FIELD OF THE INVENTION

The present invention relates to a polishing instrument, in particular a polishing instrument having a shaft comprising a tapered neck and a tip preferably having a radius or equivalent radius of less than 3cm, suitable for polishing inter alia high aspect ratio profiles but the invention is not limited thereto, and a method of manufacturing thereof.

BACKGROUND OF THE INVENTION

In polishing, the tool plays a significant role in the process of removing material. The material, geometry, and dimensions of the tool are important factors that limit or enable the shapes and sizes of elements to be polished by a particular tool. There is an increasing need for polishing tools suitable for polishing small- dimension parts or elements and/or high aspect ratio profile elements, such as optical components for lasers and imaging.

Polishing may be characterised as a process in which the shape of a workpiece is maintained while its surface is smoothed. This is typically obtained by moving the polishing tool in a pattern that follows (resembling) the shape of the workpiece which is different from a shaping process based on material removal in which the work tool is moved in a pattern providing a variation of the geometry of the workpiece.

The variety of currently available micro-polishing tools is limited, largely due to inefficient methods of manufacturing, such as gluing the tip to the shaft. In addition to increasing manufacturing costs, such methods limit the possible geometries of the tool, and obviate the possibility of complex structural shapes that would be ideal for polishing high aspect ratio profiles. For example, gluing limits the strength of the connection between the tip and the shaft and may require a large surface area of the tip to be in contact with the shaft. Furthermore, most current methods of manufacturing are limited to a single polishing tool structure, and more flexibility is needed to efficiently produce tools having different shapes or materials, especially for the polishing tip. Likewise, a tool structure is needed that is compatible with this flexibility. In addition current manufacturing methods for polishing tools do not satisfy requirements of high geometrical accuracy relevant for high precision polishing applications.

A particular branch of polishing is ultraprecision polishing of miniature components and features with small curvature radii is limited by surface accessibility, availability of suitable tools and the capability to control material removal with sufficient spatial resolution.

Micro polishing consists in the downscaling of mechanical polishing using compliant micro tools. Owing to the small tool size, micro polishing is

characterized by a reduced contact area, enabling control of the local material removal with a high spatial resolution. Furthermore, long tools with small dimensions and sub millimeter curvature radius guarantee access to high aspect ratio cavities and high curvature surface features.

Material removal rate in polishing is controlled through the variables influencing the conditions at the tool-workpiece interface, namely the size and shape of the contact area, the distribution and velocity field of the abrasive particles, and the contact pressure distribution on the contact surface.

Ultraprecision corrective polishing is used in manufacturing of optical components such as moulds for glass moulding of glass lenses, screens, etc. In such use, polishing is used not only to obtain a very fine surface topography (in the order of Sa 1 nm), but also to correct residual form errors from the previous

manufacturing process steps. Thus, prior to polishing, a measurement of the surface geometry is carried out and, by subtracting the nominal surface geometry, the excess material distribution on the surface is revealed (typically in the order of 1 pm). Corrective polishing consists in generating tool paths to polish the surface where the variables governing the material removal rate (MRR), essentially time and contact pressure, are modulated to match the local amount of material to be removed. In this way, areas with higher residual material are either polished for longer time (feed modulation) or with higher pressure (force moderation). US 2002/0016139 relates to a polishing tool and its manufacturing method, and relates in particular to the structure of a fixed-abrasive polishing tool or a polishing pad. The tool is described as being used for CMP (chemical mechanical polishing). Typical CMP tools consist of a rotating and extremely flat plate which is covered by a pad. Because the fixed-abrasive polishing tool lacks sufficient strength so that, if it is unsupported, transporting and attaching to a machine may cause to break or damaged, and therefore, it is fixed to a holder base. Also, because the fixed-abrasive polishing tool is a flat shaped tool, and also, the structural form and the material are vulnerable to distortion and volume expansion due to moisture absorption, the fixed-abrasive polishing tool must be sufficiently wetted during any fabrication process so that the water content within the tool does not become unbalanced.

US2015/0283668 relates to a generally annular retaining ring assembly, also for chemical mechanical polishing (CMP), having a retaining ring and a backing ring. The ring assembly is flat and unsuitable for polishing high aspect ratio profiles.

The article entitled "Development of Ultrasonic Vibration Assisted Polishing Machine for Micro Aspheric Die and Mold" by Suzuki et al, Annals of the CIRP Vol. 55/1/2006 relates to an ultrasonic vibration assisted polishing machine for finishing micro aspheric dies and molds with a diameter less than 3mm. However, the polishing tool disclosed has has limited ability to efficiently polish small- dimension parts or elements and/or high aspect ratio profiles. Generally, such micro-polishing tools are formed by gluing the tip to the top of the shaft.

GB790003A relates to the manufacture of grinding and polishing members bound with synthetic material and having a compressed abrasive grain skeleton. The method comprises arranging abrasive grains in a mould provided with a nozzle or nozzles and air-escape ducts, and of shape corresponding to the desired shape of the tool, compacting the grains by vibration, and subjecting them to pressure to form a rigid skeleton. However, such a method may result in uneven dispersion of the abrasive grains, and the tool surface may require shaping such that the polishing tool may not be ready to use immediately after removal from the mold. Hence, an improved polishing tool and method of manufacturing a polishing tool would be advantageous, and in particular a polishing tool more suitable for polishing high aspect ratio profiles would be advantageous.

OBJECT OF THE INVENTION

It is a further object of the present invention to provide an alternative to the prior art.

In particular, it may be seen as an object of the present invention to provide a polishing tool that solves the above mentioned problems of the prior art with difficulty reaching surfaces having high degree of curvature and with lack of flexibility. It is desired to have a polishing tool with a geometry, dimensions, materials, and compression set suitable for polishing high aspect ratio surfaces. It is further desired to provide a method of manufacturing such a tool with efficiency and flexibility in producing different types of polishing tools for different functions. Further, it is desired to provide a polishing tool and method of polishing, such as micro-polishing, an object by use of the polishing tool that allow for minimal runout.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a polishing instrument, the polishing instrument comprising:

an elongated shaft comprising a neck, the neck being tapered towards a first end of said elongated shaft;

a tip having a shape, such as a curved shape, configured to perform polishing at the first end of said elongated shaft, the tip being formed of at least one thermoplastic and/or thermosetting material and having a radius or equivalent radius of less than 3cm, such as less than 10cm.

It is found that many embodiments of the invention are suitable for polishing in general without size limitations. Accordingly, the scope of the claims is not as such limited to e.g. micro polishing. In some preferred embodiments, the elongated shaft may be made of a first thermoplastic and/or thermosetting polymer material and the tip may be made of a second thermoplastic and/or thermosetting polymer material, being a different polymer material than the first polymer material. In such cases, it may be preferred that the elasticity modulus of the second polymer material is lower than the elasticity modulus of the first polymer material.

