions, as they affect the resistance of the seed selection apertures to become plugged or otherwise to suffer from technical disadvantages in use, while offering improvements in relation to other aspects of this construction, including manufacturing. There is disclosed in our own European patent EP 0 145 237- a pneumatic seed selection mechanism in which a thin and flexible or floppy disc is employed. We incorporate herein by reference the entire text and drawings of this prior publication by way of additional disclosure. This enables the convenient and relatively inexpensive production of seed selection apertures for small seeds. This can be done, for example, by a simple etching technique. More than one row of such apertures can be employed. The seed selection disc runs against a plastics manifold or gallery member to define the regions in which vacuum is applied to the disc. The disc can be likewise provided with larger seed selection apertures so as to enable the dispensing of larger seeds such as field beans. To the best of our knowledge, this prior-patented thin disc system represents the only way in which the entire range of seed sizes from large seeds to small seeds can be effectively dispensed by a single metering mechanism using interchangeable discs and a vacuum selection technique. A shortcoming however of our above-identified and prior patented thin disc pneumatic seed selection mechanism arises in dusty conditions in which dust finds its way between the rotating thin disc and the non-rotating plastics manifold and eventually causes some wear of the thin disc. In non dusty conditions, such a disc lasts the lifetime of the planter. However, some improvement in this respect is desirable and according to this aspect of the present invention there is provided a method and apparatus as defined in claim 1 of the accompanying claims. In the embodiments of this aspect of the invention there is provided a seed selection mechanism and a seed selection plate or disc assembly comprising a relatively thin flexible seed selection disc or plate. The term "flexible" as used in this specification in relation to a disc or plate is intended to mean that the disc or plate is flexible to the extent that it is able to deform under the pneumatic pressure differential applied thereto so as to provide a self sealing effect with respect to its support. In an embodiment, a seed selection plate or disc has a thickness of betweeen 0.20 and 0.30 mm, and the reduced pressure applied to the seed selection plate or disc assembly is in the range of 30 to 100 millibars. In the embodiments, the flexible disc is mounted in relation to a supporting disc or plate. The supporting disc or plate supports the flexible disc against the effect of the applied vacuum. A seal co¬ operates with the supporting disc or plate to define the region in which vacuum is applied to the disc assembly. By providing an arrangement in which a flexible disc mounted on or in relation to a supporting disc or plate, is able as an assembly to co-operate with a seal, for example a lip-type seal, the advantage is provided that the seal produces negligible wear of the supporting disc or plate, even under dusty conditions, because it is loaded against the disc or plate only to the extent normal for a seal of that particular kind. Thus, in the case of a lip-type seal, the loading is that which is produced by the relevant degree of deflection of the lip of the seal itself. Because in the embodiment the lip or other type of seal contacts the seed selection disc assembly only on the supporting disc or plate itself, there is no contact at all between the seal and the flexible disc, and therefore no wear at all of the latter at the region of sliding and sealing contact. In use, the vacuum applied to the assembly draws the flexible disc against its support and they function in this respect as one structure. The flexibility of the disc allows it to accommodate itself to any slight irregularities in the linearity of the support disc or plate under the action of vacuum applied to both. In the embodiment, a circular and conventional proprietary lip-type seal may be employed. The diameter of this seal is arranged to fully encompass the seed selection region defined by the row or rows of seed selection apertures in the flexible disc so that vacuum is applied to the entire row within the seal, and the row of seed selection apertures does not cross the seal and cause wear, as in the case of the Deere prior proposal mentioned below. Generally, the arrangement will be such that the disposition of the seal relative to the seed selection disc and its support plate or disc is such that vacuum is applied to the entire inner region of the double disc or plate assembly, apart from the region in which the vacuum is removed by means of the vacuum cut-off assembly in which a control member covers over a portion of the disc assembly and atmospheric pressure may be applied to the seed selection holes. In accordance with this aspect of the present