Field of the Invention

The present invention relates to a polishing tool arrangement for uniform polishing the knee implant. More particularly, the present invention relates to the polishing tool arrangement for uniform polishing the knee implant wherein a strong permanent magnet is appropriately attached to a mu-metal cylindrical fixture with the help of Allen bolts. This invention relates to the polishing tool arrangement for uniform polishing the knee implant wherein the magnet (11) and their fixture (3) are maintaining an optimum gap of 0.6 mm from the curved surfaces of the knee implant. The present invention relates to the polishing tool arrangement for uniform polishing the knee implant wherein fine polishing is achieved, surface roughness of the polished part is improved to a high level, and the requirement of human body implantation is met.

Background of the invention and related prior Art

Three types of variable-torque brakes have been employed in prosthetic knees in the past: (i) dry friction brakes where one material surface rubs against another surface with variable force; (ii) viscous torque brakes using hydraulic fluid squeezed through a variable sized orifice or flow restriction plate; and (iii) magnetorheological (MR) brakes or dampers where MR fluid (containing small iron particles suspended in the fluid) is squeezed through a fixed orifice or flow restriction plate, with viscosity of the fluid being varied in response to an applied magnetic field. Each of these technologies, as conventionally practiced in the field of prosthetics, can pose certain disadvantages.
The magnetorheological (MR) fluid is a smart fluid that changes its property according to the nature of the applied magnetic field and has found many applications in modem manufacturing sectors. Some of these applications include optics manufacturing, dampers, brakes, clutches, hydraulic valves, seals, composite structures, and polishing devices. The nanoscale finishing oflarge-scale parts with complex geometric features using the magnetorheological fluid-based finishing process is perhaps the most effective MR fluid application.
There are five significant aspects to this technology, the placement of magnet to generate the required value of the concentric magnetic field at the end of the polishing tool, magnet fixture made up of mu-metal, an arrangement made to properly hold the knee implant and attached to 4th axis chuck (2a) for simultaneous rotation, optimum tool path generation and selection of proper rotational speed of the polishing tool to generate high-quality knee implants surfaces without defect or tool marks, synthesis of new MR. fluid to form required amount of oxide layer on implant surfaces to enhance the bio-compatibility property of implants material.
The concentration of the necessary magnetic field at the polishing tool is initially checked for uniform magnetic field generation to finish the knee implant's freeform surfaces properly. A concentrated MR. fluid with 0.6 mm thickness between the polishing tool and implant profiles is consistently maintained throughout the finishing procedure using the CNC controller to get uniform polishing. This much thick MR. fluid ensures maximum catchment of abrasive particles across the iron particle chains to get effective contact to the implant's curved profiles and, thus, better process economics. The magnet characteristics such as placement, orientation, magnet size, and strength affect process efficiency and surface finishing performance. The magnets should be optimally fixed inside the fixture; otherwise, the required uniform magnet field concentration will not be present at the end of the polishing tool. For this purpose, the Mu-metal (nickel-iron alloy)
magnet fixture is used to direct the magnetic flux lines. In the finishing zone, the magnetic flux density is concentrated on the workpiece surface, which results in a higher uniform finishing rate. Also, the fixture shields the magnetic field from the outside environment so that MR. fluid and any surrounding magnetic materials do not stick to the magnet fixture. Also, the magnet should have a specific orientation; it means the magnet's north or south-pole facing orientation should be decided based on the uniformity of the magnetic field distribution. The magnet's size will also affect magnetic field distribution; its size variation determines the magnet fixture size.
The necessary implant surfaces can be generated depending upon the requirements with the help of a specific composition of MR. fluid. A spiral or parallel tool path is generated using sprutcam® software to finish the surfaces of the implant properly. However, it is found that a parallel toolpath gives the best surface finish, surface topography, and surface texture to knee implants profiles without defects or tool marks.
The document Shengyue Zeng et al (2019) illustrates artificial prostheses are widely used to replace the damaged, worn, or diseased bone and cartilage around joints, improving patient’s quality of life. To ensure optimum functionality and the lifespan of a joint replacement system, the bearing surfaces of prostheses are required to be polished to nanometer-scale surface texture and micrometer-scale form tolerance. In this chapter, polishing technologies used for artificial implant surface finishing are introduced. It starts with an overview of hip replacement and knee replacement and followed by the literature review on the biomaterials for arthroplasty components and the general processes for the manufacturing of arthroplasty components. The ultra-precision polishing technologies for finishing the load-bearing surfaces of artificial joints are introduced in terms of polishing technologies, material removal mechanism, surface roughness improvement, and form correction. Different types of polishing technologies which can be potentially used for artificial joints in the future are also reviewed, and special attention is paid to the bonnet polishing technology.
According to the document US7101487 the invention is directed to magnetorheological fluids utilized in prosthetic joints in general and, in particular, to magnetorheological fluids utilized in controllable braking systems for prosthetic knee joints. Preferred magnetorheological fluids of the present invention comprises polarizable iron particles, a carrier fluid, and optionally an additive. Preferred additives include, but are not limited to functionalized carrier fluids as well as derivative fluoropolymers. Preferred carrier fluids include, but are not limited, to perfluorinated polyethers.
The invention of the document US5804095 is directed to the A magnetorheological fluid comprises non-colloidal magnetic particles, an abrasive, water, glycerol, and an alkaline buffer. The abrasive may be CeO2, the non-colloidal magnetic particles may be carbonyl iron, and the alkaline buffer may be Na2 CO3. The fluid is useful for magnetorheological finishing.
The other document Iskander El-Amri et al (2018) said that a novel magnetic concentration setup for localized finishing of freeform surfaces based on employing electro permanent magnet arrays configured using a recently developed magnetic concentration principle. The setup, without the use of any rotating or moving component, is capable of creating a localized spatiotemporal magnetic field variation a specialized magnetic fluid to polish a target 1.5cm2 area on the workpiece surface. Using a computational mechanistic model as well as experimental studies, we show that the current configuration of electro permanent magnets is capable of amplifying the magnetic strength by almost 3 times near the workpiece surface in comparison to no magnetic concentration. We also show that by modulating the strength, including toggling the polarity of electro permanent magnets, we demonstrate the sloshing motion of the fluid at a targeted region without requiring any rotating part. Experimental investigations on the localized removal of acrylic paint from a cylindrical workpiece surface suggest that the method can be used to polish localized, hard-to-access freeform geometries.
The document Sunpreet Singh et al (2020) illustrates the potential of magneto-rheological fluid assisted abrasive finishing (MRF-AF) for obtaining precise surface topography of an in-house developed ß-phase Ti-Nb-Ta-Zr (TNTZ) alloy for orthopedic applications. Investigations have been made to study the influence of the concentration of carbonyl iron particles (CIP), rotational speed (Nt), and working gap (Gp) in response to material removal (MR) and surface roughness (Ra) of the finished sample using a design of experimental technique. Further, the corrosion performance of the finished samples has
also been analyzed through simulated body fluid (SBF) testing. It has been found that the selected input process parameters significantly influenced the observed MR and Ra values at 95% confidence level. Apart from this, it has been found that Gp and Nt exhibited the maximum contribution in the optimized values of the MR and Ra, respectively. Further, the corrosion analysis of the finished samples specified that the resistance against corrosion is a direct function of the surface finish. The morphological analysis of the corroded morphologies indicated that the rough sites of the implant surface have provided the nuclei for corrosion mechanics that ultimately resulted in the shredding of the appetite layer. Overall results highlighted that the MRF-AF is a potential technique for obtaining nano-scale finishing of the high-strength ß-phase Ti-Nb-Ta-Zr alloy.
Summary of the invention