In some preferred embodiments, the polishing instruments has a compression set larger than 10% and less than 50% such that it is configured to be used with rotational and/or vibrational motion in contact with an element. The compression set may preferably be determined according to ISO standard 815. In some preferred embodiment, the shaft may be made from a different material. In some preferred embodiments, the polishing instrument and/or in particular the tip has a compression set larger than 10% and less than 50% such that it is configured to be used with rotational and/or vibrational motion in contact with an element.

As presented herein, the compression set may preferably be determined according to ISO standard 815. Compression set is often part of a characterization of a material and can be found in many data sheets or the like for materials.

In preferred embodiments, the tip may have a radius of curvature of less than 500pm. In other embodiments, the tip has a radius of curvature less the 10 cm.

In preferred embodiments, polishing instrument and/or in particular the tip has a compression set less than 40%.

If the footprint is desired to be increased it may be an advantage to have a compression set larger than 10%. However, alternatively the compression set can be as low as possible, preferably as close to 0 as the choice of materials allows, to achieve complete shape memory.

In preferred embodiments where only the tip is formed formed of at least one thermoplastic and/or thermosetting material with the otherwise specified features herein, the shaft may be made from other material(s). The term "equivalent radius", as used throughout the description and as claimed, is understood to be the perimeter of any cross sectional area of the tip divided by 2 times pi (i.e. perimeter/2*pi). The equivalent radius may be less than 3cm at one location along the longitudinal length of the tip, at multiple locations, or along the entire longitudinal length of the tip. For example, for a sphere shape, the equivalent radius is the radius of the sphere and for a cylindrical shape, the equivalent radius is the radius of the cylinder.

In preferred embodiments, the tip preferably being formed of at least one thermoplastic and/or thermosetting material and having a radius or equivalent radius of less than 10.0 cm, such as less than 5.0 cm, preferably less than 2.5 cm, such as less than 2.0 cm, preferably less than 1.5 cm, such as less than 1.0 cm, such as less than 0.5 cm.

In preferred embodiments according to the present invention, the tip being preferably formed of at least one thermoplastic and/or thermosetting material and having a radius or equivalent radius of less 30 times, such as less than 20 time, preferably less than 15 times the radius or equivalent radius of the first end of the elongated shaft. It is preferred that for larger polishing tool, the shaft may have a smaller diameter than the tip.

A lower limit for the radius or equivalent radius is in some preferred embodiments (combinable with the otherwise disclosed upper limits) at least twice as large as the radius or equivalent radius of the first end of the elongated shaft.

According to alternative embodiments of the present invention, the polishing instrument comprises a tip having a prismatic shape, such as a cube or hexagonal prism, configured to perform polishing at the first end of said elongated shaft. Such prismatic shapes are especially advantageous for vibrational polishing.

The term "tapered" when describing the neck of the shaft is understood to mean that the neck is a longitudinal section of progressively decreasing diameter towards a first end of said elongated shaft. The at least one thermoplastic and/or thermosetting material may be a polymer compound of thermoplastic and/or thermosetting materials.

The tip of the polishing instrument preferably has a radius of curvature of less than 500pm and one or more circular cross sections. The tip may be spherical or cylindrical.

At least one of said one or more circular cross sections of the tip preferably has a diameter greater than the diameter of the first end of the elongated shaft, such as at least twice as large as the diameter of the first end of the elongated shaft.

When the tip is cylindrical, many circular cross sections of the tip may have a diameter greater than the diameter of the first end of the elongated shaft.

The elongated shaft preferably has its smallest dimension less than 5 mm, such as less than 2.5 mm, preferably less than 1 mm, such as less 500pm, and the tip preferably has its largest dimension less than 10 cm, such as less than 15 mm, preferably less than 10 mm, such as less than 5 mm, preferably less than 1 mm. The length of the polishing instrument is preferably less than 100 mm, such as less than 75 mm, preferably less than 40 mm, such as less than 3mm, and may be less than 2mm. The neck is tapered, and the length of the neck is preferably at least one quarter of the length of the polishing instrument, and the length of the neck may be one third or one half of the length of the polishing instrument, to allow for better accessibility to high aspect ratio profiles.

In preferred embodiments, the at least one thermoplastic and/or thermosetting material may comprise a thermoplastic elastomer.

The polishing instrument may be formed entirely of a single material that may be a polymer compound of thermoplastic and/or thermosetting materials. At least the tip is preferably formed at least of thermoplastic elastomer (TPE) material. The thermoplastic elastomer may comprise thermoplastic polyurethane (TPU).

The polishing instrument preferably has a compression set of less than 50%, such as less that 40% or even less that 30%. The compression set may preferably be determined according to ISO standad 815. In preferred embodiments, the tip may have a stabilization time less than 100.0 seconds such as less than 75.0 seconds, preferably less than 50.0 seconds, such as less than 25.0 seconds, preferably less than 15.0 seconds and preferably larger than 0.25 seconds.

Stabilization time as used herein is typically used for referencing the time necessary to reach contact pressure stabilization, and may be used in

characterizing relaxation. If the stabilization time is small, the contact pressure reduction takes place substantially immediately after the application of offset, and therefore does not influence the material removal rate during polishing.

Stabilization time may preferably be determined based on experiment, during which contact pressure is measured. As presented in fig. 8 herein, the force stabilizes and the stabilization time may be defined as the time duration until a steady state is reached. Steady state may preferably be considered to have been reached when the contact pressure varies with +-15%, such as +- 10%, preferably +-5% around a mean value.

In preferred embodiments the tip may be porous, preferably having an average pore size in the order of 3-5 microns.

In preferred embodiments, the tip or the polishing instrument (1) may be made from a material, or one or more materials, selected from the group consisting of polycarbonate (PC), polymethylmethylacrilate (PMMA), polyether ether ketone (PEEK), polystyrene (PS), cellulose acetate (CA), polyethylene terephthalate (PET), polyoxymethlyne (POM), polypropylene (PP), nylon (PA), polyethylene (PE), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polylactic acid (PLA), thermoplastic elastomer (TPE), high density polyethylene (HDPE), epoxy, polyurethane elastomer (PU), Bakelite (phenolic), polyester thermoset (PE), butyl rubber (HR), ethylene-vinyl acetate), acrylonitrile butadiene styrene (ABS), thermoplastic polyurethane (TPU).

In preferred embodiments, the tip may have one or more circular cross sections.

In such embodiments, at least one of the one or more circular cross sections of the tip may have a diameter at least twice as large as the diameter of the first end of the elongated shaft. Alternatively, the elongated shaft may further comprise an inner core, the inner core extending from a second end of said elongated shaft and along the majority of the length of said elongated shaft through at least a part of said neck. The inner core may be formed of a different material than the material surrounding the inner core, and may have a strength greater than the strength of the material surrounding said inner core.

According to either of these embodiments, the tip and said elongated shaft may be connected via a mechanical interlocking, which may be achieved by at least one of:

a. at least one undercut in the elongated shaft;

b. a rod shaped or T-shaped locking element extending from the first end of the elongated shaft configured to fit inside the tip;

c. at least one cross hole in the shaft;

d. surface texturing of the elongated shaft configured to allow the tip to adhere to the elongated shaft;

e. interlocking threads on the elongated shaft; and

f. the tip having a shape configured to increase the contact area and consequently the adhesion force between the tip and the elongated shaft.