invention, a seed selection disc or plate assembly for use in a pneumatic seed selection mechanism comprises primary and secondary rotatable apertured plates or discs. For the purpose of dispensing small seeds, the primary dispensing plate is formed with at least one row of appropriately sized apertures. One or more corresponding apertures or openings are formed in the secondary plate. The apertures in the secondary plate are substantially larger than those in the primary plate and are disposed so as to, at least partially, overlap with those in the primary plate. The arrangement may be such that the apertures in the secondary plate are generally aligned with those in the primary plate and fully encompass at least some of these. The material of the primary plate is of substantially reduced thickness as compared with that of the secondary plate. As a result, the proportions of the small and large size apertures in the primary and secondary plates are such as to tend to inhibit blocking of the latter by foreign matter. The co¬ operating arrangement with the secondary disc provides support for the primary disc and allows the application of vacuum to the assembly. Indeed, both discs are held together by the vacuum applied to the assembly. Accordingly, it can be seen that in the embodiment the advantages of the countersink arrangement are combined with those of the self- supporting disc while permitting the dispensing of small seeds with the required ability to resist the tendency for the apertures to become blocked. The application of vacuum to the seed selection apertures in the primary flexible disc from the vacuum chamber through the secondary supporting disc or plate in the embodiments is by means of said apertures or openings formed in the supporting disc or plate. In one embodiment there is provided an aperture or opening in the supporting disc or plate for each of the seed selection apertures in the flexible disc. Thus in one embodiment, the supporting disc is itself in the form of a seed selection disc for large seeds (with its projecting seed-stirring elements removed) . Alternatively, the supporting plate or disc can be provided with elongated openings communicating with the small seed selection apertures in the flexible disc. In some cases it may be convenient to provide the supporting disc or plate merely with an annular opening at the appropriate location with occasional (three or more) transverse lands linking its outer portion to its inner portion. Generally, the same supporting disc or plate will be used for each one of a range of flexible discs having differing seed selection hole sizes, but it may be desirable for particular cases to provide a supporting disc or plate for particular ones of such a range. A further aspect of this invention relates to the provision of a pneumatic seed selection mechanism in which an improved arrangement is provided for the controlled application of "vacuum" (meaning a pressure lower than atmospheric pressure) to the seed selection disc or assembly. There is disclosed in, inter alia EP-A-0 141 637 (Deere) a pneumatic seed selection mechanism in which a seal having a non-circular shape serves to define and separate regions in which vacuum is applied to the seed selection disc and in which vacuum is not thus- applied. Shortcomings of this prior proposal include the cost of the seal, which is a non-proprietary item, the fact that the seed selection holes consistently cross the seal during use and thus wear it, and the fact that the vacuum cut-off region is fixed and determined by the seal shape and cannot be changed as, for example, is required in order to change the characteristics of the mechanism for particular crops. US-A-5 401 035 (Schoenmaekers) discloses a seed selection mechanism in which an O-ring is employed. There is no disclosure of the system for controlling the application of vacuum in the region where seeds are to be removed from the disc. It must be expected that the mechanism employs a gallery system as indeed is common in planters in commercial use in which the control of the application of vacuum is achieved by the use of galleries moulded into a manifold or gallery member against which the seed selection disc runs. Such an arrangement is likewise subject to the shortcoming that the arrangement for control of the application of the vacuum to the disc cannot be readily varied for different crops since this would require replacement or interchange of the gallery member structure. According to this aspect of the invention there is provided a seed dispensing mechanism as defined in claim 13 of the accompanying claims. In the embodiment, since substantially the entire centre region of the seed selection disc has vacuum applied to it, effectively as many lines of seed can be selected by means of seed selection apertures arranged in concentric circles, as may be desired. Normally there will be from one to three lines of seed selected. The sealing member is preferably of standard circular shape and vacuum is applied to