Needles for piercing powder capsules

Abstract

A needle (12, 14, Fig 1) for piercing a capsule (2, Fig 1) of powder, for example in a medical inhaler, comprises a first stage, a second stage and third stage. The first stage 18, (48, Fig 5a) is a s

Description

DESCRIPTION Field of the invention The invention relates to the release of powder that is supplied in a sealed capsule. The capsule is pierced by a hollow inlet needle and a hollow outlet needle, then a stream of air is induced to flow sequentially through the inlet needle, the capsule and the outlet needle. The airstream entrains the powder from the capsule for delivery to a desired location. In a typical application, the powder is a medical preparation supplied in capsules and the needles form part of an inhaler device. However, the invention is not limited to medical uses: it could find application in any situation where it is desired to introduce a defined quantity of a powdered substance into a stream of air or other gases. Background of the invention There are different routes for administering medications to the human body, including by inhalation into the oral or nasal cavity. Medications are typically administered in these ways for treating topical and / or systemic conditions, including brain and respiratory diseases. Moreover, the nasal cavity could also be useful for mucosal vaccination against infectious diseases. Medications may also enter the bloodstream via membranes in the nasal cavity for the treatment of a range of other conditions, or directly target the olfactory region for more direct nose to brain delivery. Inhalers are well known medical devices for delivering medications in this way. They may be designed for application to the user’s nose or mouth. The medical preparation may be supplied in powder form or may be a liquid that is converted into an aerosol when the inhaler is operated. In some devices, the flow of air needed to entrain the medication is generated purely by the user inhaling strongly. Other devices include a supply of pre-pressurized air or a pump for generating the required airflow. Some inhalers are disposable in the sense that they are supplied containing one or more 11 06 24 capsules and, when those capsules have been emptied, the device cannot be re-used. In other inhalers, after a capsule has been emptied, it can be replaced with a full one and the device can be reset to its initial condition to be used again. The present invention relates only to delivering substances in powdered form. In other respects, it is 5 applicable to all the alternative types of inhaler described above. For simplicity, the invention will be further described in the context of a medical inhaler but, as previously noted, it can also be used for introducing a powder into an airstream in non-medical contexts. 10 Medical capsules typically comprise a hollow cylindrical body closed by hemispherical or domed ends. They conform to one of a limited number of defined formats, therefore an inhaler can be defined to accommodate a capsule of known shape and dimensions. Capsules are supplied containing a defined quantity of the powdered substance and it is important that a high proportion of the substance should be entrained reliably into the 15 airstream to ensure that the patient receives the intended dose of medication. In known devices, the hollow needles used to pierce the capsule may have a form like a hypodermic needle, comprising a hollow cylinder with one end that is bevelled to create a sharp tip adjacent to the opening. A problem has been identified in that, when 20 one of the hollow needles is inserted into the end of a capsule, it can cause displaced segments of the capsule wall to curl up and create cavities, in which powder lodges and resists entrainment. A further problem is that, if the device is used with the capsule in a generally vertical orientation, powder can collect in the bottom of the capsule around the base of the lower needle and may not be correctly entrained in the airstream. A 25 further problem has been identified that the piercing process can sometime cause tears or splits to propagate in the capsule, creating an aperture in the capsule larger than the needle allowing air and powder to pass out of the capsule around the outside of the needle rather than through it. 30 Summary of the invention The invention provides a needle for piercing a capsule of powder, wherein the needle comprises a first stage, a second stage and third stage; the first stage is a solid cone that 11 06 24 forms a pointed tip of the needle; the second stage comprises a hollow interior and is traversed by apertures that provide an air path between the interior and an exterior of the needle; and the third stage comprises a hollow interior that provides an air path between the interior of the second stage and a base of the needle. The first stage has a first cone angle; the second stage is generally frustoconical and has a second cone angle greater than the first cone angle; and the third stage is generally cylindrical or is generally frustoconical having a third cone angle less than the second cone angle. The