Alternatively or additionally, the tip and the elongated shaft may be connected via chemical interlocking due to material compatibility.

The tip and the elongated shaft may be removably connected.

In preferred embodiments, the polishing instrument may be formed entirely of a single thermoplastic and/or thermosetting material.

The tip may have a uniform thickness and/or may further comprise an outer coating.

Preferably, the elongated shaft has a cylindricity of less than 2pm. The elongated shaft may be cylindrical and the tapered neck may be conical.

The above described object and several other objects are intended to be obtained in a second aspect of the invention by providing a method of, polishing such as micro-polishing an object by use of the polishing instrument according to the first aspect, the method comprising applying a force to the polishing instrument 1. The method preferably comprises applying a rotational speed while applying said force to the polishing instrument 1 of at least 100, such as at least 2.000 rpm while preferably maintaining a runout of the polishing instrument 1 less than lOpm.

In some preferred embodiments, the method of polishing, such as micro-polishing may further comprise pre-paring the polishing tool for polishing prior to polishing an object by applying a force to the polishing instrument while applying a rotational speed to the polishing instrument of at least 100 rpm, such as at least 500 rpm, such as at least 2.000 rpm for a time period substantial equal to or larger than the stabilization time of the tip, such as for at least at least 5 seconds, preferably for at least 10 seconds, such as for at least 15 seconds, such as for at least 20 seconds, and preferably less than 100 seconds, such as less than 50 seconds, preferably less than 25 seconds.

In some preferred embodiments, the method of polishing, such as micro-polishing may further comprise

prior to polishing measuring the surface geometry of the object, determining excess material distribution by subtracting the nominal surface geometry from the measured surface geometry,

while polishing, moving the tip along the surface of the object with the tip being arranged relatively to the surface of the object to remove the excess material while applying a rotational speed to the polishing instrument of at least 100 rpm, such as at least 2.000 rpm.

In some preferred embodiments, the method of polishing, such as micro-polishing may be carried out by feed modulation according to which the speed of the tip along the object may be varied depending on the amount of material to be removed, preferably so that the larger amount of material to be removed the lower the speed of the tip along object is.

In some preferred embodiments, the method of polishing, such as micro-polishing may be carried out by force modulation according to which the contact force between object and tip may be varied depending on the amount of material to be removed, preferably so that the larger amount of material to be removed, the larger the contact force

In some preferred embodiments, the method of polishing, such as micro-polishing may further comprise feeding a fluid including abrasives, such as silicon carbide, aluminum oxide, boron carbide, cerium oxide, zirconium oxide, cubic boron nitride, diamond, as well as their combinations, the abrasive preferably has a particle size with mean below 20 pm, such as between 15 pm and 0.01 pm, onto the surface of the object being polishing while being polished.

In some preferred embodiments, the fluid including abrasive is water based, ethanol based, oil based, glycerol based or have other bases and wherein the concentration of the abrasives concentration is preferably in the range of 0.0001 wt% to 5wt%

The above described object and several other objects are intended to be obtained in a third aspect of the invention by providing a method for forming a polishing instrument according to the first aspect of the invention using injection moulding. The method comprises providing a mold shaped to form the tip of the polishing instrument and injecting at least one thermoplastic and/or thermosetting material into the mold to form the tip onto an existing shaft and/or onto an existing tip of the polishing instrument. The method may further comprise, prior to injection of the at least one thermoplastic and/or thermosetting material into the mold, the steps of a) heating and mixing a desired proportion in weight of micro-abrasive grains relative to the weight of the at least one thermoplastic and/or

thermosetting material into the at least one thermoplastic and/or thermosetting material, and b) compounding the at least one thermoplastic and/or

thermosetting material comprising said micro-abrasive grains to achieve a desired dispersion and homogeneity. Such compounding of grains may be performed with a twin extruder. The polishing instrument with the newly formed tip may be configured to be used with rotational and/or vibrational motion in contact with an element immediately after removal from the mold.

Alternatively, a method for forming a polishing instrument using injection molding is disclosed according to the present invention. The method comprises providing a mold shaped to form an entire polishing instrument comprising a tip and a shaft, and injecting at least one thermoplastic and/or thermosetting material into the mold to form the entire polishing instrument comprising a tip and a shaft. The method may further comprise, prior to injection of the at least one thermoplastic and/or thermosetting material into the mold, the steps of a) heating and mixing a desired proportion in weight of micro-abrasive grains relative to the weight of the at least one thermoplastic and/or thermosetting material into the at least one thermoplastic and/or thermosetting material, and b) compounding the at least one thermoplastic and/or thermosetting material comprising said micro-abrasive grains to achieve a desired dispersion and homogeneity. Such compounding of grains may be performed with a twin extruder. The polishing instrument may be configured to be used with rotational and/or vibrational motion in contact with an element immediately after removal from the mold. The above described object and several other objects are intended to be obtained in a fourth aspect of the invention by providing a method for forming a polishing instrument using injection moulding, comprising :

i) providing a mold shaped to form at least the tip of a polishing

instrument comprising an elongated shaft and a tip at a first end of said elongated shaft, said tip having preferably having a radius or equivalent radius of less than 3cm and shape, such as a curved shape, configured to perform polishing, said elongated shaft comprising a neck, said neck being tapered towards said first end of said elongated shaft;

ii) compounding thermoplastic and/or thermosetting materials to form a polymer compound material;

iii) subsequently injecting said compound material into said mold to form at least said tip, thereby providing said polishing instrument as a unified body comprising said tip and said elongated shaft;

iv) removing at least said tip of said polishing instrument from said

mold such that said polishing instrument is removed from said mold.

If the footprint is desired to be increased it may be an advantage to have a compression set larger than 10 %. However, alternatively the compression set can be as low as possible, preferably as close to 0 as the choice of materials allows, to achieve complete shape memory.

In some preferred embodiments, said polishing instrument may have a

compression set larger than 10% and less than 50% such that said polishing instrument is configured to be used with rotational and/or vibrational motion in contact with an element immediately after removal from the mold.

The compression set may preferably be determined according to ISO standard 815.

If the footprint is desired to be increased it may be an advantage to have a compression set larger than 10%. However, alternatively the compression set can be as low as possible, preferably as close to 0 as the choice of materials allows, to achieve complete shape memory.

Step iii) of the method preferably comprises subsequently injecting said compound material into said mold to form only said tip onto a pre-existing shaft and/or pre-existing tip of said polishing instrument.

