Apparatus and method for feeding arbitrarily thin wires with controlled tension

Abstract

A method for aligning a wire with a channel inlet includes directing a feed end of the wire toward a channel inlet of a feed channel and creating a pressure differential between the channel inlet and a channel outlet of the feed channel, thereby creating a pressure-driven gas flow around the wire toward the channel inlet. The wire is urged along the feed channel toward the channel outlet by shear forces of the gas flow created by the pressure differential. A method for preventing stiction of a wire against an inner wall of a narrow channel includes creating a pressure differential between the channel inlet and a channel outlet, thereby creating a pressure-driven gas flow around the feed end of the wire toward the channel inlet of the channel, and inducing one of fluttering or vibration in the wire at the feed end of the wire.

Description

[Technical Field]

[0001] Exemplary embodiments relate to techniques for delivering thin wires. [Background technology]

[0002] Thin wires are utilized in many technological applications, including manufacturing applications (e.g., welding, coating, and 3D printing) and medical procedures (e.g., minimally invasive surgery, stent placement, and deep brain stimulation), to name a few. In such applications, one end of a thin wire must be fed through a tube to a specific spatial location at a specific speed and / or angle. However, as the diameter of the wire being fed becomes arbitrarily small and approaches zero, the following unique properties inevitably arise, regardless of the material of construction:

[0003] Any thin wire will have reduced visibility, and may even become practically invisible to the human eye. The visibility of a thin wire can be approximately measured by how close its diameter is to the Abbe diffraction limit of visible light, which is on the order of 100 nm. There is a fundamental limit to the wire diameter below which the human eye can no longer distinguish the wire from its surroundings.

[0004] Any thin wire has a negligibly small bending stiffness proportional to EI / L, where E is the Young's modulus of the wire and I=πd 4 where / 64 is the moment of inertia of the wire when it is considered to have a circular cross section of diameter d, and L is the total length of the wire. Since the effect of wire diameter on bending stiffness is proportional to the fourth power, any thin wire that is initially straight and unsupported or unconstrained can bend to an unacceptably large extent under any small disturbance, including its own weight.

[0005] Any thin wire that is initially bent is difficult to straighten by plastic deformation because the minimum bend radius decreases in proportion to Ed / σ, where σ is the yield strength of the wire. An initial bend induced by residual stresses cannot be straightened by plastic deformation if the radius of curvature is greater than the minimum bend radius. As the wire diameter approaches zero, this minimum bend radius that cannot be straightened also approaches zero.

[0006] Any thin wire can buckle under negligible compressive force. 2 The compressive load required to buckle an arbitrarily thin wire, estimated by Euler's critical load for buckling, which is proportional to , drops off rapidly to a negligible magnitude as the diameter of the wire approaches zero. Summary of the Invention [Problem to be solved by the invention]

[0007] These characteristics inherent in any thin wire create challenges that are generally considered impossible to overcome simultaneously in order to enable the feeding of the wire through a thin tube. First, the reduced visibility, negligible bending stiffness, and non-straightenable minimum bend radius of any thin wire make initiating the feeding process difficult, as there is no reliable and convenient way to align the feeding end of any thin wire with the tube entrance before insertion.

[0008] Second, even if an arbitrarily thin wire is successfully inserted into a tube, van der Waals forces will cause stiction between the wire and the inner wall of the tube, resulting in a finite static friction force that must be overcome in order for the arbitrarily thin wire to advance further toward the tube exit. However, arbitrarily thin wires can buckle under negligibly small compressive forces proportional to the fourth power of the wire diameter, and will therefore buckle before the compressive load on the wire is large enough to overcome the static friction force proportional to the square of the wire diameter.

[0009] Furthermore, due to the negligible bending stiffness, minimum bend radius at which any thin wire cannot be straightened, and negligible critical buckling load, the only way to keep the wire straight during feeding is to maintain sufficient tension along the wire. This contradicts the goal of feeding a wire through a thin tube, which requires that the feeding end of any thin wire be free from any mechanical support. In other words, sufficient tension must be maintained on the wire without supporting the feeding end.