The present invention relates to a polishing tool arrangement for uniform polishing the knee implant. More particularly, the present invention relates to the polishing tool arrangement for uniform polishing the knee implant wherein a strong permanent magnet is appropriately attached to a mu-metal cylindrical fixture with the help of Allen bolts. This invention relates to the polishing tool arrangement for uniform polishing the knee implant wherein the magnet (11) and their fixture (3) are maintaining an optimum gap of 0.6 mm from the curved surfaces of the knee implant. The present invention relates to the polishing tool arrangement for uniform polishing the knee implant wherein fine polishing is achieved, surface roughness of the polished part is improved to a high level, and the requirement of human body implantation is met.

Detailed description of the invention

The previous studies related to the freeform surface finishing show that it is challenging
to achieve uniform polishing due to its shape. The shape of the freeform surface does not
conform to conventional surface shapes like planes, cones, cylinders, etc. Medical, aerospace and automobile industries require nanometer-level finishing of freeform surfaces. Surface roughness is a crucial element to predict the performance of a component in the real environment. Components with rough surfaces suffer more from corrosion and component failure. Surface roughness affects the operational efficiency of the component. Previously, utilized conventional finishing is a time-consuming, labor-intensive, error-prone, and costly process. These processes cause tensile stresses and shocks, resulting in circumferential scratches. Tool marks, scratches, burrs, dents, or pits deteriorate the surface quality of these freeform profiles. Also, the previously studied methods do not enhance the bio-compatibility property of implants material, yet they decrease the capacity of this property. Proper uniform surface finishing of knee implant is also not achieved, especially for Ti-alloy implant, which can cause a very high risk of blood clogging inside the human body, thus resulting in serious problems.

