WO2022097009A1

WO2022097009A1 - Backup pad

Info

Publication number: WO2022097009A1
Application number: PCT/IB2021/060096
Authority: WO
Inventors: Samad JAVID; Jonathan B. Arthur; Justin A. Riddle; Joseph B. FARLEY; Brett R. HEMES; Thomas J. STREY
Original assignee: 3M Innovative Properties Company
Priority date: 2020-11-06
Filing date: 2021-11-01
Publication date: 2022-05-12
Also published as: JP2023547216A; EP4240559A1; US20240017377A1; KR20230097115A

Abstract

A method of tuning the contact pressure across an abrasive disc is presented. The method includes coupling the abrasive disc to a backup pad comprising a pressure tuning feature that causes an experienced pressure by a worksurface, across a radius of the abrasive disc, to be uniform. The method also includes abrading a worksurface by contacting the abrasive disc to the worksurface. The backup pad causes the abrasive disc to have a cut rate that is substantially uniform across the surface of the abrasive disc when compared to the abrasive disc on a backup pad with no pressure tuning feature.

Description

BACKUP PAD

BACKGROUND

Abrasive fiber discs typically have an abrasive layer on a vulcanized fiber backing. In one common use, an abrasive fiber disc is mounted to a backup pad that is driven by a rotating power shaft of an angle grinder. The backup pad allows the operator to exert pressure toward a worksurface being abraded while mitigating pressure, angle and surface variation. Some such backup pads have raised ridges that can increase pressure and provide channels for escaping debris against a worksurface being abraded compared to adjacent portions of the disc, resulting in increased abrading rate. When abrasive discs are worn out and changed, they are removed from a backup pad, which can often be reused several times prior to being discarded.

SUMMARY

A method of managing the contact pressure across an abrasive disc is presented. The method includes coupling the abrasive disc to a backup pad comprising a pressure tuning feature that causes an experienced pressure by a worksurface, across a radius of the abrasive disc, to be uniform. The method also includes abrading a worksurface by contacting the abrasive disc to the worksurface. The backup pad causes the abrasive disc to have a cut rate that is substantially uniform across the surface of the abrasive disc when compared to the abrasive disc on a backup pad with no pressure tuning feature.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

FIGS 1 A- 1C illustrate an abrasive disc assembly mounted on a drive shaft of a power tool and parameters related thereto.

FIGS. 2A-2E illustrate an abrasive disc mounting assembly with a nonuniform thickness pressure tuning feature.

FIGS. 3A-3B illustrate an abrasive disc mounting assembly with a concentric ring pressure tuning feature. FIGS. 4A-4C illustrates an abrasive disc mounting assembly with a nonuniform surface.

FIG. 5 illustrates a method of providing a uniform cut rate in accordance with embodiments herein.

FIG. 6 is a robotic paint repair schematic in which embodiments of the present invention are useful.

FIG. 7 illustrates an exploded view of the components of a robotic paint repair stack.

FIGS. 8A-8B illustrate a tool for a robotic abrasive operation and a corresponding pressure profile.

FIGS. 9A-9G illustrate tools for providing a patterned cut rate with a robotic repair unit in accordance with embodiments herein.

FIG. 10 illustrates a method of providing a patterned cut rate with a robotic abrading system in accordance with embodiments herein.

FIGS. 11-14 relate to Example and Comparative Example constructions and results discussed in greater detail in the Example section below.

DETAILED DESCRIPTION

In this application, the terms “compressible” or “incompressible” refers to a material property, i.e., compressibility, of an object (e.g., an elastomer outer layer) which is a measure of the relative volume change of the material in response to a pressure. For example, the term “substantially incompressible” refers to a material having a Poisson’s ratio greater than about 0.45.

The term “elastically deformable” refers to a deformed object (e.g., an inner layer of synthetic foam) being capable of substantially 100% (e.g., 99% or more, 99.5% or more, or 99.9% or more) recovering to its original, undeformed state.

In this application, the terms “polymer” or “polymers” includes homopolymers and copolymers, as well as homopolymers or copolymers that may be formed in a miscible blend, e.g., by coextrusion or by reaction, including, e.g., transesterification. The term “copolymer” includes random, block and star (e.g. dendritic) copolymers.

The term “pressure tuning feature” as used herein refers to a component of an abrasive backup pad assembly. This feature is mounted permanently or temporarily on a side of a hard backup component of the assembly, opposite to a spindle on the other side of the hard backup component which is used to connect the assembly to a power tool. An abrasive disc is mounted on the free surface of the “pressure tuning feature” apart from the hard backup component in an abrasive process. The “pressure tuning feature” is substantially softer than the hard backup component of the assembly and thus it experiences substantial deformation compared to the hard backup component when the assembly is engaged to a worksurface in an abrasive process. The main roles of the “pressure tuning feature” in an abrasive backup pad assembly during an abrasive process includes, but is not limited to, distributing contact pressure uniformly between the pad assembly and a desired portion of the worksurface where material is supposed to be removed from, dampening the contact pressure variation caused by disturbances such as irregularities in the worksurface, inhomogeneities in the abrasive disc, vibration of the abrasive power tool, as well as heat and debris management.

In this application, the terms “about” or “approximately” with reference to a numerical value or a shape means +/- five percent of the numerical value or property or characteristic, but expressly includes the exact numerical value. For example, an elastic modulus of “about” 200 psi refers to an elastic modulus from 190 to 210 psi, but also expressly includes an elastic modulus of exactly 200 psi.