third stage may also be traversed by apertures to provide an air path between the interior of the third stage and the exterior of the needle. In some embodiments of the invention, the second and third stages of the needle comprise a cage structure formed by a plurality of ribs that each extend from the first stage to the base of the needle, the apertures being defined by gaps between adjacent ribs. Needles according to the invention may form part of a powder dispenser in which the capsule can be supported. In particular, such a powder dispenser may comprise: a first part comprising a hollow inlet needle; a second part comprising a hollow outlet needle, the inlet and outlet needles opposing one another along an axis; and means for supporting a powder capsule on the axis between the inlet and outlet needles; the first and second parts being movable towards one another to cause the inlet and outlet needles to pierce the capsule. The outlet needle may be a needle according to the present invention. The invention further provides a method of piercing a powder capsule in a powder dispenser, the method comprising the steps of: supporting the powder capsule on an axis between a first part comprising a hollow inlet needle and a second part comprising a hollow outlet needle, the inlet and outlet needles opposing one another along the axis; and moving the first and second parts towards one another to cause the inlet and outlet needles to pierce the capsule; wherein, as the first and second parts move towards one another: a first stage of the outlet needle forms an initial opening in a wall of the capsule, the first stage comprising a solid cone that has a first cone angle and forms a tip of the needle, a second stage of the outlet needle rolls segments of the capsule wall away from 11 06 24 the initial opening, the second stage comprising a hollow, generally frustoconical body that has a second cone angle greater than the first cone angle; and a third stage of the outlet needle radially compresses the rolled segments of the capsule wall, the third stage comprising a hollow body that is generally cylindrical or is generally frustoconical having a third cone angle less than the second cone angle; the second stages being traversed by apertures to provide an air path from an exterior to an interior of the needle. The method preferably comprises the further step of generating a flow of air through the inlet needle, the pierced capsule and the outlet needle, thereby entraining powder from the capsule to be dispensed in the flow of air. In accordance with the invention, the first stage of the needle is a solid cone that forms a pointed tip of the needle and thereby ensures good initial piercing of the capsule, without presenting an axial opening that is liable to become blocked. The first stage preferably has a small cone angle to reduce its resistance to penetration of the capsule wall. The second stage of the needle may be generally frustoconical and have a second cone angle greater than the first cone angle, whereby, as the needle advances into the capsule, the second stage curls segments of the capsule end wall away from the axis of the needle. Preferably, the third stage of the needle is generally cylindrical or is generally frustoconical, having a third cone angle less than the second cone angle. The small cone angle of the third stage helps the needle the penetrate fully into the capsule, through the hole formed by the first and second stages, with a reduced risk of forming tears in the capsule wall. Accordingly, an effective seal may be formed between the capsule wall and the base of the third stage of the needle. As a result, no significant air path exists around the outside of the capsule and all air is forced to flow through the interior of the capsule, where it can serve the intended purpose of entraining powder. 11 06 24 If the outer diameter of the third stage is suitably chosen, it can press the curled segments of the capsule end wall flat against the internal side wall of the capsule to avoid creating cavities in which powder could be trapped. These functions of the second and third stage, to curl up segments of the capsule end wall and press them flat against the side wall, are particularly advantageous when the needle serves as the outlet needle, by which the airstream carrying entrained powder leaves the capsule. In that case, the third stage is preferably also traversed by apertures to provide an air path between the interior of the third stage and the exterior of the needle. The apertures of the second and third stages may be merged in order to minimize the obstruction that the needle presents to air leaving the capsule. In the present specification, “cone angle” refers to the acute angle between a conical surface and the axis of the cone. (In other contexts, this is sometimes referred to as the “half angle” of the cone.) The term “cone” is not limited to circular cones. It also encompasses cones that are elliptical, polygonal (i.e. pyramids) or more irregular in shape. In these alternative cases, the cone angle will vary about the axis. For the purposes of the