According to a preferred embodiment of the invention, step i) further comprises providing a mold configured to form a tip having its largest dimension less than lmm, a radius of curvature less than 500pm and at least one circular cross section. In other preferred embodiments, the tip may have a radius (R) or equivalent radius of less than 3cm, preferably less than 10cm. At least one of the circular cross sections may have a diameter at least twice as large as the diameter of the first end of the elongated shaft or the diameter of the portion of the mold related to the first end of the elongated shaft. When the mold is configured to form at least part of the shaft of a polishing instrument, the mold is preferably configured to form an elongated shaft having its smallest dimension less than 500pm. When the mold is configured to form an entire polishing instrument, the mold is preferably configured to form a polishing instrument having a length smaller than 3mm. The mold may have dimensions and geometry to form a polishing instrument having a length smaller than 2mm. The compression set of the polishing instrument formed by the method is preferably less than 50%, such as less that 40% or even less that 30%. The compression set may preferably be determined according to ISO standard 815.

The method may further comprise spin coating said tip to achieve an optimal thickness distribution.

The method preferably further comprises the steps of:

a) heating and mixing a desired proportion in weight of micro-abrasive grains relative to the weight of said polymer compound material into said polymer compound material, and

b) compounding said polymer compound material comprising said micro-abrasive grains to achieve a desired dispersion and homogeneity,

said steps a) and b) being performed prior to said injection of said compound material into said mold. Such compounding of the polymer compound material with micro-abrasive grains may be performed with a twin extruder.

The micro-abrasive grains may be alumina or diamond. The desired proportion in weight of micro-abrasive grains relative to the weight of said polymer compound material is preferably between 0.3% and 0.5%.

The method may further comprise compounding said polymer compound material with soluble particles and subsequently dissolving them to achieve a desired porosity of the polishing instrument.

In some preferred embodiments, the method for forming a polishing instrument using injection moulding, step i) above may comprise providing a mold shaped to form at least the tip of a polishing instrument, wherein said tip may have a radius of curvature as disclosed herein, such as less than 500pm.

In some preferred embodiments, the method for forming a polishing instrument using injection moulding, step i) above may comprise providing a mold shaped to form at least the tip of a polishing instrument, wherein said tip may have cross section(s) as disclosed herein, such as at least one circular cross section. In some preferred embodiments, the method for forming a polishing instrument using injection, step iii) above may comprise subsequently injecting said compound material into said mold to form only said tip onto a pre-existing shaft and/or pre-existing tip of said polishing instrument.

The individual aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from the following description with reference to the described embodiments.

BRIEF DESCRIPTION OF THE FIGURES

The polishing tool according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of

implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

Figure 1 shows a schematic drawing of an exemplary polishing instrument according to the present invention, having a spherically shaped tip.

Figure 2 shows a schematic drawing of an alternative exemplary polishing instrument according to the present invention, having an inner core within the shaft, and a cylindrically shaped tip.

Figures 3A -3B show schematic drawings of alternative exemplary polishing instrument according to the present invention, wherein the shaft has a locking element for mechanical interlocking with the tip.

Figures 4A-4C show schematic drawings of alternative exemplary polishing instruments according to the present invention, wherein the shaft has structural features configured to allow mechanical interlocking with the tip.

Figure 5 shows a schematic drawing of an alternative exemplary polishing instrument according to the present invention, having a tip overmolded over an existing polishing tool. Figure 6 shows a schematic drawing of the exemplary polishing instrument according to any of the previous embodiments, wherein the tip has an outer coating.

Figure 7 shows a flowchart of an exemplary method of manufacturing a polishing instrument according to the present invention.

Figure 8 shows the timewise development of the contact pressure during polishing with a polishing instrument according to a specific embodiment of the present invention.

Figure 9 shows the timewise development of the contact pressure during polishing with a prior art polishing instrument.

Fiure 10 shows a polishing instrument used in obtaining the results shown in fig.

8. In figure 10a, the polishing tool is shown schematically in full view and in close- up view. In figure 10b, the actual tool made is shown.

DETAILED DESCRIPTION OF AN EMBODIMENT

Figure 1 shows a schematic drawing of an exemplary polishing instrument 1 according to the present invention. The length L of the polishing instrument including the shaft 2 and the tip 4, is preferably less than 3mm, and may be less than 2mm, such as is suitable for, polishing, such as micro-polishing. In other embodiments, the length L may be less than 100 mm, such as less than 50 mm, and preferably larger than 20 mm. In many situations, the length may be determined from the interfacing with the machine tool, in the sense that the polishing instrument is fastened in the machine rotating the instrument. The polishing instrument has a cylindrical elongated shaft 2 comprising a tapered neck 3 that progressively decreases in diameter towards the first end 6 of the elongated shaft 2. The tapered neck 3 may have a length greater than 1mm or greater than 2mm, such as between 5 to 10 mm depending on the degree of aspect ratio of the elements to be polished. A longer neck has a more gradual decrease in diameter towards the first end 6 of the elongated shaft, and is thus provides more accessibility to the surface of elements with a higher aspect ratio. The length of the neck 3 is preferably at least one quarter of the length L of the polishing instrument 1, and may have a length as large as half the length L of the polishing instrument 1. A spherical tip 4 having a circular cross section 5 is at the first end of said elongated shaft. The circular cross section 5 is taken from the equator of the spherical tip 4 and has a diameter at least twice as large as the diameter of the first end 6 of the elongated shaft. According to alternative embodiments, the circular cross section 5 may be taken from any location on the tip 4, and may or may not have a diameter larger than the first end of the elongated shaft. The tip 4 has a radius R or equivalent radius of less than 3cm. In other embodiments, the tip 4 has a radius R or equivalent radius of less than 10cm. The tip is configured to perform polishing, the tip 4 having a radius of curvature of less than 500 pm. The radius of curvature of the tip may be less than 450 pm, less than 350 pm or less than 250pm. The tip 4 preferably has its largest dimension less than 1 mm. Such dimensions are advantageous for polishing small-dimension parts or elements, such as optical elements. It is noted that the length of the shaft should preferably be selected while paying attention to the radius of the tip, so that a practicable and useable polishing tool is preferably obtained.

The tip 4 is shown having a preferred spherical shape, because a sphere has constant mean curvature such that the contact area for a given polishing tool offset depends only on the normal vector surface to be polished and on the spherical tip radius. However, according to alternative embodiments of the present invention, the tip 4 is cylindrical or another curved shape, and may have at least one circular cross section. The tip may be an imperfect sphere. The tip 4 has a diameter greater than the diameter of the first end of the elongated shaft. The diameter of the circular cross section 5 of the tip 4 is preferably at least twice as large as the diameter of the first end of the elongated shaft 2. The particular geometry and dimensions of the tool, in particular the spherical tip arranged at the narrow end of a tapered neck and the relative size of the tip cross section diameter to the diameter of the first end of the elongated shaft, is highly advantageous for polishing high aspect ratio profiles. The polishing instrument may be configured to be attached to a robotic finishing machine.