the entire surface of the disc within this circular region defining an inner seed selection region. Control of the application of vacuum is achieved by means of a resiliently-loaded control member which slidingly engages the disc (where a self-supporting disc is used) or the disc assembly (where the combination of a self-supporting disc and a flexible or floppy disc are employed) so as to reduce or eliminate the effect of the vacuum applied to the rearface of the disc or the disc assembly. The control member may be provided in the form of a spring-loaded plastic pad. This pad is able to accommodate the small degree of movement of the self- supporting disc under the action of the vacuum applied to it, and/or accommodate any irregularities in the linearity of the surface of the disc. In an embodiment, the control member may be of a circumferential length (with respect to the disc) such as to cover a series of seed selection apertures in the disc or disc assembly, whereby, although the individual seeds are removed from the disc as soon as the vacuum is cut off from the seed selection holes, nevertheless the then open holes do not immediately have vacuum reapplied to them, with the attendant possibility of directly attracting foreign matter or debris before the vacant holes pass through the seed reservoir region and pick up further seeds. A further feature of the control member in the embodiments is the provision of an opening or channel through to the atmosphere at a region in the control member, which region is aligned with the row of seed holes. In the case of a control member or control members covering more than one row of seed holes, it would be arranged that this opening provides access to atmosphere to both or each row of seed apertures. In this way, the removal of the vacuum applied to the seed selection disc by the presence of the control member is further enhanced by positively allowing the pressure within each seed selection aperture in turn to be brought back to atmospheric pressure. Such an arrangement is preferable to the previously proposed technique of providing a blower delivering a jet of air onto the disc in the relevant region so as to blow seed off. Such an arrangement tends to interfere with the controlled deposition of seed at well defined locations. Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which :- Fig 1 shows a cross section through a seed selection mechanism; Figs 2 and 2A show a cross section through a seed selection mechanism similar to that of Fig 1 showing a modification for small seeds, Fig 2 being an exploded view; Fig 3 shows an axial view of the seed selection mechanism of Fig 1 as seen in the direction of arrow III therein; and. Fig 4 shows a partial inverted section on IV - IV of Fig 3 illustrating seed discharge details. In Figs 1 and 3, the general construction and mode of operation is generally as described above. The principal constructional items of the seed dispensing mechanism 10 comprise a non-rotatable body or housing 12 carrying an annular non-rotatable seal 14 having a flexible lip 16 which co-operates with a self-supporting seed selection disc 18 mounted on a bearing 20 for rotation about an axis 22 and provided with rows of seeds selection apertures on pitch circles indicated at 24, 26 and 28. Disc 18 is sufficiently stiff to support itself against the vacuum applied to it by a vacuum pump connected to housing 12 and tending to bend the disc, especially in its outer regions, in the left-to-right direction in Fig 1. Flexible lip 16 accommodates this movement. In Fig 3 item 30 indicates a seed supply zone fed by seeds from a hopper (not shown) and through which the seed selection apertures on the pitch circle 24 passes. Item 32 indicates a seed singulating mechanism of generally known construction and adjustable in an arc between positions indicated at 34 and 36 to vary the singulating effect. Item 38, shown in more detail in Fig 4, shows the resiliently-loaded control member for controlling the removal of vacuum to an area of disc 18 for seed discharge purposes. The control member 38 comprises pad 44 which is spring-pressed against disc 18 by spring 46. The spring-loaded pad 44 is able to accommodate any small degree of movement of the self support disc 18 under the action of the vacuum applied to it, as well as accommodating any minor imperfections in the surface of the disc. The control member 38 is provided with a channel or drilling or bore 48 through to atmospheric pressure, the channel 48 being aligned with a seed selection aperture in disc 18. In this way, in use, the removal of vacuum applied to the seed selection disc 18 by the presence of control member 38 is enhanced by positively allowing the pressure within the seed selection aperture at 24 to be brought back to atmospheric pressure. This embodiment has the advantage that the sealing lip does not cross the line of seed selection apertures and therefore has excellent wear characteristics. As can be seen in Fig 3, pad 44 is so shaped as to cover a