present specification, the cone angle may be measured in any plane containing the axis. It is also not essential that the profile of the needle should consist only of straight-line sections so a “cone” should also be taken to encompass concave or convex curved surfaces that surround the axis and continuously increase (or remain constant) in diameter along the axis. For example, instead of a sharp change in angle between the stages of the needle, there could be a smoothly curved transition between them. In the case of a curved surface, a cone angle can be determined at any point from a line tangent to the surface at that point, in a plane containing the axis. The term “powder” is intended to encompass any solid or semi-solid material that is finely divided into particles that do not adhere to each other too strongly, whereby the particles are capable of being entrained in a stream of air or gas. The particles may be rounded or angular, regular or irregular, uniform or non-uniform in their size, shape and material. 11 06 24 As noted, one function of the needles according to the invention is to curl up segments of the capsule end wall and press them flat against the side wall. The word “curl” does not imply that the segments must bent though 360° to form a complete roll - although that outcome is also not excluded from protection. In practice, the curled segments 5 might be bent through no more than 90° to reorient them from being substantially radial in the capsule end wall to lying substantially parallel to the capsule side wall. Where the specification uses directional terms such as “upper”, “lower”, they refer to the orientation of the device shown in the drawings, with the axes of the needle 10 generally vertical and the outlet needle above the inlet needle. This is typical of how some embodiments of the invention may be used as a nasal inhaler. However, the invention is not limited to use in such an orientation and, of course, devices according to the invention may be manufactured, distributed and stored in any orientation while remaining within the scope of the claims. 15 The drawings Figure 1 is a partial section on the axis of a powder dispenser, before the capsule has been pierced, the dispenser incorporating an inlet needle and an outlet needle according to an embodiment of the present invention. 20 Figure 2 is a partial section on the axis of the powder dispenser of Figure 1, after the capsule has been pierced by the inlet needle and the outlet needle. Figure 3 is a side view in cross-section of the outlet needle of Figures 1 and 2. Figures 4a, 4b and 4c illustrate successive stages in the piercing of a powder capsule by the outlet needle of Figure 3. 25 Figure 5a is a section, viewed from the front, on the axis of the inlet needle of Figures 1 and 2. Figure 5b is a section, viewed from the side, on the axis of the inlet needle of Figure 5a. Figure 5c is a plan view of the inlet needle of Figure 5a. Figures 6a, 6b and 6c correspond to Figures 5a, 5b and 5c but show an inlet needle 30 according to a first alternative design. Figures 7a, 7b and 7c correspond to Figures 5a, 5b and 5c but show an inlet needle according to a second alternative design. 11 06 24 Figures 8a, 8b and 8c illustrate successive stages in the piercing of a powder capsule by the inlet needle of Figure 5a. Figure 1 shows part of a dispenser for dispensing powder from a capsule 2 into an airstream, for example forming part of a nasal inhaler. The capsule 2 is of a standard shape and size, comprising a side wall in the form of a hollow cylinder, which is closed by upper and lower end walls in the form of a dome or hemisphere. The capsule is supported between a first moving part 4 and a second moving part 6, the first and second moving parts 4,6 being capable of sliding towards one another parallel to an axis 8, which coincides with the axis of the capsule 2. In this embodiment, the capsule 2 is supported in a generally cylindrical capsule chamber 10 of the first moving part 4. The upper end of the capsule chamber 10 is open to allow insertion of the capsule 2. Its inner diameter is chosen to allow the capsule 2 to slide freely along the axis of the chamber 10 but to have no significant freedom of movement in a transverse direction. Before activation of the dispenser, the lower end wall of the capsule 2 rests on the tip of an upwardly pointing inlet needle 12, which lies on the axis 8 inside the capsule chamber 10. The second moving part 6 comprises a downwardly pointing outlet needle 14, which also lies on the axis 8. Before activation of the dispenser, the tip of the outlet needle 14 is poised just above the upper end wall of the capsule 2. It will be understood that in alternative embodiments (not illustrated), the capsule chamber could be provided on the second moving part 6 or the capsule 2 could be supported between the first and second moving parts 4,6. Figure 2 illustrates the dispenser of Figure 1 after it has been activated to move the first and second moving parts 4,6 closer together. It may be noted in Figure 1 that the second moving part 6 closely surrounds the outside of the capsule