[0010] While a sufficiently thin wire may face one or more of the three challenges when being fed through a thin tube, successful feeding of any thin wire requires a method capable of overcoming all three challenges simultaneously. [Means for solving the problem]

[0011] In one embodiment, a method of aligning a wire with a channel inlet includes directing a feed end of the wire toward a channel inlet of a feed channel and creating a pressure differential between the channel inlet and a channel outlet of the feed channel to create a pressure-driven gas flow around the wire toward the channel inlet. The wire is urged along the feed channel toward the channel outlet by shear forces of the gas flow created by the pressure differential.

[0012] Additionally or alternatively, in this or other embodiments, one of fluttering or vibration is induced in the wire at the feed end of the wire. Additionally or alternatively, this or other embodiments prevent stiction of the wire against the inner walls of the delivery path by inducing fluttering.

[0013] Additionally or alternatively, in this or other embodiments, the channel inlet has a larger cross-sectional area than the channel outlet. Additionally or alternatively, in this or other embodiments, the wire is formed from a polymeric material.

[0014] Additionally or alternatively, in this or other embodiments, the wire has a wire diameter of less than 100 μm. Additionally or alternatively, in this or other embodiments, pressure-driven gas flow is directed from the channel inlet along the channel towards the channel outlet.

[0015] In another embodiment, a method for preventing sticking of a wire against an inner wall of a narrow passage includes creating a pressure differential between a passage inlet and a passage outlet of the passage, thereby creating a pressure-driven gas flow around a feed end of the wire to the passage inlet of the passage, and inducing one of fluttering or vibration in the wire at the feed end of the wire.

[0016] Additionally or alternatively, in this or other embodiments, the wire is urged along the pathway towards the pathway outlet by a pressure-driven gas flow generated by a pressure differential. Additionally or alternatively, in this or other embodiments, the channel inlet has a larger cross-sectional area than the channel outlet.

[0017] Additionally or alternatively, in this or other embodiments, the wire is formed from a polymeric material. Additionally or alternatively, in this or other embodiments, the wire has a wire diameter of less than 100 μm.

[0018] Additionally or alternatively, in this or other embodiments, pressure-driven gas flow is directed from the channel inlet along the channel towards the channel outlet. In yet another embodiment, a method for controlling tension in a wire directed along a pathway includes positioning a feed end of the wire inside the pathway and creating a pressure differential between a pathway inlet and a pathway outlet of the pathway, thereby creating a pressure-driven gas flow around the wire toward the pathway inlet of the pathway. The wire is urged along the pathway toward the pathway outlet by shear forces from the pressure-driven gas flow created by the pressure differential, and adjusting the pressure differential adjusts the tension in a portion of the wire between the pathway inlet and a discharge end of the wire opposite the feed end.

[0019] Additionally or alternatively, in this or other embodiments, one of fluttering or vibration is induced in the wire at the feed end of the wire. Additionally or alternatively, in this or other embodiments, stiction of the wire to the interior walls of the passage is prevented by inducing fluttering.

[0020] Additionally or alternatively, in this or other embodiments, the channel inlet has a larger cross-sectional area than the channel outlet. Additionally or alternatively, in this or other embodiments, the wire is formed from a polymeric material.

[0021] Additionally or alternatively, in this or other embodiments, the wire has a wire diameter of less than 100 μm. Additionally or alternatively, in this or other embodiments, pressure-driven gas flow is directed from the channel inlet along the channel towards the channel outlet.

[0022] The following description should not be considered limiting in any way. Referring to the accompanying drawings, in which like elements are numbered alike, the drawings show: [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 10 is a schematic diagram of the feeding of a wire along a guide tube. [Figure 2] FIG. 1 is a diagram of an experimental setup for measuring wire tension. [Figure 3] FIG. 10 is a diagram of a wire entering a guide tube without pressurized gas flow. [Figure 4] FIG. 10 is a diagram of a wire entering a guide tube with a pressurized gas flow. [Figure 5] 13A-13C illustrate the elimination of stiction of the wire against the inner wall of the guide tube. [Figure 6] FIG. 10 is a diagram of stiction of the wire against the inner wall of the guide tube. [Figure 7] FIG. 10 is a diagram of a hanging wire within a guide tube. [Figure 8] FIG. 10 is a diagram of a tensioned wire within a guide tube. DETAILED DESCRIPTION OF THE INVENTION

[0024] A detailed description of one or more embodiments of the disclosed apparatus and method is presented herein by way of example, and not limitation, with reference to the drawings. The present disclosure describes methods and apparatus that allow for the use of a thin feed path as a mechanical guide through which any thin wire is pulled and / or dragged from one end of the feed path to the other end of the feed path primarily, if not solely, by shear forces exerted on the wire by pressure-driven gas flow within the feed path, as shown in Figure 1.