The principal object of the present invention is to provide a polishing tool arrangement for uniform polishing the knee implant.
Another object of the present invention is to provide a polishing tool arrangement for uniform polishing the knee implant which consists of a) custom-made 4th axis setup (2a) wherein Space (5, 5a) is provided in the magnet fixture for placing the magnet, b) cylindrical permanent magnet, c) The small flat surface ( 6) on this magnet fixture so that proper space can be provided for holding the magnetorheological fluid at the end of the polishing tool; d) a threaded hole ( 4, 4a) is made to properly tighten the magnet inside the fixture by using the Allen bolt (8); e) The extruded rod part (7) on the magnet fixture; f) the support hub (19) for perfectly aligning the knee holder horizontally to the 4th axis chuck (2a); g) a brass tool holder support (9) of magnet fixture;
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein a strong permanent magnet is appropriately attached to a mu-metal cylindrical fixture with the help of Allen bolts.
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein the magnet (11) and their fixture (3) are maintaining an optimum gap of 0.6 mm from the curved surfaces of the knee implant.
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein fine polishing is achieved, surface roughness of the polished part is improved to a high level, and the requirement of human body implantation is met.
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant which is rotated at an optimum rotational speed through a CNC milling machine head.
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein CNC controller controls the custom-made 4th axis spindle chuck (2a).
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein custom-made 4th axis spindle chuck (2a), externally connected to a 3-axis CNC milling machine bed.
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein the magnetorheological (MR) fluid which consists of 40 volume % Carbonyl iron particles ( CIPs ), 7.1 volume % diamond abrasive particles, 8 volume % glycerol, 1.3 volume % hydrogen peroxide (H2O2) and 43.6 % deionized water.
Another object of the present invention is to provide the polishing tool arrangement for uniform polishing the knee implant wherein the brass tool support (9), which is tightly attached to magnet fixture (3).

The novel features that are considered characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of certain specific embodiments, when read in connection with the accompanying drawings, in which:

FIG. 1 illustrates the 4th axis setup (2) for knee implant and comprehensive milling machine head holding the polishing tool (I). of the present invention;
FIG. 2 illustrates the polishing tool tightly holding the magnet along with their support of the present invention;
FIG. 3 illustrates the space provided inside the polishing tool for adequately placing the magnet and tightened by using Allen bolts in provided threaded holes ( 4a) of the present invention;
FIG. 4 illustrates the tool support (9) for the mu-metal magnet fixture to prevent it from unwanted experimental circumstances of the present invention;
FIG. 5 illustrates the cylindrical permanent magnet of the present invention;
FIG. 6 illustrates the fixture to properly hold the knee implant in the provided space ( 1 8) and tighten it using an Allen bolt in the provided threaded hole (17) of the present invention;
FIG. 7 illustrates the support for the knee implant holder (15) for neglecting any misalignment with the 4th axis spindle chuck (2a) for properly horizontal placement of the knee holder of the present invention;
FIG. 8 illustrates the knee implant and its finishing freeform curved profiles (24, 25) of the present invention;