chamber 10 of the first moving part 4 so that the two parts already almost touch one another in the radial direction even before activation of the dispenser. When this specification refers to the parts 4,6 moving closer together, it refers to closeness only as measured in a direction parallel to the axis 8. It will also be understood that only relative movement between the first and second parts 4,6 is significant: it does not matter whether one part moves 11 06 24 while the other is stationary or whether the parts simultaneously move towards one another. In Figure 2, downward pressure from the outlet needle 14 has pushed the capsule 2 to the bottom of the capsule chamber 10. As a result, the inlet needle 12 has pierced the lower end wall of the capsule 2 and is now positioned substantially entirely inside the capsule 2. Further downward pressure has caused the outlet needle 14 to pierce the upper end wall of the capsule so the outlet needle 14 is also now positioned substantially entirely inside the capsule 2. As illustrated, the tip of the inlet needle 12 and the tip of the outlet needle 14 may approach one another so as to be almost touching. That is not important for the operation of the dispenser as such; rather, it permits the needles 12,14 to have the greatest possible length within the fixed length of the capsule 2, which in turn means that the needles - particularly the outlet needle 14 - can be configured to have a large outer diameter while maintaining a reasonable range of cone angles as discussed below. In other embodiments of the invention, for example designed for a capsule 2 of different proportions, there may remain a significant gap between the tips of the needles 12,14 even when the first and second parts have moved fully towards one another. As described in more detail below, the inlet and outlet needles 12,14 are hollow so that by piercing the capsule 2 they create an air path successively through the inlet needle 12, the capsule 2 and the outlet needle 14 to an outlet channel 16 in the second moving part 6. The outlet channel 16 may lead, for example, to the nozzle of an inhaler. When a stream of air is induced to flow along this path, the airstream entrains powder from the capsule 2 and carries it through the outlet channel 16 for delivery to the desired destination. For clarity, the powder is not shown in the drawings but the capsule 2 will initially contain a measured quantity of it, which may fill the capsule substantially entirely or only in part. Preferably, the first and second needles 12,14 substantially seal around the holes that they create at the respective ends of the capsule 2 while the capsule 2 fits fairly closely within the capsule chamber 10 so no significant flow of air is created around the outside of the capsule 2. 11 06 24 The present invention is not concerned with how the stream of air is generated. One possibility is that it may be generated by low pressure applied to the outlet channel 16, for example by a user inhaling sharply through the nozzle of an inhaler in which the dispenser is incorporated. Alternatively, it may be generated by high pressure upstream 5 of the inlet needle 12, supplied either from a source of pre-pressurized air or from a pump (not illustrated). If a pump is used, it may be operated directly by activation of the dispenser or be controlled independently. Figure 3 illustrates the outlet needle 14 in more detail. From the tip to the base it 10 comprises a first stage 18, a second stage 20 and a third stage 22, which in Figure 3 are demarcated by dashed horizontal lines. The first stage 18 is a solid cone that forms a pointed tip of the needle 14. It has a relatively small cone angle 0i to ensure that the initial piercing of the capsule 2 occurs cleanly without deforming the capsule end wall; but if the cone angle 0i is too small, the tip of the needle will be insufficiently robust 15 during manufacture, such as by injection moulding, and during use. For these reasons, a preferred range of the first cone angle is 15° <0i <24° with an optimum value of 0i = 19°. The second stage 20 of the outlet needle 14 comprises a hollow interior 24 and is 20 traversed by apertures 26 that provide an air path between the interior 24 and the exterior of the needle 14 (the exterior being located within the capsule 2 when the dispenser is in use). The second stage 20 is substantially frustoconical in shape such that its outer surface 28 is continuous with the outer surface of the first stage 18. The outer surface 28 may be formed by a set of ribs 30 disposed about the axis 8, which 25 define the apertures 26 between them. There are eight ribs in the illustrated example. The outer surface defines a second cone angle 02 that is preferably greater than the first cone angle 0i. For example, a preferred range of the second cone angle is 25° <02 <35° with an optimum value of 02 = 30°. The function of the second stage is, as the needle 14 is pushed into the capsule 2, to peel segments of the capsule end wall away from the 30 hole formed by the first stage 18, which process typically forms the segments into curls. The second cone