3d printed ballscrew

Abstract

A ballnut 10, 100 for a ballscrew 1, a ballscrew 1 and a method of manufacturing a ballnut (10 fig. 1) for a ballscrew (1) comprises a 3D printed housing 20 with a radially inner surface 22 for receiving a ballscrew shaft (2). The housing having a helical groove 30 defined at least in part by the radially inner surface of the housing. The housing has at least one recirculation path 40 where the helical groove and recirculation path are connected by a first transition region 60 at a first end of the recirculation path and a first end of the helical groove, and a second transition region 70 at a second end of the recirculation path 40 and a second end of the helical groove. The helical groove, the recirculation path and the first and second transition regions form a circuit for a rolling bearing (4 fig. 4) to travel along when the ballnut is connected to the ballscrew shaft. The first and / or second transition region define a continuous path between the helical groove and the recirculation path 40. The housing maybe manufactured in on-piece as a unitary component.

Description

Field of the Invention. The present disclosure relates to a 3D printed ballscrew. Aspects of the invention relate to a ballnut for a ballscrew, a ballscrew and a method of manufacturing a ballnut for a ballscrew. Background to the Invention Ballscrews are used where there is a requirement to convert rotational movement into a linear movement. The low friction in ballscrews is particularly advantageous in relation to alternative mechanical devices, such lead screws, which are less efficient at conversion of rotary motion to a linear one. Ballscrews comprise a shaft (or screw) and a ballnut. The ballnut in use recirculates a number of ball bearings. The ball bearings engage with the "screw" or "shaft" of the ballscrew. The manner of this engagement is dictated by raceways or tracks on the inner surface of the ballnut and outer surface of the shaft (the helical grove on the screw shaft). The raceways follow a helical path that forms part of a recirculation circuit. The circuit often has an 'insert' added to complete a recirculation circuit. Inserts are manufactured separately to the ballnut and are fitted into the ballnut to complete part of the recirculation circuit. This is because it is not possible to machine the internal channels of the recirculation circuit using machining methods. Alternatively, the recirculation of the ball bearings occurs by means of a pipe or ducting which returns ball bearings to the start of the circuit. When all parts of the ballscrew engage together, the movement of ball bearing following a helical path has the effect of converting between rotary and linear motion. For example, the shaft can be rotated and the ball nut will move linearly along the shaft. Ballscrews are currently utilised in a variety of demanding applications. One example is in commercial aerospace applications to control the actuation of wing flaps or movement of nacelles. Often however, heavy roller screws are used instead of ballscrews in commercial aerospace applications due to roller screws being longer and therefore enabling more points of contact and greater distribution of force. Other examples include their use to deploy components in or on satellites, or for controlling components on racing cars. For satellite applications, in particular, the vibrational loading experienced during launch can dislodge inserts. As ballscrews often actuate mission critical components the dislodgement of an insert can stop the satellite functioning as intended and therefore reduce useable life of the satellite itself. It is an aim of the present invention to improve on ballscrews of the prior art. Summary of the Invention Aspects and embodiments of the invention relate to a ballnut for a ballscrew, a ballscrew and a method of manufacturing a ballnut for a ballscrew as claimed in the appended claims. According to an aspect of the invention, there is provided a ballnut for a ballscrew having a ballscrew shaft. The ballnut comprises: a 3D printed housing with a radially inner surface for receiving a ballscrew shaft; the housing having at least one helical groove defined at least in part by the radially inner surface of the housing; the housing having at least one recirculation path; the at least one helical groove and at least one recirculation path are connected by a first transition region at a first end of the recirculation path and a first end of the at least one helical groove, and a second transition region at a second end of the recirculation path and a second end of the at least one helical groove; wherein the at least one helical groove, the at least one recirculation path and the first and second transition regions form a circuit for a rolling bearing to travel along when the ballnut is connected to a ballscrew shaft; and the first and / or second transition region define a continuous path between the at least one helical groove and the at least one recirculation path. The ballnut is advantageously manufactured using 3d-printing