[0025] The wire 10 is fed into a feed path, in the illustrated embodiment, a feed tube 12, in a feed direction 14 at a tube inlet 16 at a first end of the feed tube 12 and urged toward a tube outlet 18 at a second end of the feed tube 12. In some embodiments, the wire 10 is formed from a polymer, while in other embodiments, the wire 10 is formed from a metallic material. The feed tube 12 acts as a mechanical guide to direct the wire 10 toward a selected location at the tube outlet 18. The feed tube 12 includes a tube body 20 disposed between the tube inlet 16 and the tube outlet 18. In some embodiments, the tube body 20 has an inner diameter 22 that is smaller than a cross-sectional area or inlet diameter 24 of the tube inlet 16. A pressure-driven gas flow 26 is forced into the tube inlet 16 from a gas source 28 maintained at a pressure greater than the gas pressure at the tube outlet 18.

[0026] 2, this gas source 28 may be obtained by placing the tube inlet 16 and wire 10 in a pressure chamber and the tube outlet 18 in open air. In other embodiments, the gas source 28 may be obtained by placing the tube inlet 16 and wire 10 in open air and the tube outlet 18 in a vacuum chamber 50. The pressure-driven gas flow 26 acts on the wire 10, and the shear force of the pressure-driven gas flow 26 acting on the wire 10 guides the wire 10 into the tube inlet 16, pushes or pulls the wire 10 through the tube body 20 and into the tube outlet 18.

[0027] The velocity of the wire 10 discharged at the discharge end 38 of the wire 10 governs the target feed velocity of the wire 10 at the feed end 30 or tip of the wire 10, the objective being to maintain / control wire tension at the discharge end 28 while ensuring that the actual wire velocity of the wire 10 at the feed end 30 accurately tracks the target feed velocity set at the discharge end 38. Generally, feeding a wire through a tube does not necessarily require control of wire tension. However, for any thin wire 10, the feeding method will fail without a mechanism for maintaining sufficient wire tension due to the challenges discussed above. In some embodiments, the wire 10 has a thickness of less than 100 μm, and in other embodiments, the wire 10 has a thickness of less than 10 μm. The key to achieving a target feed rate while maintaining tension in the wire 10 is the dynamic behavior of the thin wire interacting with the pressure-driven gas flow 26 within the feed tube 12, which can be utilized to overcome the aforementioned challenges to achieve the goal of feeding the wire 10 through the feed tube 12 with controlled tension, more specifically, through flow-induced alignment, vibration, and tension.

[0028] The feeding process begins with inserting the feeding end 30 of the wire 10 into the tube inlet 16, which has an enlarged cross-sectional area relative to the tube body 20, as shown in FIG. 3. Referring to FIG. 4, when the pressure-driven gas flow 26 is activated, the pressure-driven gas flow 26 aligns the feeding end 30 of the wire 10 with the body opening 32 of the tube body 20. More specifically, the pressure-driven gas flow 26 is induced by a pressure differential between the tube inlet 16 and the tube outlet 18, such that the gas pressure at the tube inlet 16 is maintained higher than the gas pressure at the tube outlet 18, resulting in the gas flow 26 surrounding the tube inlet 16 flowing within the tube toward the tube outlet 18. In some embodiments, the tube inlet 16 has a diameter ranging from 1 to 10 times the diameter of the wire 10. Furthermore, in some embodiments, the tube inlet 16 is enlarged relative to the tube body 20, while in other embodiments, the tube body 20 has a diameter equal to the diameter of the tube inlet 16.