angle 02 may be chosen to enhance this process but also to serve as a transition between the first and third cone angles 0i, 03. If sufficient length is available 11 06 24 in the capsule 2, then the second cone angle 02 may be reduced to approach or match the first cone angle 0i. It will be understood that the respective lengths and cone angles of the first, second and 5 third stages 18,20,22 cannot be chosen entirely independently. The overall length and the base diameter of the needle 14 are substantially determined by the fixed dimensions of the capsule 2. Within those constraints, the lengths and cone angles of the first, second and third stages 18,20,22 must be chosen such that the diameter of the outer surface 28 of the needle 14 increases continuously from the tip to the base diameter, 10 while transitioning successively through the first, second and third cone angles. In some embodiments of the outlet needle 14, the apertures 26 of the second stage 20 may extend almost to the tip of the needle. In that case, the first stage 18 will be very short, consisting essentially only of the solid volume where the ribs 30 that are discrete in the second stage 20 merge together to form the tip. 15 The third stage 22, closest to the base 32 of the outlet needle 14, comprises a continuation of the hollow interior 24 of the second stage 20. The hollow interior 24 is open to the base 32 to provide an air path from the needle 14 that is in communication with the outlet channel 16 of the dispenser. Like the second stage 20, the third stage 22 20 of the outlet needle 14 may also be traversed by apertures to provide an air path between the interior 24 and the exterior of the needle 12. The apertures are preferably continuous with the apertures 26 of the second stage, being defined between continuations of the ribs 30 of the second stage, so that the second and third stages form a cage-like structure. Once powder from the capsule 2 has been entrained in the 25 airstream, it is desirable that the air should be able to flow as easily as possible through the outlet needle 14, with the minimum of obstructions that might cause the air to slow and release its load. The continuous apertures 26 between the longitudinally aligned ribs 30 of the second and third stages allow the air to flow substantially straight and generally parallel to the axis 8 from the interior of the capsule 2 into the outlet 30 channel 16. The third stage 22 preferably comprises a continuous ring 34 of material around the circumference of the base 32 to provide structural stability to the needle 14. 11 06 24 The third stage 22 serves a further function, which is to compress the curls of capsule end wall that were formed by the second stage 20 and flatten them against the interior of the side wall of the capsule. This substantially eliminates voids that would otherwise be present inside the curls and that might provide locations for some of the powder to 5 lodge and thereby fail to be dispensed fully from the capsule 2. For this reason, the outer diameter of the third stage 22, at least close to the base 32, should be only slightly smaller than the diameter of the capsule 2. For example, if the outer diameter of a standard capsule is nominally 5.60mm and its wall thickness is nominally 0.1mm, then the basal diameter of the third stage 22 may be 5.00mm, which allows space at each 10 end of the diameter for a double wall thickness and a small gap. For the outer surface of the third stage to flatten the curls effectively against the side wall, the third cone angle 03 should be less - preferably much less - than the second cone angle. It may in fact be zero so that the outer surface is parallel to the cylindrical side wall of the capsule and it preferably lies in the range 0° <03 <9°, with an optimum value of 03 = 4°. 15 In some cases, it may be expected that the curls of the capsule wall that have been compressed against the outer surface of the third stage 22 will substantially block the apertures 26 in the third stage. In such cases, the apertures 26 may be omitted from the third stage of the needle 14 without any significant loss of function, being provided 20 only in the second stage 20. Figures 4a to 4c illustrate the successive steps in the piercing of the upper end wall of the capsule 2 by the outlet needle 14. In Figure 4a, the needle 14 advances from the position shown in Figure 1 so that the sharply pointed first stage 18 of the needle pierces 25 the end of the capsule 2 to form a small hole or initial tear. One or more regions or segments 36 of the capsule wall are folded away from the axis into the interior of the capsule 2. In Figure 4b, the needle 14 advances further and its second stage 20, with a greater 30 diameter and a greater cone angle than the first stage, enlarges the hole or the tears between the segments and peels the segments back from the axis 8, forming them into loose curls 38 of material. 