The polishing instrument 1 of this exemplary embodiment is formed of a single thermoplastic and/or thermosetting material that is compatible for both the shaft 2 and the tip 4. The material preferably is hydrophobic and/or porous to hold onto the abrasives while sluffing off fluid during polishing. In other embodiments, the material is hydrophilic and/or porous. The material may comprise polycarbonate (PC), polymethylmethylacrilate (PMMA), polyether ether ketone (PEEK), polystyrene (PS), cellulose acetate (CA), polyethylene terephthalate (PET), polyoxymethlyne (POM), polypropylene (PP), nylon (PA), polyethylene (PE), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), polylactic acid (Pl-A), thermoplastic elastomer (TPE), high density polyethylene (HDPE), epoxy, polyurethane elastomer (PU), Bakelite (phenolic), polyester thermoset (PE), butyl rubber (HR), ethylene-vinyl acetate), acrylonitrile butadiene styrene (ABS), thermoplastic polyurethane (TPU) or any other material having high abrasion resistance and strength. Thermoplastic elastomers (TPE) are a preferred material for at least the tip, since elastomers have high abrasion resistance and can reconfigure themselves if stress is applied. The preferred type of thermoplastic elastomer is TPU, which has the best abrasion and tear resistance of the TPEs and very high strength. According to alternative embodiments of the present invention, the tip is formed of at least one thermoplastic and/or thermosetting material with the shaft formed of one or more different materials, and the tip and the shaft may be connected via mechanical and/or chemical interlocking, as will be further described hereinbelow.

In embodiments, where the tip 4 is porous, the average pore size may be in the order of 3-5 microns.

The polishing tool 1 of this exemplary embodiment is formed as a single unified body of a thermoplastic and/or thermosetting material, allowing the tool 1 to be manufactured in a fast and cost effective manner. It is possible form the tool by using bulk material and machining the polishing instrument with subtractive manufacturing to the final desired shape, or to manufacture the polishing tool with processes such as injection molding, micro-injection molding, casting, or additive manufacturing. It is preferred that the material of the tip 4 to be substantially perfectly elastic and thus spring back completely and immediately. The polishing instrument 1 preferably has a compression set greater than 10% and less than 50% such that it avoids shape memory effect to an optimal degree and is configured to be used with rotational and/or vibrational motion in contact with an element. This preferred range of compression set values allows the material of the polishing tool to not go back completely to its original shape after being pressed or while doing polishing. The increased footprint (i.e. contact area of the polishing tool on an element to be polished, such as a workpiece) of the polishing tool having an optimal compression set between 10% and 50% improves the polishing performance, for example the material removal rate of the polishing tool.

Enlarging the footprint of the polishing tool against the element to be polished enables a larger area to be polished by a tool of a given size, and is therefore particularly useful for polishing, such as micro-polishing and for polishing high aspect ratio elements. The compression set may be less than 40% or less than 30%. The polishing instrument 1 preferably has abrasion resistance less than 20mm3 (e.g. determined based on ISO standard 4649 and may withstand forces up to 50 Newtons. The dimensions and geometry of the polishing tool 1 allow the polishing tool 1 to have a runout lower than 15 pm, and preferably lower than 10pm during polishing use. Forming the tool as a single unified body, such as via injection molding or micro-injection molding, further contributes to decreased runout.

When the tip 4 and shaft 2 are formed of the same material, this allows the possibility for the tip 4 and shaft 2 to be formed together, which is an advantage for maintaining sufficient strength of the connection between the tip 4 and the shaft 2 when the tip to has a diameter substantially greater than the diameter of the first end of the elongated shaft, for example twice or three times the diameter. This geometry, in combination with a long tapered neck 3 as compared to the length L of the entire polishing instrument, the length of the neck 3 preferably being at least one quarter of the length L of the polishing instrument, allow the polishing tool 1 to reach difficult areas of high aspect ratio surfaces while still withstanding the required forces and providing sufficient abrasion.

Reference is made to Figure 2, showing a schematic drawing of an alternative exemplary polishing instrument 1 according to the present invention, having an inner core 7 centrally located to the shaft 2. This alternative embodiment shares many features with the polishing instrument described in accordance with Figure 1; only the features different from those in Figure 1 will be discussed. Instead of a spherical tip, the polishing instrument 1 has a cylindrically shaped tip 4 having a circular cross section 5 and a radius R or equivalent radius less than 3cm. Since the tip is cylindrical, multiple circular cross sections of the tip have a diameter at least twice as large as the diameter of the first end 6 of the elongated shaft 2.

The inner core 7 generally serves as reinforcement to the tool 1, and may have a strength greater than the strength of the material surrounding said inner core.

The inner core 7 is formed of a different material from the material forming the remaining part of the shaft and tip of the polishing tool 1. The inner core extends from a second end 8 of the elongated shaft 2 and along the majority of the length of the elongated shaft through at least a part of the neck 3. The inner core 7 allows the tip 4 to be optimized for a specific application without any compromise of the shaft material, while still allowing efficient manufacturing processes. For example, if the desired material for the tip 4 is TPU but a stronger material is desired for the shaft, then the tool may still be formed almost entirely of TPU via the efficient process of injection molding or micro-injection molding, with the small adjustment of adding a reinforcement. Since the tip may still be formed together with the shaft as a unified body, this allows the tool to retain the advantageous structure for polishing high aspect ratio profiles as discussed hereinabove in accordance with Figure 1. If the tool is manufactured with casting, injection molding, micro-injection molding, or additive manufacturing, then the reinforcing inner core can be placed in the mold, and the tip material may be cast around the inner core or added subsequently. Multi-material injection molding, such as multi-component injection molding, multi-shot injection molding, two- component injection molding, or over molding may be used to form the inner core inside the shaft. Two-component injection molding allows both the core material and outer shaft material to be injected simultaneously, thus further increasing efficiency of manufacturing. The tool 1 is thus formed of two materials: one material forming the centrally located inner core, and a second material forming the remaining part of the shaft and the tip, or according to alternative

embodiments of the present invention, a second material forming the remaining part of the shaft with the tip being formed of the same material as the core or of a third material.

According to a further embodiment of the present invention, the polishing instrument 1 is formed of at least two different materials, with a first material for the tip 4 and a second material for the shaft 2. The materials used may be those described in accordance with the first embodiment, such as thermoplastic elastomers. Forming a tip and shaft of different materials may be advantageous when a removable, interchangeable tip is desired or when the particular material requirements of the tip do not match those of the shaft. The tip and shaft may be also be formed of different materials when a tip is overmolded onto a pre-existing shaft of the polishing tool. Overmolding a tip onto a pre-exsiting shaft requires high-precision alignment of the mold with the shaft such that runout of the polishing tool is reduced. This may further be advantageous when it is desired to reuse an existing shaft for a different purpose by overmolding a tip onto the existing shaft. Any of the following embodiments having a tip and shaft of different materials may further comprise an inner core as described in accordance with Figure 2.

When the instrument 1 is formed of at least two different materials, with a first material for the tip 4 and a second material for the shaft 2, the tip 4 and the shaft 2 according to the present invention are preferably connected at least via mechanical interlocking. The mechanical interlocking may be supplemented by chemical interlocking, or in particular cases the tip and shaft may be connected purely by chemical interlocking. Two-component injection molding (2K IM) is a preferred method of manufacturing the tool when different materials are required for the shaft and tip, since 2K IM does not require alignment of the shaft with the tip, decreasing the runout.