by doing so the whole component may be manufactured in a single print session resulting in a simplified manufacturing procedure. The rolling bearing may travel along the circuit in either direction in use. The advantage of using 3D printing is that the housing can have a smooth transition region or regions into and or out of the recirculation path. In prior art systems the provision of a stepped transition region means that the rolling bearings are not taking the load when they fall into the recirculation path or out of the recirculation path. This is because a wall of the circuit and the ballscrew shaft's helical groove are not holding the rolling bearing between them. The ball bearing is therefore free to rattle in a stepped transition region, this rattling can have a negative impact on the structure of the ballscrew in use as fatigue life could be decreased. It also increases and vibration and / or noise in components which may not be wanted in certain applications where low vibration or near soundless running is required. The present invention by comparison does not suffer from the adverse effect of ball bearing rattle to the same degree (if at all) as the continuous transition between the recirculation path and the helical groove is one which cradles the rolling bearing in use confining its movement to be along the circuit and instead of laterally. The rolling bearing may be a ball bearing or a roller bearing. Roller bearings are cylindrical shaped bearings and increase the contact point between the housing and the bearing and thus enable greater loads to be taken. By utilising 3D printing different shaped rolling bearings may be utilised than are otherwise previously possible via traditional reductive manufacturing techniques. The first and / or second transition regions define a continuous path suitable for enabling the ball bearing to transition between the at least one helical groove and the recirculation path with the rolling bearing remaining in contact with a housing wall throughout the length of the first and / or second transition region(s). The first and / or second transition regions define a continuous path and therefore not a contiguous path. That is, a path in a transition region which is adjacent but not directly connected or unitary with the helical groove itself. A contiguous path would simply abut the helical groove without being directly connected to it. Preferably, the first and / or second transition regions are part of the recirculation path. Preferably, the continuous path is a smooth path. The continuous path is smooth in that there is no sudden change or gap from the helical path to the recirculation path or vice versa. The continuous path cradles the rolling bearing in use reducing the likelihood of rattle. Preferably, the continuous path is a non-stepped path. As the path is non-stepped there is a greater packing factor of rolling bearings within the circuit as space does not need to be provided to enable the rolling bearing to fall down the stepped transition in a nonstepped smooth path. Preferably, the continuous path is a substantially curved path in cross-section. By providing a curved path there is no sharp transition between the helical groove and recirculation path which could cause the rolling bearings to become stuck in use. Preferably, the housing is manufactured as a unitary component. Manufacturing as a single (unitary) component reduces the potential of any vibration detrimentally effecting the ballscrew in use. Ballscrews are traditionally manufactured in at least two parts. By having a single unitary ballnut without a manufacturing step of joining the two components together there is a removal of a potential failure point of the ballscrew which may come loose during high vibrational loading. Preferably, the ballnut does not comprise an insert forming a part of: the at least one recirculation path, or helical path, first or second transition region, or circuit. Previously, ballnuts comprised an insert which forms part of the recirculation path where the recirculation of the balls happens through the housing. By having a recirculation path which is entirely defined by the unitary housing then the impact of vibration on the ballscrew assembly is reduced in use as there is no insert which could become unattached from the ballnut causing failure of the ballscrew. Preferably, the at least one recirculation path is contained within the housing. Previously, ballnuts which did not have an insert had an external recirculation path in the form of tubing or pipework to feed rolling bearings back to the start of the rolling bearing circuit. A potential downside of this is that this requires an additional component to be connected to the housing which could become damaged in use or fall off due to vibrational loading on the ballscrew in use. By providing the recirculation path within the housing the housing protects the recirculation path from damage and provides a more compact form factor. The provision of a more compact ballnut without an external recirculation path. Preferably, the