11 06 24 In Figure 4c, the needle 14 advances to its final position and the third stage 22, which has a still greater diameter but a smaller cone angle than the second stage 20, flattens the curls 38 against the side wall of the capsule 2 so that powder cannot become trapped 5 in them. Figures 5a to 5c show three different views of the inlet needle 12 of the dispenser of Figures 1 and 2. Like the outlet needle 14, from the tip to the base the inlet needle 12 comprises a first stage 48, a second stage 50 and a third stage 52, which in the figures 10 are demarcated by dashed horizontal lines. Again, the outer diameter of the inlet needle 12 increases continuously from its tip to its base, while transitioning successively through the first, second and third cone angles (which are not necessarily different from each other). 15 The first stage 48 of the inlet needle 12 is a solid cone that forms a pointed tip of the needle. It has a relatively small cone angle 0i to ensure that the initial piercing of the capsule 2 occurs cleanly without deforming the capsule end wall; but if the cone angle 0i is too small, the tip of the needle will be insufficiently robust during moulding and during use. For these reasons, a preferred range of the first cone angle is 20 17° <0i <27° with an optimum value of 0i = 21°. In some applications, it may be important to determine the order in which the inlet needle 12 and the outlet needle 14 pierce the capsule 2 as the first and second moving parts 4,6 move closer together. If so, the relative sizes of the needles’ respective first cone angles 0i may be chosen so that the needle with the smaller cone angle (i.e. with the sharper tip) will pierce the 25 capsule 2 first. The second stage 50 of the inlet needle 12 comprises a hollow interior 54 and is traversed by apertures 56 that provide an air path between the interior 54 and the exterior of the needle 12 (the exterior being located within the capsule 2 when the 30 dispenser is in use). The second stage 50 has an outer surface 58 that is continuous with the outer surface of the first stage 48. 11 06 24 The third stage 52 comprises a continuation of the hollow interior 54 of the second stage 50. The hollow interior 54 takes the form of a blind bore, which extends axially in a direction from the base 56 towards the tip of the needle 12. This provides an air path into the needle 12 that is in communication with a source of pressurized air to the 5 dispenser (not shown). Unlike the outlet needle 14, the third stage 52 of the illustrated inlet needle 12 is not traversed by apertures so there is no direct air path between the interior 54 of the third stage and the radially outer surface 58. When the dispenser is used in the orientation shown in Figure 5, the powder will rest in the bottom of the capsule 2 against the outer surface 58 of the inlet needle 12. If apertures were provided 1 o in the third stage 52, they would provide a route via which the powder might fall out of the capsule 2 via the hollow interior 54 of the needle 12 and thereby fail to be delivered to the user when the dispenser is activated. The cone angle 03 of the third stage 52 is smaller than the cone angle 0i of the first 15 stage 48. The third cone angle 03 preferably lies in the range 0° <03 <9°, with an optimum value close to zero so that the outer surface of the third stage 52 is substantially cylindrical, in order to offer at most a small resistance to the insertion of the needle 12 fully into the capsule 2. 20 As previously noted, the second stage 50 of the inlet needle 12 is traversed by apertures between the hollow interior 54 and the exterior. In the needle illustrated in Figures 5a to 5c, there are two such apertures 56, located diametrically opposite one another. Alternative designs of the inlet needle could comprise a single aperture or more than two apertures angularly distributed about the axis 8 of the needle. For example, 25 Figures 6a to 6c are essentially identical to Figures 5a to 5c, except that they show three of the apertures 56. The apertures 56 are preferably oriented substantially radially to the axis 8 so that they create an unobstructed air path from the interior to the exterior in a direction 30 perpendicular to the axis 8, as seen in Figure 5a. A flat or slightly concave end wall 60 of the blind bore 54 will obstruct the flow of air through the needle 12 parallel to the axis 8 and divert the air through the apertures 56 into the capsule 2. This will create a 11 06 24 turbulent airstream that swirls around inside the capsule 2 and entrains powder in the capsule, including powder that is below the apertures 56, resting against the outer surface 58 of the third stage 52. The diameter of the inlet needle 12 is a typically smaller than the diameter of the outlet needle 14 to allow room for the powder to rest 5 at the bottom of the capsule 2 and for the airstream to circulate through it. For ease and cheapness of manufacture, the inlet needle 12 is preferably formed by moulding, e.g. from a plastic material. The needles illustrated in Figures 5 and 6 are designed to be capable of being formed in a simple mould, which comprises only two 10 mould parts (not illustrated) that can be separated in opposite axial directions. This is contrary to the expected requirement for forming the radially orientated apertures 56. A