series of seed selection apertures in disc 18. Although the individual seeds are removed from the disc 18 as soon as the vacuum is cut off from the apertures, by being covered by pad 44, the open apertures do not immediately have vacuum re-applied to them, which would tend to attract foreign matter before the vacant aperture has passed through the seed reservoir to pick up a further seed. In use, seeds are picked up by seed selection apertures 40 froπ seed supply 30 and the seeds are singulated at 32 and finally discharged by the cut-off plate 38. Figs 2 and 2A illustrate one aspect of the invention, relating to the selection and dispensing of relatively small seeds, such as carrot seeds, lettuce seeds, or tomato seeds. The apparatus of Figs 2 and 2A is similar to the apparatus of Fig 1, and like parts have been given the same reference numerals. This apparatus comprises a support disc 118, similar to the seeds selection disc 18 of Fig 1, but with its projecting seed-stirring elements removed. Typically, the disc 118 has a diameter of 2SS millimetres and a thickness of 2 millimetres. The support disc 118 is provided with a row of aperture on the pitch circle indicated at 124. Typically the apertures have a dimension of 5.0 millimetres. As with the arrangement of Fig 1, support disc 118 cooperates with an annular non-rotatable seal 14 having a lip 16 to define the region in which vacuum is applied to the support disc 118. Mounted on the support disc 118 is a flexible seed selection disc 144. The seed selection disc 144 is apertured, with the apertures arranged to align or overlap with the apertures of the support disc IIS. The seed selection disc 144 is of substantially reduced thickness aε compared with the support disc 118 (typically the disc 144 has a thickness of 0.25 millimetres) . The size of the apertures in the seed selection disc 144 are selected according to the type of snail seeds to be dispensed. Typically such apertures night have a dianeter in the range of 0.5 to 2.0 rill metres . In use, support disc 118 is sufficiently stiff to support itself, and the seed selection disc 114, against the vacuum applied to it, with any bending being accommodated by the flexible lip 16 of seal 14. The applied vacuum also serves to draw to, and hold, the seed selection disc 144 against the support disc 118, through the apertures in the support disc 118 forming, in effect, a unitary seed selection assembly. The flexibility of the seed selection disc 144 accommodates itself to any slight irregularities in the linearity of the support disc 118. Therefore, rotation of the seed selection assembly against the seal 14 produces negligible wear of the support disc 118, and because there is no contact between the seal 14 and the flexible seed selection disc 144, no wear occurs in the region of sliding and sealing contact. Furthermore, the relative arrangements of the apertures in the disc assembly provide the advantage of prior art countersink arrangements of resisting the tendency for the apertures to become blocked by foreign matter, but without the attendant difficulties and cost of manufacture.

Claims: CLAIMS : - 1 A seed selection arrangement for a differential pressure seed selection mechanism comprising :- a seed selection plate or disc assembly and flexible sealing means for defining regions of differing pneumatic pressures; characterised in that said seed selection plate or disc assembly comprises an apertured flexible seed selection disc .or plate mountable on, or in relation to, a rotatable support disc or plate. 2 A seed selection arrangement for a differential pressure seed selection mechanism comprising :- a seed selection plate or disc assembly and flexible sealing means for defining regions of differing pneumatic pressures; characterised in that said seed selection plate or disc assembly comprises a relatively thin primary plate and a relatively thick secondary plate; said primary plate being formed with at least one row of relatively small apertures and said secondary plate being formed with substantially larger apertures disposed so as to be able to at least partially overlap the apertures of the primary plate. 3 A seed selection arrangement according to claim 2 wherein apertures in the secondary plate are arranged to be generally aligned with the apertures in the primary plate. 4 A seed selection arrangement according to any one of the preceding claims wherein said flexible sealing means comprises a lip type seal. 5 A seed selection arrangement according to any one 5 A seed selection arrangement according to any one of the preceding claims wherein the flexible sealing means is disposed relative to the seed selection plate or disc assembly to apply, in use, a reduced pressure to the entire inner region of the disc assembly. 6 A seed selection arrangement according to any one of the preceding claims wherein said seed selection plate or disc has a thickness measured between its opposite faces from 0.2 millimetres to 0.3 millimetres. 