recirculation path is completely contained within the housing. Preferably, a portion of the at least one recirculation path is S-shaped. An S-shaped path is efficient for removing the rolling bearing from the end of a helical groove and returning the rolling bearing to the start of the helical groove (or the start of a different helical groove). An S-shaped path can be more easily manufactured using 3D printing rather than traditional manufacturing methods such as turning on a lathe. Preferably, the helical groove comprises a guiding lip. The guiding lip guides the rolling bearing in use into the screw threads of the shaft reducing the amount of lateral movement of the rolling bearing. More preferably, the guiding lip retains at least a portion of the rolling bearing. The guiding lip retains at least a portion of the rolling bearing to prevent the rolling bearing from falling out or otherwise becoming disengaged from the housing. Preferably the ballnut has two circuits. Preferably the ballnut has three circuits. Preferably the ballnut has four circuits. Preferably the ballnut has two to four circuits. Preferably the ballnut has a plurality of circuits. Preferably, wherein the recirculation paths of each circuit are offset equally around the circumference of the radially inner surface of the housing in respect of each other. Equally distributing the recirculation paths around the circumference aids in the balance of the ballnut and ballscrew in use. Preferably, the recirculation path of each circuit is offset by an azimuthal angle (9) in degrees of 9 = 369 / n, where n is the number of circuits, with respect of each other. Offsetting each of the recirculation paths by the angle 9 aids in balancing the ballnut in practice by distributing the weight of the rolling bearings around the ballnut. Preferably, the radially inner surface is a through bore with a diameter of 2 mm to 29 mm. By utilising a 3D printing technique a smaller ballscrew can be manufactured than has been previously possible. The ballnut manufactured by 3D printing can be made to be very small such that the through bore has a diameter of 2 mm to 29 mm this enables ballscrews to be utilised in applications where they were not previously able to be used, for example in miniaturised devices. Preferably, the housing is 3D printed from one of: a metal, a plastic, or a composite or a ceramic. Preferably, the metal is any one of: an aluminium ally, a steel, a stainless steel, a cobalt chrome alloy, a titanium alloy, a nickel alloy, copper, a copper alloy, a refractory metal, a precious metal, or precious metal alloy. Preferably one or more of the: at least one helical groove, at least one recirculation path, first transition region and second transition region comprise: a "V" shaped wall or an approximately semi-circular cross-section wall. A "V" shaped wall or approximately semicircular cross-sectional wall is particularly useful with ball bearing type roller bearings. Alternatively, the helical groove may have a square or rectangular shaped wall. A square or rectangular shaped wall is particularly useful for use with roller bearings which increase the contact point between the housing and the bearing and thus enable greater loads to be taken. This increases the efficiency of the ball screw. Utilising 3D printing enables cylindrical bearings to be used as there is no discontinuity in the continuous path of the circuit that could prevent the cylinder from rolling. Using roller bearings enables an elimination of back drive whilst maintaining efficiency of the ballscrew in use. The rolling bearing may be one of: a ball bearing and a roller bearing. According to another aspect of the invention a ballscrew is provided. The ballscrew comprising a ballnut according to any embodiment of the previous aspect and a ballscrew shaft. According to a further aspect of the invention a method of manufacturing a ballnut for a ballscrew having a ballscrew shaft is provided. The method comprising the steps of: manufacturing a ballnut housing by 3d-printing, the housing having a radially inner surface for receiving a ballscrew shaft; the housing having at least one helical groove defined at least in part by the radially inner surface of the housing; the housing having at least one recirculation path; the at least one helical groove and at least one recirculation path are connected by a first transition region at a first end of the recirculation path and a first end of the at least one helical groove, and a second transition region at a second end of the recirculation path and a second end of the at least one helical groove; wherein the at least one helical groove, the at least one recirculation path and the first and second transition regions form a circuit for a rolling bearing to travel along when the ballnut is connected to a ballscrew shaft; and the first and / or second transition region define a continuous path between the at least one helical groove and the at least one recirculation path. Preferably, the housing is manufactured as a unitary component. Description of the Figures