first mould part forms the blind bore 54 that defines the hollow interior of the second and third stages and it is removed in the downward direction of Figure 5a. A second mould part forms the capsule chamber 10 and the outer surface 58 of the inlet needle 12 15 and it is removed in the upward direction of Figure 5a. This second mould part includes features that form “cut-outs” or voids 62 at angular positions around the second stage 50 of the inlet needle 12. These voids extend axially from the external surface 58 of the second stage 50 towards the base of the needle and they intersect the interior bore 54 for a distance below its end wall 60 to create the radially orientated 20 apertures 56. From the references to moulding, it should be clear that the terms “bore” and “cut-outs” should not be taken to imply that those features are typically formed by boring, cutting or other machining operations to remove pre-existing material. 25 Figures 7a to 7c illustrate an inlet needle 12 that again has two radial apertures 56, located diametrically opposite one another. In this case, they have a simpler form, being opposite ends of a common, transverse bore 64. This simpler form comes at the expense of a more complex moulding process, which will require at least one additional mould part (not illustrated) to be removed in the transverse direction, along the axis of 30 the bore 64. 11 06 24 The second stage 50 of the inlet needle 12 preferably has a cone angle (or angles) 02 intermediate between the first and third cone angles 0i, 63 so as to provide a transition between the sharply conical first stage 48 and the near-cylindrical third stage 52. The axial location of the boundary plane demarcating the first and second stages 48,50 is 5 somewhat arbitrary, provided that the first stage 48 includes the solid conical tip of the needle 12 and the second stage 50 includes the radial apertures 56. In Figure 5a, the boundary is drawn such that the first stage 48 comprises a pure, circular cone. As a result, the second stage 50 comprises a change of cone angle 02 from an upper cone angle that matches the first stage to a lower cone angle that matches the third stage. 10 This is best seen in Figure 5b; the apparently larger angle seen in the voids 62 in Figure 5a lies in a plane that does not coincide with the axis 8 and therefore does not represent a true cone angle of the outer surface 58. Unlike in the outlet needle 14, the second stage 50 of the inlet needle 12 generally does not need to have a second cone angle 02 that is greater than the first angle 0i. The purpose of that broader cone in the 15 outlet needle 14 is to control the formation of the curled segments 36 of the capsule wall but, because of the turbulent environment surrounding the inlet needle 12, there is a much reduced risk that powder may become trapped if such curls form at the inlet end of the capsule 2. 20 Figures 8a to 8c illustrate the successive steps in the piercing of the lower end wall of the capsule 2 by the inlet needle 12. In Figure 8a, the needle 12 advances from the position shown in Figure 1 so that the sharply pointed first stage 48 of the needle pierces the end of the capsule 2 to form a small hole or initial tear. One or more regions or segments 36 of the capsule wall are folded away from the axis 8 into the interior of the 25 capsule 2. In Figure 8b, the needle 12 advances further and its second stage 50, with a greater diameter than the first stage 48, enlarges the hole or the tears between the segments 36 and peels the segments back from the axis 8. To this point, the process is very similar 30 to the piercing of the capsule 2 by the outlet needle 14, illustrated in Figures 4a and 4b. 11 06 24 In Figure 8c, the needle 12 advances to its final position and the third stage 52, which has a small cone angle such that it may be substantially cylindrical, pushes through the hole already formed in the capsule wall. As a result of its small cone angle, the third stage 52 does not significantly enlarge the hole created by the first and second 5 stages 48,50 but it pushes further into the hole to form an effective seal against the capsule wall around the edge of the hole. The inlet needle 12 is then positioned fully within the capsule 2 and, in particular, the apertures 56 of the second stage are spaced from the bottom of the capsule. In the illustrated powder dispenser, the inlet needle 12 differs from the outlet needle 14 in having a smaller outer diameter, which is 10 significantly less than the inner diameter of the capsule 2. As a result, the inlet needle 12 does not flatten the segments 36 against the side wall of the capsule 2. The curled segments 36 of the capsule wall rest against the outer surface 58 of the third stage 52 of the needle 12 so that they do not significantly obstruct the radial apertures 56 of the second stage. 15 For reasons of simplicity and economy, the inlet and outlet needles 12,14 may be formed by moulding them integrally with the first and second moving parts 4,6 respectively. However, the invention does not exclude needles that are formed as separate components. 20 20 02 25