Figures 3A -3B show schematic drawings of alternative exemplary polishing instruments 1 according to the present invention, having a preferred structure for mechanical interlocking, wherein the shaft 2 has a locking element 9 for mechanical interlocking with the tip 4. This allows the shaft and tip to be formed separately of different materials and subsequently connected or molded together, such as overmolding the tip 4 onto a previously molded shaft 2. The mechanical interlocking is achieved by the first end of the elongated shaft comprising a locking element 9 protruding from the first end of the elongated shaft configured to fit inside the tip 4. Fig. 3A shows a locking element 9 that is T-shaped arranged at the first end 6 of the elongated shaft 2, and Figure 3B shows a locking element 9 that is rod shaped. These shapes are particularly advantageous because they secure the tip along two perpendicular directions, thus preventing the spherical tip from sliding in the tangential direction when polishing is performed. Although the rod shaped and T-shaped locking elements are preferable, other shapes of undercuts may be used to secure the tip to the shaft.

Although the tip 4 is spherical in these drawings, the tip may alternatively be cylindrical or another curved shape, or a prismatic shape, and may have at least one circular cross section. Although no inner core is shown in this drawing, the tool according to this embodiment may further comprise an inner core. The inner core may be made of the same material as the tip, or of a different material such that the tool may be comprised of up to three different materials.

Reference is made to Figures 4A to 4C, showing schematic drawings of an alternative exemplary necks 3 of the polishing instrument according to the present invention that are configured to allow mechanical interlocking of the tip. The shafts are depicted without the tip 4 to highlight the structural features, such as they would appear prior to molding or attaching the tip 4.

Fig. 4A shows an exemplary polishing tool 1 having threads 10 along at least part of the neck 3. The threads create undercuts where the material can flow into if the tip 4 is molded onto the neck 3. Alternatively, the tip 4 may have complementary threading that enables the tip to be removed and reattached to the shaft. If multiple tips 4 are compatible with the shaft, the tips may be interchangeable while retaining the same shaft. Since the requirements for polishing different elements are unique and varied, this provides an advantageous flexibility of the polishing tool.

Fig. 4B shows an exemplary polishing tool 1 having a cross hole 11 in the neck 3 of the elongated shaft. According to alternative embodiments of the present invention, there may be multiple cross holes 11. The one or more cross holes may be manufactured on the shaft during injection molding. The tip may be injection molded, and when the tip is injected, the polymer tip material flows into the hole to embrace the shaft. A strong chemical and mechanical bonding may be created. Fig. 4C shows an exemplary polishing tool 1 having surface texturing 12 of the elongated shaft that is configured to allow the tip 4 to adhere to the elongated shaft. The surface texturing 12 enhances mechanical adhesion between the shaft and the tip.

According to any of these embodiments, the mechanical interlocking may be supplemented by chemical interlocking due to material compatibility.

The mechanical interlocking structures of the present invention are an advantage for maintaining sufficient strength of the connection between the tip and the shaft when the tip has a cross sectional diameter substantially greater than the diameter of the first end of the elongated shaft, for example twice or three times the diameter. This allows the polishing tool 1 to have a different material for the tip and shaft while maintaining this desired geometry that allows the polishing tool to reach difficult areas of high aspect ratio surfaces, while still withstanding the required forces and providing sufficient abrasion.

Reference is now made to Figure 5, showing a further exemplary embodiment of the present invention wherein an outer tip 13 is arranged over an existing polishing tool. The outer tip 13 may be overmolded onto the existing tip 4 and neck 3. This allows flexibility in the manufacturing process while still providing a tool suitable for polishing high aspect ratio profiles. The outer tip 13 may be formed of a different material than that of the original tip 4. In addition to allowing a pre-existing shaft and/or tip to be reused, the tool according to this embodiment has the advantage that runout of the polishing tool is reduced, due to the manufacturing process that involves high-precision alignment of a mold for forming the tip with the pre-existing shaft. Figure 6 shows a schematic drawing of the exemplary polishing instrument according to any of the previous

embodiments, wherein the tip 4 has an outer coating 14, preferably coating of a uniform thickness. The coating may be fixed or removable from the tip 4. The coating may be attached to the tip due to mechanical and/or chemical

interlocking, such as by surface texturing. The coating may be achieved with spin coating. The coating may be a single layer or comprise layers of different materials. This embodiment is particularly advantageous because it allows re coating or replacement of the tip 4 when a tool is starting to wear. Figure 7 shows a flowchart of an exemplary method of manufacturing a polishing instrument using injection molding according to the present invention. In step 15, a mold is provided. The mold may be shaped to form an entire polishing instrument having a tip and a shaft, or preferably to form a tip of a polishing instrument onto or over an existing shaft and/or existing tip. The mold may be formed to accommodate a previously formed portion of the polishing tool. The portion of the mold for forming the tip is shaped in a curved shape, such as a spherical or cylindrical shape, to form a tip having a radius or equivalent radius of less than 3cm, and preferably having a radius of curvature of less than 500 pm and at least one circular cross section. According to alternative embodiments of the present invention, the portion of the mold for forming the tip is shaped in a prismatic shape. The mold is preferably shaped to form a tip having its largest dimension less than 1 mm, as is especially advantageous for micro-polishing of high aspect ratio profiles. However, the dimension of the tip may in other embodiments differ from being less than 1 mm or larger than 1 mm as otherwise disclosed herein. The dimensions and shape of the mold should be optimised depending on the materials to allow for shrinkage.

If the mold is shaped to form an entire polishing instrument, the mold comprises a portion shaped to form an elongated shaft. This portion of the mold should be shaped to form a tapered section towards the first end of the elongated shaft, to become the neck of the shaft. When the mold is configured to form at least a part of an elongated shaft, the mold is preferably shaped and has dimensions to form a shaft having its smallest dimension less than 500pm. When the mold is configured to form an entire polishing instrument, the mold is preferably shaped and has dimensions to form a polishing instrument having length L less than 3mm. In other embodiments, the length L is larger than 40 mm, such as larger than 100 mm, and smaller than 10 mm. The mold may be shaped for forming a polishing instrument having a length L less than than 2mm.

In step 16, thermoplastic and/or thermosetting materials, preferably including at least one thermoplastic elastomer, are compounded to form a polymer compound material. These materials provide a polishing instrument having a compression set such that the polishing instrument is configured to be used with vibrational and/or rotational motion in contact with an element for successful polishing. The compression set of the polishing instrument is preferably larger than 10% e.g. when one would like to increase the footprint during polishing and less than 50%, and may be less than 40% or less than 30% otherwise. During this step, micro abrasive grains, such as alumina or diamond grains, may be incorporated into the material to be injected into the mold. This is performed by heating and mixing a desired proportion in weight of micro-abrasive grains relative to the weight of the polymer compound material into the polymer compound material, and

compounding the polymer compound material comprising the micro-abrasive grains, such as with a twin extruder, to achieve a desired dispersion and homogeneity. The desired proportion in weight of micro-abrasive grains relative to the weight of the polymer compound material is preferably between 0.3% and 0.5%. This novel method of uniformly dispersing the grains contributes to the production of a polishing tool that is ready for use in polishing immediately after removal from the mold. This step may further involve compounding the polymer compound material with soluble particles and subsequently dissolving them to achieve a desired porosity of the polishing instrument.