7 A seed selection arrangement according to any one of the preceding claims wherein said seed selection plate or disc is provided with circular apertures of diameter between 0.5 millimetres and 5.0 millimetres. 8 A seed selection arrangement according to any one of the preceding claims wherein said pressure differential is applied to the face of said support plate remote from said seed selection plate, and a resiliently- loaded control member is engageable with the support plate to reduce or eliminate the effect of the pressure differential, for seed discharge purposes. 9 A seed selection arrangement for a differential pressure seed selection mechanism comprising a rotatable seed selection plate or disc assembly and flexible sealing means for defining regions of differing pneumatic pressure characterised in that said flexible sealing means comprising a lip type seal. 10 A seed dispensing mechanism for an agricultural precision drill or planter, the seed dispensing mechanism comprising :- a housing; a seed supply in the housing; a seed outlet formed in the housing at a location spaced from said seed supply; a rotatable seed selection arrangement having a plurality of circumferentially spaced seed selection apertures formed therein and positioned to pass through said seed supply as the arrangement rotates and thereby to be exposed to the seeds in said supply on one side of the arrangement; a source of pressure differential to be applied to the seed selection arrangement to cause seeds from said supply to be selected therefrom and held in said seed selection apertures as the arrangement rotates; said pressure differential being a vacuum applied to said other side of said arrangement and being sufficient to permit effective seed selection and seed release by said arrangement; and seed release means to release seeds from said seed selection arrangement into said seed outlet whereby, in use, seeds are selected from said supply in said seed apertures and are transported by rotation of said arrangement and released into said seed outlet; characterised by a seed selection arrangement according to any one of the preceding claims. 11 A seed dispensing mechanism comprising a rotatable self-supporting seed selection plate or disc assembly; a source of pressure differential to be applied to one side of the seed selection plate or disc assembly; a non-rotatable flexible seal for defining regions of differing pneumatic pressure across the one side of the seed selection plate or disc assembly; and control means for controlling the application of the pressure differential for seed discharge purposes; characterised in that said control means comprises a resiliently loaded control member mounted for sliding engagement with said seed selection plate or disc assembly. 12 A seed dispensing mechanism according to claim 11 wherein said control member is adapted to cover simultaneously more than one seed selection aperture in the seed selection plate or disc assembly. 13 The seeds dispensing mechanism according to claim 11 or 12 wherein the control member is provided with an opening or channel through to atmospheric pressure which is adapted to be aligned with a row of seed selection apertures. AMENDED CLAIMS [received by the International Bureau on 3 January 1996 (03.01.96) original claims 1-13 replaced by amended claims 1-15 (5 pages)] 1 A seed selection arrangement for a differential pressure seed selection mechanism comprising :- 5 a) a seed selection plate or disc assembly and sealing means for defining regions of differing pneumatic pressures; and b) said seed selection plate or disc assembly comprises an apertured flexible seed selection disc or 10 plate mountable on, or in relation to, a rotatable support disc or plate; characterised in that c) said sealing means for defining regions of differing pneumatic pressures being flexible so as to 15 be adapted to accommodate relative axial movement between the sealing means and said plate or disc assembly during use; and d) said apertured flexible seed selection disc or plate being sufficiently flexible to be able to 20 accommodate itself to irregularities in the linearity of said support disc or plate. 2 A seed selection arrangement for a differential pressure seed selection mechanism comprising :- 25 a) a seed selection plate or disc assembly and flexible sealing means for defining regions of differing pneumatic pressures; b) said seed selection plate or disc assembly comprising a relatively thin primary plate and a 30 relatively thick secondary plate; and c) said primary plate being formed with at least one row of relatively small apertures; characterised in that d) said secondary plate is formed with substantially larger apertures disposed so as to be able to at least partially overlap the apertures of the primary plate. 3 A seed selection arrangement according to claim 2 wherein said apertures in the secondary plate are arranged to be generally aligned with the apertures in the primary plate. 