Figure 1 shows a schematic representation of a ballscrew according to the present invention; Figure 2 is a ballnut according to the present invention; Figure 3 is a cross-sectional view through the ballnut of figure 2; Figure 4 is a figure showing the movement of ball bearings in the ballnut as the ballscrew moves; Figure 5 is a schematic diagram showing an end on view of a ballnut and movement of ball bearings within the ballnut; Figure 6 is an alternative ball nut with two circuits shown in cross-section; and Figure 7 is an alternative cross-sectional view of the ballnut of Figure 6. Detailed Description The invention will be described with the aid of Figures 1 to 7. Figure 1 shows a ballscrew 1 comprising a ballnut 10, a plurality of rolling bearings (ball bearings 4) and a screw shaft 2. Rotation of the shaft 2 about an axis of rotation a causes linear movement of the ballnut 10 along the axis X. In this way, the ballscrew 1 converts rotational movement to a linear movement. Whilst the embodiments depicted show rolling bearings as ball bearings 4 it is envisioned that the roller bearings may alternatively be roller bearings. The ballnut 10 will now be described in detail with the aid of Figures 2 to 4. The ballnut 10 has a housing 20. The housing 20 shown in Figure 2 is annular and comprises a through bore 26 with a radially inner surface 22. The outer surface of the housing 20 is a radially outer surface 24. The bore 26 and radially inner surface 22 are adapted to receive the ballscrew shaft 2. Figure 2 shows the ballnut 10 on a cylindrical coordinate system. The centreline of the bore 26 defines the longitudinal axis X along which the ballnut 10 moves in use. Alternative configurations or shapes of the ballnut 10 are possible, such as a cuboid or cube or other such shape. The annular cylinder ballnut 10 shown in the Figures is not limiting and other shapes are plausible so long as the inner surface 22 is adapted to receive a shaft 2. Moreover, the ballnut 10 may optionally be further configured to have a through bore through the housing to slidably receive a guide rail or guide rod. The guide rail or guide rod is used to constrain movement of the ballnut 10 to along the axis X and reduce or eliminate any rotation of the ballnut 10 itself in practice. Disposed on the inner surface 22 of the housing 20 is a helical groove 30. The helical groove 30 is sized to receive the ball bearings 4 that enable the ballnut 10 to move along the shaft 2 in use as the shaft 2 turns. The helical groove 30 is defined, at least in part, by the inner surface 22 of the housing 20 as is shown in Figure 2. The helical groove 20 is recessed into a wall of the housing 20. The helical groove 30 is complementary to the shape of grooves on the shaft 2. In use, the helical groove 30 and grooves of the ballscrew shaft 2 cradle the ball bearing 4 between them providing a surface along which the ball bearing can move along. The helical groove 30 extends around the inner surface 22 from a start 32 to an end 34, as shown in Figures 3 to 5. The start 32 and end 34 are connected together by a recirculation path 40. The recirculation path 40 returns ball bearings 4 from the end 34 of the helical groove 30 to the start 32 of the helical groove 30 once they have reached the end 34 of the helical groove 30. As shown in Figures 4 and 5 the recirculation path has an inner wall 42 and an outer wall 44. The distance between the inner wall 42 and outer wall 44 is at least sufficient for the ball bearing 4 to move along, for example the diameter, D, of the ball bearing 4 plus a manufacturing tolerance such as 1 to 5 % of the Diameter. By providing such an arrangement there is a reduction in the rattling of the assembly associated with ball bearings not being packed into a ball nut sufficiently. The recirculation path 40 shown in Figures 2 and 3 is S-shaped or sinusoidal. The recirculation path 40 may alternatively be linear or zig-zagged or curved or another suitable path shape to connect the end 34 to the start 32. Cured or S-shaped paths provide paths with decreased rolling resistance as compared to a zig-zag type path as the smoother change in angle is less disruptive to the movement of the ball bearing 4. The helical groove 30 and recirculation path 40 are connected by a first transition region 60 at a first end of the recirculation path and a first end of the at least one helical groove 30 and a second transition region 70 at a second end of the recirculation path 40 and a second end of the at least one helical groove 30 as is shown in Figures 4 and 5. The first and second transient regions 60, 70 are part of the recirculation path 40. The helical groove 30 and recirculation path 40 together form one circuit 50. The circuit 50 is a path along which the ball bearings 4 travel along and return to their origin (in respect to an unactuated state prior to the shaft moving). This origin is located at an azimuthal angle 0o and the ball bearing 4 undertakes at least one full turn around the circumference of the inner surface 22 (or more than one turn where the