In step 17, the compound material, which may comprise micro-abrasive grains and/or soluble particles, is injected into the mold to preferably form the tip, or alternatively to form the entire polishing instrument. When a tip is being overmolded onto a pre-exsiting shaft, the method comprises performing high- precision alignment of the mold with the pre-existing shaft, which enables runout of the polishing tool during polishing to be reduced. In step 18, at least the tip of the polishing instrument is removed from the mold. In step 19, the polishing instrument is ready to be used for polishing immediately after removal from the mold. The method may further comprise forming a coating on the tip, such as by spin coating, to achieve an optimal thickness distribution of the tip.

According to alternative embodiments of the method of manufacturing the polishing instrument of the present invention, the shaft 2 may be formed via extrusion, MIM, turning, ECM, casting, injection molding, or 3D printing, and the tip may be formed via micro casting, spray coating, injection molding or 3D printing. The presently disclosed methods of manufacturing and structure of the presently disclosed polishing instrument, in particular the unique geometry and dimensions of the polishing instrument and the use of injection molding to form the tool, advantageously result in a polishing tool that may be used with minimal runout. The disclosed method of overmolding a tip onto an existing shaft and/or tip is particularly advantageous in providing a polishing tool that may be used with minimal runout. A method of polishing, such as micro-polishing an object by use of the polishing instrument is provided according to the present invention, the method comprising applying a force to the polishing instrument 1, such as between 1 and 50 Newtons. The method preferably further comprises applying a rotational speed to the polishing instrument 1 of at least 100, such as at least 2.000 rpm while maintaining a runout of the polishing instrument 1 less than lOpm. Furthermore, the presently disclosed materials and compression set of the disclosed polishing instrument are advantageous for providing an increased footprint of the polishing tool while polishing, which is associated with an improved material removal rate. The method may comprise applying rotational and/or vibrational motion to the polishing instrument while achieving a larger footprint than a polishing tool having a tip of the same dimensions and having a compression set lower than 10% or larger than 50%.

EXPERIMENTS AND MENTIONING OF SOME MATERIALS

With reference to figs. 8 and 9 further details and considerations are presented. These details should not be taken as limiting for the scope of the invention. Based on some requirements for implementation of deterministic polishing outlined herein, rotating long neck tools with small diameter shafts and spherical tips are found to be well suited for micro polishing. The long neck and small diameter guarantee access to small surface cavities with high aspect ratio. The spherical shape of the active part of the tool favours the consistency of the contact area when complex geometries are polished. The tool tip material is in some embodiments chosen to be a thermoplastic polyurethane in order to minimize permanent deformations and consequent geometrical variations when subjected to prolonged loading as occurs during polishing. To ensure consistency of tool geometry and material properties between different tools, the selected tool manufacturing process may comprise of overmoulding of polyurethane on commercial shafts, thereby greatly reducing tool production time and avoiding individual tool preparation.

As the tool tip is made of polymer, it is subject to contact pressure stabilising.

This is a time dependent phenomenon, due to the viscoelastic behaviour of polymers, and consists in a decrease in stress in response to a nominal constant strain. In polishing, this implies that, after applying the initial offset, the contact pressure decreases with time and so does the material removal rate. Depending on the characteristics of the specific polymer used, contact pressure decrease due to contact pressure stabilising can induce considerable form errors during polishing. The time necessary to reach contact pressure stabilization may be an important parameter in characterizing relaxation. If the stabilization time is small, the contact pressure reduction takes place immediately after the application of offset, and therefore does not influence the MRR during polishing.

In fig. 8 (see also fig. 10) a tool made from a compound of two different thermoplastic polyurethane, with a compound fraction of 50/50 wt% is used. For some tools developed, see fig. 8, and in specific operating conditions (i.e. initial offset corresponding to specific initial load) while the initial load is reduced by nearly 25%, from 1.2 N to approximately 0.9 N, the effect of relaxation occurs within approximately 60 s from load application, after which a stable load value is reached. As a result, for the developed polishing tools, the effect of relaxation on the material removal rate can be neglected during a polishing operation since it is limited to the short initial phase. For comparison, commercial polishing tools made of polyurethane LP66 were tested with the same procedure, showing a load decrease of 43% reaching stabilization in approximately 8 minutes (Fig. 8).

Micro-polishing tool for obtaining results of fig. 8: Based on the requirements for implementation of deterministic polishing outlined above, rotating long neck tools with small diameter shafts and spherical tips are found to be well suited for micro polishing (Fig. 10a). The long neck and small diameter may provide access to small surface cavities with high aspect ratio. The spherical shape of the active part of the tool favours the consistency of the contact area when complex geometries are polished. Thus, as an example, tools with radius of 400 pm and neck length of 2.3 mm have been developed (Fig. 10b). The tool tip material was chosen to be a thermoplastic polyurethane in order to minimize permanent deformations and consequent geometrical variations when subjected to prolonged loading as occurs during polishing. Finally, to ensure consistency of tool geometry and material properties between different tools, the selected tool manufacturing process consists in overmoulding of polyurethane on commercial shafts, thereby greatly reducing tool production time and avoiding individual tool preparation. The runout error of the produced tools was characterized with a laser triangulation

displacement sensor Micro Epsilon Opto NCDT 2300 to scan the tool surface with the tool rotating on a precision spindle. The resulting average runout was

±4.1pm.

Experimental set-up: To provide accurate control of relative tool-workpiece motion and orientation, as well as sufficient tool rotational accuracy, polishing

experiments are performed on a 4 axis CNC machine Robodrill from Fanuc adapted for polishing purposes. The workpiece material used consists of diamond- turned flat nickel- phosphor disks. The used abrasives are 0.2 pm size alumina particles dispersed in a slurry with low viscosity to improve the slurry's flow and promote a uniform distribution of abrasives in the polishing area. The slurry is then continuously pumped towards the polishing area assuring constant and uniform distribution of abrasives. CAM programs were generated using the ZephyrCAM software developed by Zeeko Ltd.