[0029] The expanded tube inlet 16 relative to the tube body 20 creates a converging flow pattern under the appropriate conditions, as shown in FIG. 4 . When a sufficiently thin (and therefore lightweight and flexible) wire 10's feed end 30 is brought close to the tube inlet 16, it is pulled toward the tube inlet 30 and self-aligns with the streamlines of the converging gas stream 26, automatically entering the feed tube 12 and body opening 32 as more wire is discharged from the discharge end 38. Depending on the amount of pressure differential imparted to the gas stream 26, the dimensions of the feed tube 12, and the dimensions and properties of the wire 10, the feed end 30 of the wire 10 may or may not sway under the gas stream 26 as it is aligned and fed into the tube inlet 16. Note that how the feed wire 10 is discharged or delivered at the discharge end 38 should not be used to limit the scope of this disclosure.

[0030] After the feed end 30 of the wire 10 enters the feed tube 12 under the pressure-driven gas flow 26, the pressure difference between the tube inlet 16 and the tube outlet 18 may need to be adjusted so that the feed end 30 of the wire 10 begins to vibrate or continues to vibrate as the shear force exerted by the gas flow 26 on the surface of the feed wire 10 pulls the feed end 30 of the wire 10 further into the feed tube 12, as shown in Figure 5. The vibration / fluttering of the feed end 30 of the wire 10 prevents the wire 10 from adhering to the inner wall 36 of the feed tube 12 under intermolecular attractive forces, such as van der Waals forces, as shown in Figure 6.

[0031] While the feed end 30 of the wire 10 is still inside the feed tube 12 and fluttering, the pressure differential between the tube inlet 16 and the tube outlet 18 may still need to be adjusted so that the total shear force exerted by the pressure-driven gas flow 26 on the surface of the wire 10 inside the feed tube 12 generates a sufficient pulling / drag force so that there is sufficient tension in the portion of the wire 10 outside the feed tube 12 between the tube inlet 16 and the discharge end 28 to keep the wire 10 straight.

[0032] By utilizing flow-induced alignment, vibration, and tension, wire 10 can be successfully fed through feed tube 12 at a selected and controlled rate and tension with proper design of the dimensions and operating pressure of feed tube 12. In some embodiments, the pressure differential is less than about 15 psi.

[0033] Referring to FIG. 7, when gas flow 26 is not activated, tension on the wire is not maintained and wire 10 may be prone to sagging, but when gas flow 26 is activated, tension on wire 10 is maintained to properly feed wire 10 through guide tube 12, as shown in FIG.

[0034] Referring again to FIG. 2 , an experimental setup 52 is shown for measuring the tension in the wire 10 between the tube inlet 16 and the wire's discharge end 38 while feeding the wire 10 through the feed tube 12. A pressure difference between the tube inlet 16 and the tube outlet 18 is established using a vacuum system connected to the tube outlet 18, while the tube inlet 16 is exposed to the atmosphere at atmospheric pressure. The vacuum system consists of a vacuum pump 54 as an energy source, a variable throttle valve 56 for controlling the gas flow rate and / or pressure, a flow meter 58 for measuring the gas flow rate, and a pressure meter 60 for measuring the gauge pressure of the gas at the tube outlet 18. A vacuum hose 62 is used to airtightly connect all components of the vacuum system so that all gas exiting the tube outlet 18 is vented to the atmosphere by the vacuum pump 54 without leakage. Note that another way to create such a pressure difference is to connect the tube inlet 16 to a pressure vessel and expose the tube outlet 18 to the atmosphere at atmospheric pressure. Alternatively, such a pressure differential can be created by connecting the tube inlet 16 to a pressure vessel while simultaneously connecting the tube outlet 18 to a vacuum system. It should further be noted that it is the difference between the values ​​of the gas pressure at the tube inlet 16 and the tube outlet 18 that is important, not the actual values ​​of the gas pressure at the tube inlet 16 and the tube outlet 18.

[0035] A polymer wire 10 having a diameter of 90 mm to 100 mm discharged from a payoff spool 64 is fed one at a time through several feed tubes 12 having different inner diameters, while the tension in the wire section between the tube exit 18 of the feed tube 12 and the discharge end 38 of the wire is measured using an analytical balance 66.