helical groove 30 is longer than the circumference of the inner surface 22). The azimuthal angle 0C indicates one full turn around the circumference. The ballnut 10 shown in Figure 2 and 3 has four circuits 50. Figures 2 and 3 show that the circuits 50 are axially offset along a length L of the ballnut 10. The circuits 50 are not connected. Each circuit 50 in Figures 3 and 4 are unconnected and are the ball bearings 4 cannot move between each circuit 50. In alternative configurations, the ballnut 10 may have one circuit, two circuits, three circuits, four circuits, five circuits, six circuits, or more circuits, or a plurality of circuits, or any range or subset thereof. For example, an alternative ballnut 10 may have one or more circuits 50 which comprises multiple turns of the helical groove 30. Figure 4 shows a single circuit 50 in an 'unwrapped' form following the azimuthal angle 0 (in degrees or radians) on the x-axis. On the y-axis is the radius, r, from the centreline of the housing 20 at ro (co-axial with the centreline of the shaft 2) to the outer circumference, rc, of the housing 20. The interface between the shaft 2 and the ballnut 10 is along the dotted line at rs, rs corresponds to the location of the inner surface 22 and therefore the interface between the shaft 2 and ballnut 10. As can be seen from Figure 4, the circuit 50 is recessed into the housing 20 along the recirculation path 40 between the end 34 and the start 32 of the helical groove 30. Along the recirculation path the ball bearings 4 are removed from engagement with the screw 2 and in effect lifted away from the threads of the screw until they are placed back in the thread of the screw at a second point as is known in the art. The transition regions 60, 70 are continuous paths which enable the ball bearings to roll along and transition out of the helical groove into the recirculation path 40 through the end 34 and transition back into the helical groove 30 from the recirculation path 40 at the start 32. This arrangement is shown schematically in Figures 4 and 5. Figure 5 shows the circuit 50 on the same plane for reasons of clarity. As will be apparent to the skilled reader of this disclosure the start 32 and end 34 are located at different axial positions along the length of the housing axis apparent from Figure 3. The transition region 60, 70 increases the distance of the inner wall 42 depth of the circuit 50 in relation to roas is seen by comparing the outer wall 38 with the transition to the outer wall 44 of the recirculation path. The continuous path is a path which is not interrupted, for example by any one or combination of: a gap, or a step, or a drop, or other interruption. The continuous path is a smooth path in the sense that the path does not have any one or combination of: a gap, or a step, or a drop, or other interruption. Another interruption which is not continuous or smooth may be an elbow where two linear tracks or paths meet in a "V" shape. The elbow may have a sharp angle which could cause a ball bearing to become stuck in the bottom of the "V" in use. The smooth path may comprise an outer wall 44 that varies in its radial depth within the housing 20 as shown in Figure 4 and 5. Prior art systems have recirculation circuits with transition regions which must be manufactured via reductive manufacturing processes which necessitate the removal of physical media. It is not possible to produce a continuous, curved and / or non-stepped path in the manner of the present disclosure using such reductive manufacturing methods because it is not possible to mill or drill a curved path into a ballnut housing as milling or drilling bits are only able to cut in a linear fashion. The manufacturing of the ballnut 10 via 3D priting is particularly advantageous as it enables the continuous path to be produced. The ballnut 10 has a guiding lip 36, the guiding lip. The guiding lip 36 assists in retaining the ball bearings 4 within the ballnut 10 and reduces the lateral movement of the ball bearings 4 within the ballnut 10. The guiding lip may be located at a distance D / 2 from the outer wall 38 of the groove and / or outer wall 44, where D is the diameter of the ball bearing 4. A two circuit ballnut 100 is shown in Figures 6 and 7. The two circuit ballnut 100 is substantially the same as the four-circuit variant of ballnut 10. As such, similar reference numerals have been utilised to show similar features. The housing 20 is manufactured using 3D printing. The 3D printing method is one known in the art, for example it may be any one of: stereolithography, selective laser sintering, fused deposition modelling, digital light process, multi jet fusion, polyjet, direct metal laser sintering, electron beam melting, paste extrusion, binder jetting, photo polymerization, nano-particle jetting, or other suitable 3D printing methods known in the art. The housing 20 is manufactured as a unitary component. Some post-manufacturing steps are potentially undertaken after the 3D printing step to remove supports and or polish surfaces (for example). The housing 20 