The material removal rate is characterized by a spot polishing experiment, whereby the tool is plunged onto the surface for a few seconds. Corrective polishing is realized by performing a numerical deconvolution between the surface topography and removal footprint, which yields a dwell time map. By considering the distance between tool path points, these dwell times are finally converted to tool feed variations. The topography of all test surfaces was measured before and after polishing on a Wyko RTI4100 Fizeau laser interferometer with < 1 nm measurement repeatability. The best fit-plane was removed and cubic

interpolation was used to resample both datasets to a common grid so that they could be subtracted. No filtering was applied. Abrasives

Abrasives suitable for polishing in relation with the present invention may preferably consist of hard particles of e.g. silicon carbide, aluminum oxide, boron carbide, cerium oxide, zirconium oxide, cubic boron nitride, diamond, as well as their combinations. The abrasive particles, typically with mean below 20 pm (most typically between 15 pm and 0.01 pm), are preferably dispersed in a carrier fluid, which can be water based, ethanol based, oil based, glycerol based or have other bases. Abrasives concentration can be in the range of 0.0001% to 5% in weight. Polymer materials and mixing fractions

For the production of the tip, compounds of two or more polymer materials can be used. Compounding can for instance be carried out with a twin extruder. As examples, possible polymer material combinations and mixing ratios for combinations of materials will be disclosed in the following. It is noted that the examples provided are non-limiting examples.

Materials

It is noted that if the tip is not made of a compound, the tip can be made from one of the materials listed. Mixing ratios

In the following table, different preferred and non-limiting mixing ratios for the materials listed in the above table are presented :

It is noted that an empty cell in the above table does not indicate that the two materials are non-compatible and cannot be mixed. The filled-out cells represent the presently preferred combinations.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. Dimensions presented herein are meant as being illustrative and should be used to limit the scope of the invention. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a

combination of features is not possible and advantageous. ITEMIZED LIST OF EMBODIMENTS

In the following preferred embodiments of the invention are presented as an itemized list of embodiments.

Item 1. A polishing instrument (1) comprising :

an elongated shaft (2) comprising a neck (3), said neck being tapered towards a first end (6) of said elongated shaft; and

a tip (4) having a shape, such as a curved shape, configured to perform polishing at the first end of said elongated shaft, said tip being formed of at least one thermoplastic and/or thermosetting material and having a radius (R) or equivalent radius of less than 3cm.

Item 2. A polishing instrument (1) according to item 1, wherein said polishing instrument (1) has a compression set larger than 10% and smaller than 50% such that it is configured to be used with rotational and/or vibrational motion in contact with an element.

Item 3. A polishing instrument (1) according to either of items 1 or 2, wherein said tip (4) has a radius of curvature of less than 500pm.

Item 4. A polishing instrument (1) according to any of the previous items, wherein said polishing instrument (1) has a compression set less than 40%.

Item 5. A polishing instrument (1) according to any of the previous items, wherein said tip (4) has one or more circular cross sections (5). Item 6. A polishing instrument according to item 5, wherein at least one of said one or more circular cross sections (5) of said tip (4) has a diameter at least twice as large as the diameter of the first end (6) of the elongated shaft (2).

Item 7. A polishing instrument according to any of the previous items, wherein said tip (4) has its largest dimension less than 1 mm.

Item 8. A polishing instrument according to any of the previous items, wherein said elongated shaft (2) has its smallest dimension less than 500pm. Item 9. A polishing instrument according to any of the previous items, wherein said polishing instrument (1) has a length (L) less than 3mm.

Item 10. A polishing instrument according to any of the previous items, wherein said at least one thermoplastic and/or thermosetting material comprises a thermoplastic elastomer.

Item 11. A polishing instrument according to any of the previous items, wherein said elongated shaft (2) further comprises an inner core (7), said inner core (7) extending from a second end (8) of said elongated shaft (2) and along the majority of the length of said elongated shaft (2) through at least a part of said neck (3).

Item 12. A polishing instrument according to any of the previous items, wherein said tip (4) and said elongated shaft (2) are removably connected.

Item 13. A polishing instrument according to any of the previous items, wherein said tip (4) and said elongated shaft (2) are connected at least via a mechanical interlocking that is achieved by at least one of:

a. at least one undercut in the elongated shaft (2);

b. a rod shaped or T-shaped locking element (9) extending from the first end of said elongated shaft configured to fit inside said tip; c. at least one cross hole (11) in the shaft;

d. surface texturing (12) of the elongated shaft (2) configured to allow the tip to adhere to the elongated shaft;

e. interlocking threads (10) on the elongated shaft (2); and f. said tip (4) having a shape configured to increase the contact area and consequently the adhesion force between said tip (4) and said elongated shaft (2).

Item 14. A polishing instrument according to any of the previous items, wherein said tip (4) and said elongated shaft (2) are connected at least via chemical interlocking due to material compatibility. Item 15. A polishing instrument according to any of the previous items, wherein said polishing instrument (1) is formed entirely of a single thermoplastic and/or thermosetting material. Item 16. A method of micro-polishing an object by use of the polishing instrument (1) according to any of the previous items, further comprising applying a force to the polishing instrument (1) while applying a rotational speed to the polishing instrument (1) of at least 2.000 rpm and while maintaining a runout of the polishing instrument (1) less than lOpm.

Item 17. A method for forming a polishing instrument using injection moulding, comprising:

i) providing a mold shaped to form at least the tip (4) of a polishing instrument (1) comprising an elongated shaft (2) and a tip (4) at a first end of said elongated shaft (2), said tip (4) having a radius (R) or equivalent radius of less than 3cm and shape, such as a curved shape configured to perform polishing, said elongated shaft (2) comprising a neck (3), said neck (3) being tapered towards said first end of said elongated shaft;

ii) compounding thermoplastic and/or thermosetting materials to form a polymer compound material;

iii) subsequently injecting said compound material into said mold to form at least said tip (4), thereby providing said polishing instrument (1) as a unified body comprising said tip (4) and said elongated shaft (2); and

iv) removing at least said tip (4) of said polishing instrument (1) from said mold such that said polishing instrument (1) is removed from said mold. 18. A method according to item 17, wherein said polishing instrument (1) has a compression set larger than 10% and less than 50%, such that said polishing instrument is configured to be used with rotational and/or vibrational motion in contact with an element immediately after removal from the mold. Item 19. A method for forming a polishing instrument (1) using injection moulding according to either of items 17 or 18, the method further comprising the steps of: a) heating and mixing a desired proportion in weight of micro-abrasive grains relative to the weight of said polymer compound material into said polymer compound material, and

b) compounding said polymer compound material comprising said micro-abrasive grains to achieve a desired dispersion and homogeneity,

said steps a) and b) being performed prior to said injection of said compound material into said mold.

Item 20. A method for forming a polishing instrument (1) using injection moulding according to item 19, wherein step b) comprises compounding said polymer compound material comprising said micro-abrasive grains with a twin extruder.

Item 21. A method for forming a polishing instrument (1) using injection moulding according to any of items 17-20, wherein step i) comprises providing a mold shaped to form at least the tip (4) of a polishing instrument (1), wherein said tip (4) has a radius of curvature of less than 500pm.

Item 22. A method for forming a polishing instrument (1) using injection moulding according to any of items 17-21, wherein step i) comprises providing a mold shaped to form at least the tip (4) of a polishing instrument (1), wherein said tip (4) has at least one circular cross section (5).

Item 23. A method for forming a polishing instrument (1) using injection moulding according to any of items 17-22, wherein step iii) comprises subsequently injecting said compound material into said mold to form only said tip (4) onto a pre-existing shaft and/or pre-existing tip of said polishing instrument (1).