[0036] The analytical balance 66 reading is first zeroed with the fixed roller 68 positioned above it without the wire. The fixed roller 68 has a weight much greater than the magnitude of the flow-induced tension being measured, but much less rotational friction. To measure the wire tension, two additional frictionless fixed rollers 70 are positioned above the roller 68 on the analytical balance. Next, the thin wire 10 is wrapped around all three fixed rollers 68, 70 as shown as it is fed through the feed tube 12. Care is taken to ensure that the section of wire on the analytical balance 66 between the fixed rollers 68, 70 is vertical and that the measurement is taken when the wire's feed / front end has just reached the tube exit 18. Therefore, the tension in the wire section 72 between the tube exit 18 and the wire's discharge end 38 is measured as half the absolute value of the reading shown on the analytical balance 66. Table 1 shows a tabulated plot of experimental tension data for different tube inner diameters, tube lengths, gas pressures, and flow rates. As is evident from this data, the tension in the wire can be controlled by varying the pressure differential and the dimensions of the tube.

[0037] [Table 1]

[0038] The term "about" is intended to include the degree of error associated with measurement of the particular quantity based on equipment available at the time of filing this application. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. It will be further understood that, as used herein, the terms "comprises" and / or "comprising" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0039] While the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope of the present disclosure. Therefore, the present disclosure is not limited to the particular embodiment disclosed as the best mode contemplated for carrying out the disclosure, but the present disclosure is intended to include all embodiments falling within the scope of the appended claims.

Claims

1. 1. A method for aligning a wire with a channel entrance, comprising: directing a feed end of the wire toward a channel entrance of the feed channel; creating a pressure differential between the channel inlet and the channel outlet of the delivery channel, thereby creating a pressure-driven gas flow around the wire and into the channel inlet; and urging the wire along the feed path toward the path outlet by a shear force of the gas flow created by the pressure differential.

2. The method of claim 1 further comprising inducing one of fluttering or vibration in the wire at the feed end of the wire.

3. The method of claim 2 , further comprising preventing stiction of the wire against an inner wall of the feed path by inducing fluttering.

4. The method of claim 1 , wherein the channel inlet has a larger cross-sectional area than the channel outlet.

5. The method of claim 1 , wherein the wire is formed from a polymeric material.

6. The method of claim 1 , wherein the wire has a wire diameter of less than 100 μm.

7. The method of claim 1 , wherein the pressure-driven gas flow is directed from the channel inlet along the channel toward the channel outlet.

8. 1. A method for preventing stiction of a wire against an inner wall of a narrow passage, comprising: creating a pressure differential between a channel inlet and a channel outlet of the channel, thereby creating a pressure-driven gas flow around the feed end of the wire into the channel inlet; and inducing one of fluttering or vibration in the wire at the feed end of the wire.

9. The method of claim 8 , further comprising urging the wire along the path toward the path outlet with the pressure-driven gas flow created by the pressure differential.

10. The method of claim 8 , wherein the channel inlet has a larger cross-sectional area than the channel outlet.

11. The method of claim 8 , wherein the wire is formed from a polymeric material.

12. The method of claim 8 , wherein the wire has a wire diameter of less than 100 μm.

13. The method of claim 8 , wherein the pressure-driven gas flow is directed from the channel inlet along the channel toward the channel outlet.

14. 1. A method of controlling tension in a wire directed along a path, comprising: positioning a feed end of the wire inside the channel; creating a pressure differential between a channel inlet and a channel outlet of the channel, thereby creating a pressure-driven gas flow around the wire and into the channel inlet of the channel; urging the wire along the path toward the path outlet by shear forces from the pressure-driven gas flow generated by the pressure differential; and adjusting the pressure differential to adjust tension in a portion of the wire between the channel inlet and a discharge end of the wire opposite the feed end.

15. The method of claim 14 further comprising inducing one of fluttering or vibration in the wire at the feed end of the wire.

16. 16. The method of claim 15, wherein inducing fluttering prevents stiction of wires to the interior walls of the passageway.

17. The method of claim 14 , wherein the channel inlet has a larger cross-sectional area than the channel outlet.

18. The method of claim 14 , wherein the wire is formed from a polymeric material.

19. The method of claim 14, wherein the wire has a wire diameter of less than 100 μm.

20. The method of claim 14 , wherein the pressure-driven gas flow is directed from the channel inlet along the channel toward the channel outlet.

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