Claims

1. A needle for piercing a capsule of powder, wherein:the needle comprises a first stage, a second stage and third stage;the first stage is a solid cone that forms a pointed tip of the needle, the first stage having a first cone angle;the second stage comprises a hollow interior and is traversed by apertures that provide an air path between the interior and an exterior of the needle, the second stage being generally frustoconical and having a second cone angle greater than the first cone angle; andthe third stage comprises a hollow interior that provides an air path between the interior of the second stage and a base of the needle, the third stage being generally cylindrical or generally frustoconical and having a third cone angle less than the second cone angle.

2. A needle according to claim 1, wherein:the third stage is also traversed by apertures to provide an air path between the interior of the third stage and the exterior of the needle.

3. A needle according to claim 2, wherein the second and third stages of the needle comprise a cage structure formed by a plurality of ribs that each extend from the first stage to the base of the needle, the apertures being defined by gaps between adjacent ribs.

4. A needle according to any preceding claim, wherein the first cone angle is greater than or equal to 15 degrees and is less than or equal to 24 degrees.

5. A needle according to any preceding claim, wherein the third cone angle is greater than 0 degrees and is less than or equal to 9 degrees.

6. A needle according to any preceding claim, which is part of a powder dispenser in which the capsule can be supported.20 02 257. A powder di spenser compri sing:a first part comprising a hollow inlet needle;a second part comprising a hollow outlet needle, the inlet and outlet needles opposing one another along an axis; andmeans for supporting a powder capsule on the axis between the inlet and outlet needles;the first and second parts being movable towards one another to cause the inlet and outlet needles to pierce the capsule;wherein the outlet needle is a needle according to any of claims 1 to 5.

8. A dispenser according to claim 7, further comprising means for generating a flow of air through the inlet needle, the pierced capsule and the outlet needle, thereby entraining powder from the capsule to be dispensed in the flow of air.

9. A method of piercing a powder capsule in a powder dispenser, the method comprising the steps ofsupporting the powder capsule on an axis between a first part comprising a hollow inlet needle and a second part comprising a hollow outlet needle, the inlet and outlet needles opposing one another along the axis; andmoving the first and second parts towards one another to cause the inlet and outlet needles to pierce the capsule;wherein, as the first and second parts move towards one another:a first stage of the outlet needle forms an initial opening in a wall of the capsule, the first stage comprising a solid cone that has a first cone angle and forms a tip of the needle,a second stage of the outlet needle curls segments of the capsule wall away from the initial opening, the second stage comprising a hollow, generally frustoconical body that has a second cone angle greater than the first cone angle; anda third stage of the outlet needle radially compresses the curled segments of the capsule wall, the third stage comprising a hollow body that is generally cylindrical or is generally frustoconical having a third cone angle less than the second cone angle;the second stages being traversed by apertures to provide an air path from an exterior to an interior of the needle.

10. A method according to claim 9, comprising the further step of generating a flow of air through the inlet needle, the pierced capsule and the outlet needle, thereby entraining powder from the capsule to be dispensed in the flow of air.20 02 25

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