being manufactured as a single unitary component means that the circuits 50 are manufactured to be within the housing 20 without the need for any cutting or machining processes subsequent to a bore being drilled as is the case in traditional manufacturing of ball screws. The bore 26 has a diameter of 2 to 20 mm. The housing 20 has an outer diameter of 10 to 50 mm. As such, the ballnut 10 is considered to be a 'micro' or 'miniaturised' ballscrew 1. The 3D printing methodology of the present invention is particularly suited to manufacture miniaturised ballscrews 1 which can be used in specialised applications where traditional manufacturing methods would not be possible to produce such a small ballscrew 1. A 'micro' or 'miniaturised' ballscrew 1 is particularly advantageous for controlling small machinery such as medical devices. The bore 26 may have a diameter of 2 to 10 mm or 10 to 20 mm or 2 mm or 3 mm or 4 mm or 5 mm or 6 mm or 7 mm or 8 mm or 9 mm or 10 mm or 11 mm or 12 mm or 13 mm or 14 mm or 15 mm or 16 mm or 17 mm or 18 mm or 19 mm or 20 mm or any range, combination or subset thereof. Alternatively, the bore 26 has a diameter of 20 mm to 100 mm. The housing 20 has an outer diameter 30 mm to 200 mm. The 3D printing technique is also able to produce longer ballnuts 10 which can be used in long ballscrews where traditionally two or more housings have had to be connected together due to limitations of machining grooves on prior ballscrews. The 3D printed housing 20 does not require multiple housings 20 to be connected. Instead, a single unitary housing 20 may be manufactured. The housing 20 can therefore have any length L required by the end use of the ballscrew 1. For example the length may be 10 mm to 1000 mm or 50 mm to 500 mm or 100 mm to 250 mm or any range, combination or subset thereof. By manufacturing the housing 20 layer by layer using a 3D printing process internal channels can be produced with complex structures which would not be possible to achieve using traditional methodologies. The material used to 3D print the ballnut may be a metal, a ceramic, a polymer, a composite, a plastic or any other material suitable for 3D printing. The 3D printable material may be manufactured using a commercially available 3D printable feedstock or powder or filament, or wire, or other usable feedstock. The 3D printable metal may be any one of or combination of: an aluminium ally, a steel, a cobalt chrome alloy, a titanium alloy, a nickel alloy, copper, a copper alloy, a refractory metal (such as Tungsten), a precious metal, or precious metal alloy. The aluminium alloy may be one of: AISilOMg, AISi7Mg0.6, AISi9Cu3, or other aluminium alloy suitable for 3D printing. The steel alloy may be one of: a stainless steel, 316L stainless steel, 15-5 PH stainless steel, 17-4 PH stainless steel, maraging steel, a case hardening steel, a tool steel. The cobalt chrome metal alloy may be a cobalt chrome material suitable for medical application. For example, the cobalt chrome alloy may be a biocompatible alloy. The cobalt chrome may be an MP1 cobalt chrome alloy. The titanium alloy may be one of: a Ti6AI4V grade 5 or grade 23 or another suitable grade of titanium alloy. The nickel alloy may be an Inconel TM alloy, for example an Inconel 718 or Inconel 625 alloy. Alternatively the nickel alloy may be a Hastelloy X. The copper alloy may be CuCrZr. The 3D printed housing 20 may be printed in layers and as such different layers may be made of different materials. In such a case, different regions of the 3D printed housing 20 can be made of different materials. For example, the body of the housing 20 may be made of a first material and the inside of the helical grooves 30 and or recirculation path 40 may be made of a second material. The second material may be a high hardness metal or ceramic for example, which, will reduce the wear on the housing 20 in use. Alternatively, the inside of the helical groove 30 may be made of a low friction polymer which reduces the friction on the ball bearing 4 in use. The 3D printed polymer or plastic may be any one of: PEEK, PEKK, PEI, ABS, PC, PLA or other material suitable for 3D printing. The composite material may be a combination of any of the previously provided materials. For example, the 3D printed housing 20 may be manufactured from a composite material made of a combination of metal and polymer or metal and ceramic or metal and any other material, or polymer and any other material, or ceramic and any other material. The present invention may be embodied in other specific forms without departing from the scope or spirit of the essential attributes thereof; therefore, the illustrated embodiment should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention. List of References: a Axis of Rotation 9     Angle D     Diameter of Ball Bearing L     Length Radius Axis of Movement Ballscrew Shaft Ball Bearing 100 Ballnut Housing Inner Surface Outer Surface Bore Helical Groove Start End Guiding Lip Outer Wall Recirculation Path Inner Wall Outer Wall Circuit First Transition Region Second Transition Region