A unique polishing tool for uniform finishing the knee implant or complex freeform surfaces is disclosed. A strong permanent magnet is appropriately attached to a mu-metal cylindrical fixture with the help of Allen bolts. This tool design ensures the best possible magnetic field at the freeform finishing surfaces of the knee implant. The magnet (11) and their fixture (3) are maintaining an optimum gap of 0.6 mm from the curved surfaces of the knee implant so that always a direct and uniform lapping of magnetorheological (MR) fluid is maintained to the implant's curved profiles. High-permeable magnetic material (mu-metal) is used as a fixture for proper magnetic field shielding. The developed novel polishing tool is attached to a 4-axis CNC milling machine head (la). Cylindrical brass support (9) is used for the mu-metal fixture to protect the fixture from any uncertain experimental damaging condition and provides thermal stability to the mu-metal fixture. The new composition ofMR fluid is also synthesized to uniformly nano-finish the Ti alloy of grade 5 knee implant curved surfaces. Another fixture (12) is used to hold the knee implant and attached to the fourth axis (2a) to rotate the implant with the polishing tool movement simultaneously.
Fig. 1 schematically illustrates a complete arrangement for uniform polishing of knee implant with its custom-made 4th axis setup (2a). Space (5, 5a) is provided in the magnet fixture for placing the magnet, as illustrated in Fig. 2. The small flat surface ( 6) is also made on this magnet fixture so that proper space can be provided for holding the MR. fluid at the end of the polishing tool. Fig. 3 shows the cross sectional view of the magnet fixture, where a threaded hole ( 4, 4a) is made to properly tighten the magnet inside the fixture by using the Allen bolt (8). The extruded rod part (7) on the magnet fixture is also made to place it into the space provided (10) in the brass tool support made for the magnet fixture.
Fig. 4 shows the brass tool support (9), which is tightly attached to magnet fixture (3) to protect it from unwanted circumstances and provide thermal stability to the magnet fixture when maximum heat is generated inside the tool due to friction. This support has a hub (9a) for tightly fitting the magnet fixture. This brass support also helps in the proper vertical alignment of the magnet fixture to the surface of the knee implant. Fig. 5 shows the cylindrical permanent solid magnet ( 11 ).
Fig. 6 shows the holder for the knee implant. This holder or fixture (12) has various parts with specific requirements. This holder has a base plate (13) from which extruded rods
(14, 15) comes out on both sides, one rod will go inside the 4th axis spindle chuck (2a), and the other will be supported on the vertical support hub (19) made of the brass disk. The hollow cylindrical space (18) is left in the holder to fix the knee implant in the threaded hole properly (17) fabricated on extruded rod (16) by using an Allen bolt (8).
Fig. 7 shows the support hub (19) for perfectly aligning the knee holder horizontally to the 4th axis chuck (2a). This vertical support hub has an extra extruded cylindrical part (20) to match the height of the 4th axis chuck (2a). On the top of this cylindrical part, a semi-circular raceway (22) is made, which diameter is a little bit greater than extruded rod (15) of the knee holder (12). This semi-circular raceway has clearance for placing the rubber or gasket pad (22a) for observing the vibration due to rotation of the knee holder for smooth finishing. This raceway also has flat flange support (21) for properly clamping the extruded rod (15) of the knee holder using another semi-circular raceway (21a) in the provided holes (23, 23a) using Allen bolts. The other raceway also has an arrangement of rubber pads (22b) for observing the vibration of the knee holder during rotation.
Fig. 8 shows the knee joint implant where two freeform finishing surfaces (24, 25) are present. Each freeform surface has two extended profiles (24a, 24b) and (25a, 25b ). This knee joint has support (26), which is used for properly fitting into the bone of the human body. In the current invention, this support (26) is used to fit into the knee holder in the provided space (18).
From the foregoing description, it will be appreciated that novel approaches relating to prosthetic devices, pressure control and handling of slurries and fluids have been disclosed. While the components, techniques and aspects of the invention have been described with a certain degree of particularity, it is manifest that many changes may be made in the specific designs, constructions and methodology herein above described without departing from the spirit and scope of this disclosure.

While a number of preferred embodiments of the invention and variations thereof have been described in detail, other modifications and methods of using and medical applications for the same will be apparent to those of skill in the art. Accordingly, it should be understood that various applications, modifications, and substitutions may be made of equivalents without departing from the spirit of the invention or the scope of the claims.

Various modifications and applications of the invention may occur to those who are skilled in the art, without departing from the true spirit or scope of the invention. It should be understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be defined only by a fair reading of the appended claims, including the full range of equivalency to which each element thereof is entitled.

We Claim:

1) A polishing tool arrangement for uniform polishing the knee implant which consists of
-wherein custom-made 4th axis setup (2a) wherein Space (5, 5a) is provided in the magnet fixture for placing the magnet ;
-wherein a cylindrical permanent magnet ;
-wherein the small flat surface ( 6) on this magnet fixture so that proper space can be provided for holding the magnetorheological fluid at the end of the polishing tool;
-wherein a threaded hole ( 4, 4a) is made to properly tighten the magnet inside the fixture by using the Allen bolt (8);
-wherein the extruded rod part (7) on the magnet fixture;
-wherein the support hub (19) for perfectly aligning the knee holder horizontally to the 4th axis chuck (2a);
-wherein a brass tool holder support (9) of magnet fixture;
2) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein the magnet (11) and their fixture (3) are maintaining an optimum gap of 0.6 mm from the curved surfaces of the knee implant.
3) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein a strong permanent magnet is appropriately attached to a mu-metal cylindrical fixture with the help of Allen bolts.
4) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 which is rotated at an optimum rotational speed through a CNC milling machine head.
5) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein CNC controller controls the custom-made 4th axis spindle chuck (2a).
6) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein custom-made 4th axis spindle chuck (2a) is externally connected to a 3-axis CNC milling machine bed.
7) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein the Carbonyl iron particles ( CIPs ) in magnetorheological (MR) fluid is of 40 volume %.
8) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein the diamond abrasive particles in magnetorheological (MR) fluid is 7.1 volume %.
9) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein glycerol in the magnetorheological (MR) fluid is 8 volume % and hydrogen peroxide (H2O2) is 1.3 volume % and deionized water is 43.6 %.
10) The polishing tool arrangement for uniform polishing the knee implant as claimed in claim 1 wherein the brass tool support (9), is tightly attached to magnet fixture (3).