4 A seed selection arrangement according to any one of the preceding claims wherein said flexible sealing means comprises a lip type seal. 5 A seed selection arrangement according to any one of the preceding claims characterised by said relatively thin or flexible seed selection disc or plate lying, in use, totally within the external profile of said relatively thick secondary support disc or plate. 6 A seed selection arrangement according to any one of the preceding claims wherein the flexible sealing means is disposed relative to the seed selection plate or disc assembly to apply, in use, a reduced pressure to the entire inner region of the disc assembly. 7 A seed selection arrangement according to any one of claims 1 to 6 characterised by said sealing means being positioned for sealing engagement with said secondary support disc or plate. 8 A seed selection arrangement according to any one of the preceding claims wherein said seed selection plate or disc has a thickness measured between its opposite faces from 0.2 millimetres to 0.3 millimetres. 9 A seed selection arrangement according to any one of the preceding claims wherein said seed selection plate or disc is provided with circular apertures of diameter between 0.5 millimetres and 5.0 millimetres. 10 A seed selection arrangement according to any one of the preceding claims wherein said pressure differential is applied to the face of said support plate remote from said seed selection plate, and a resiliently-loaded control member is engageable with the support plate to reduce or eliminate the effect of the pressure differential, for seed discharge purposes. 11 A seed selection arrangement for a differential pressure seed selection mechanism comprising a rotatable seed selection plate or disc assembly and flexible sealing means for defining regions of differing pneumatic pressure characterised in that said flexible sealing means comprises a lip type seal. 12 A seed dispensing mechanism for an agricultural precision drill or planter, the seed dispensing mechanism comprising :- a housing; a seed supply in the housing; a seed outlet formed in the housing at a location spaced from said seed supply; a rotatable seed selection arrangement having a plurality of circumferentially spaced seed selection apertures formed therein and positioned to pass through said seed supply as the arrangement rotates and thereby to be exposed to the seeds in said supply on one side of the arrangement; a source of pressure differential to be applied to the seed selection arrangement to cause seeds from said supply to be selected therefrom and held in said seed selection apertures as the arrangement rotates; said pressure differential being a vacuum applied to said other side of said arrangement and being sufficient to permit effective seed selection and seed release by said arrangement; and seed release means to release seeds from said seed selection arrangement into said seed outlet whereby, in use, seeds are selected from said supply in said seed apertures and are transported by rotation of said arrangement and released into said seed outlet; characterised by a seed selection arrangement according to any one of the preceding claims. 13 A seed dispensing mechanism comprising a rotatable self-supporting seed selection plate or disc assembly; a source of pressure differential to be applied to one side of the seed selection plate or disc assembly; a non-rotatable flexible seal for defining regions of differing pneumatic pressure across the one side of the seed selection plate or disc assembly; and control means for controlling the application of the pressure differential for seed discharge purposes; characterised in that said control means comprises a resiliently loaded control pad mounted for sliding engagement with said seed selection plate or disc assembly, and adapted to remove said pressure differential from said plate or disc over the area of said plate or disc. 14 A seed dispensing mechanism according to claim 13 wherein said pad is adapted to cover simultaneously more than one seed selection aperture in the seed selection plate or disc assembly. 15 The seeds dispensing mechanism according to claim 13 or 14 wherein said pad is provided with an opening or channel through to atmospheric pressure which is adapted to be aligned with a row of seed selection apertures. STATEMENT UNDER ARTICLE 19 1 New claims 1 to 15 are filed. 2 Claims 5 and 7 are new, based on matters clearly disclosed in the description and drawings. Claims 6 and 8 to 15 correspond to previous claims 5 and 6 to 13 accordingly. 3 Claims 1 and 13 have been amended to clarify the distinctions from the disclosure in US 4,718,574. 4 Claim 2 has been amended so as to correctly delimit it in two- part form with respect to the disclosure in the US '574 specification. 5 The remaining claims have been amended accordingly editorially.

Inventors: WILLIS ROBERT ANTHONY, WILLIS, ROBERT, ANTHONY
Applicants: WEBB STANHAY LTD, WILLIS ROBERT ANTHONY, STANHAY WEBB LIMITED, WILLIS, ROBERT, ANTHONY
Application year: 1995
Main classification: A01C7
IPC codes: A01C7