Claims

1. A ballnut for a ballscrew having a ballscrew shaft, the ballnut comprising:a 3D printed housing with a radially inner surface for receiving a ballscrew shaft;the housing having at least one helical groove defined at least in part by the radially inner surface of the housing;the housing having at least one recirculation path;the at least one helical groove and at least one recirculation path are connected by a first transition region at a first end of the recirculation path and a first end of the at least one helical groove, and a second transition region at a second end of the recirculation path and a second end of the at least one helical groove;wherein the at least one helical groove, the at least one recirculation path and the first and second transition regions form a circuit for a rolling bearing to travel along when the ballnut is connected to a ballscrew shaft; andthe first and / or second transition region define a continuous path between the at least one helical groove and the at least one recirculation path.

2. The ballnut of claim 1, wherein the continuous path is a smooth path.

3. The ballnut of claim 1 or 2, wherein the continuous path is a non-steppedpath.

4. The ballnut of any preceding claim, wherein the continuous path is a substantially curved path in cross-section.

5. The ballnut of any preceding claim, wherein the housing is manufactured as a unitary component.

6. The ballnut of any preceding claim, wherein the ballnut does not comprise an insert forming a part of: the at least one recirculation path, or helical path, or circuit.

7. The ballnut of any preceding claim, wherein the at least one recirculationpath is contained within the housing.

8. The ballnut of any preceding claim, wherein a portion of the at least onerecirculation path is S-shaped.

9. The ballnut of any preceding claim wherein the helical groove comprises aguiding lip.

10. The ballnut of claim 9, wherein the guiding lip retains at least a portion ofthe rolling bearing.11.The ballnut of any of claims 1 to 10, wherein the ballnut has two circuits.The ballnut of any of claims1 to 10, wherein the ballnut has three circuits.The ballnut of any of claims1 to 10, wherein the ballnut has four circuits.

14. The ballnut of any of claims 1 to 10, wherein the ballnut has two to fourcircuits.15.The ballnut of any of claims1 to 10, wherein the ballnut has a plurality ofcircuits.

16. The ballnut of any one of claims 11 to 15, wherein the recirculation paths of each circuit are offset equally around the circumference of the radially inner surface of the housing in respect of each other.

17. The ballnut of any of claims 11 to 16, wherein the recirculation path of each circuit is offset by an azimuthal angle (0) in degrees of 9 = 360 / n, where n is the number of circuits, with respect of each other.

18. The ballnut of any preceding claim, wherein the radially inner surface is a through bore with a diameter of 2 mm to 20 mm.

19. The ballnut of any preceding claim, wherein the housing is 3D printed from one of: a metal, a plastic, a composite or a ceramic.

20. The ballnut of claim 19, wherein the metal is any one of: an aluminium ally, a steel, a stainless steel, a cobalt chrome alloy, a titanium alloy, a nickel alloy, copper, a copper alloy, a refractory metal, a precious metal, or precious metal alloy.

21. The ballnut of any preceding claim, wherein one or more of the: at least one helical groove, at least one recirculation path, first transition region and second transition region comprise: a "V" shaped wall or an approximately semicircular cross-section wall.

22. The ballnut of any preceding claim, wherein the rolling bearing is one of: a ball bearing and a roller bearing.

23. A ballscrew comprising a ballnut according to any of claims 1 to 22 and a ballscrew shaft.

24. A method of manufacturing a ballnut for a ballscrew having a ballscrew shaft, the method comprising the steps of:manufacturing a ballnut housing by 3D-printing, the housing having a radially inner surface for receiving a ballscrew shaft;the housing having at least one helical groove defined at least in part by the radially inner surface of the housing;the housing having at least one recirculation path;the at least one helical groove and at least one recirculation path are connected by a first transition region at a first end of the recirculation path and a first end of the at least one helical groove, and a second transition region at a second end of the recirculation path and a second end of the at least one helical groove;wherein the at least one helical groove, the at least one recirculation path and the first and second transition regions form a circuit for a rolling bearing to travel along when the ballnut is connected to a ballscrew shaft; andthe first and / or second transition region define a continuous path between the at least one helical groove and the at least one recirculation path.

25. The method of claim 24, wherein the housing is manufactured as a unitary component.

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