In this application, the term “substantially” with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited. For example, a substrate (e.g., web) that is “substantially” transparent refers to a substrate (e.g., web) that transmits more radiation (e.g. visible light) than it fails to transmit (e.g. absorbs and reflects). Thus, a substrate (e.g., web) that transmits more than 50% of the visible light incident upon its surface is substantially transparent, but a substrate (e.g., web) that transmits 50% or less of the visible light incident upon its surface is not substantially transparent.

Referring now to FIGS. 1A and IB, a typical abrasive disc mounting assembly 100 comprises a backup pad 110 and a clamp assembly 140 that secures an abrasive disc 20. The connection can be threaded, keyed, bolted, friction or any number of suitable fastener options known to those in the art. An abrasive disc mounting assembly 100 includes an outwardly facing centrally disposed fastening member 130 (shown as a threaded bore, see FIG. 4) that is adapted to engage a threaded drive shaft 10 of a power tool (not shown) such as, for example, an angle grinder. The backup pad 110 may have ribbed projections on a disc- engaging surface that provide added support to abrasive disc 20. During abrading of a worksurface, the drive shaft 10 rotates around a rotational axis of use (115).

Because abrasive disc 20 spins in direction 30 during an abrading operation, as illustrated in FIG. 1C, both a linear velocity profile 40 and a material removal rate profile 50 (assuming constant applied pressure between abrasive disc 20 and a worksurface) show a higher linear velocity, and a higher removal rate as a distance from the disc center increases. This causes uneven cut rate across the surface of abrasive disc 20 increasing from the disc center toward the disc perimeter. Additionally, the wear on abrasive disc 20 is uneven, with faster wear occurring on the exterior and as the abrasive disc wears down, it causes still more uneven cut rate across the surface of the abrasive disc. For human-operated abrasive operations, it is often desired to have a uniform cut rate along a radius extending from a center to an edge of an abrasive disc. However, it is expressly contemplated that, for some abrasive operations it may be desired to have a patterned cut rate other than uniform. While the embodiments discussed in FIGS. 2-7 are directed towards achieving a patterned cut rate that is uniform across a surface of an abrasive disc 20, it is expressly contemplated that one having skill in the art could adapt them to result in an uneven or other patterned cut rate. For example, a patterned cut rate may be useful for managing debris removal, heat generation, blending of cut rate, feathering a cut rate, reduction in secondary scratching and haze avoidance.

FIGS. 1A and IB illustrate a cone-shaped backup pad 110. However, it is expressly contemplated that other backup pad designs may also benefit from the embodiments discussed herein. For example, FIGS. 3A-3B illustrate a flat backup pad 304. Different backup pad designs and construction may be useful for different applications. For example, a cone design may be useful for volume displacement when significant material is being removed or added. Additionally, different material construction may be important for the compressibility or flexibility needs of a given application.

FIGS. 2A-2E illustrate an abrasive disc mounting assembly with a nonuniform thickness pressure tuning feature. FIG. 2A is a perspective view of assembly 200, which includes a spindle 210 coupled to a conical backup pad 220, which in turn is coupled to a pressure tuning feature 230 with a conical shape cavity, which substantially matches the conical backup pad 220, on a first side. Pressure tuning feature 230 couples to the backup pad 220 on a first side and, on an opposite side 240, receives an abrasive disc. Abrasive-receiving side 240 is, in some embodiments, substantially flat, as illustrated in FIGS. 2B and 2C. FIG. 2B illustrates a side view 225 of assembly 200. FIG. 2C illustrates a cutaway view 250 of assembly 200 along section line 2C-2C illustrated in FIG. 2B. As illustrated, pressure tuning feature 230 substantially equalizes a depth 224 of the backup pad 220 along a width 222 of assembly 200.

FIG. 2D illustrates a graph of contact pressure along a radius of a backup pad designed like that of FIG. 2C against a worksurface. As illustrated, the contact pressure decreases along the radius of the backup pad from disc center toward its perimeter.

FIG. 2E illustrates an example relative composition of the backup pad 280 and the pressure tuning feature 290, for example as a cutaway view similar to the view 250. As a relative portion of height 294 corresponding to the pressure tuning feature 290 decreases, the relative portion of the backup pad 280 increases. In some embodiments, the pressure tuning feature 290 is at least a portion of depth 294 along the entire radius 272. In some embodiments, surface 284 of pressure tuning feature 290 is straight. An abrasive disc 286 can be mounted on surface 284 of pressure tuning feature 290. In some embodiments, interface 282 between backup pad 280 and pressure tuning feature 290, at any point along radius 272, is straight with a constant slope. The slope of interface 282 can be selected based on a desired profde for contact pressure on abrasive disc 286 along radius 272 when the pad assembly 270 is compressed against a worksurface in an abrasive process. Even though it is not illustrated in FIG 2E, in some embodiments pad assembly 270 can include channels extended between surface 284 of pressure tuning feature 290, where an abrasive disc is mounted, and the opposite surface of the assembly on backup pad 280 for dust and debris extraction.

The exact composition and hardness of pressure tuning feature 290 can vary based on a desired contact pressure profile between abrasive disc 286 and a worksurface during an abrasive process. Lower contact pressures can be obtained by using a softer material. Also, more variation in the thickness of pressure tuning feature 290 across the pad radius causes more variation in contact pressure across the pad which might be required to obtain a desired cut profile.

Components of both backup pad 280 and pressure tuning feature 290 should be made of appropriately durable materials. Examples of materials for backup pad 280 include engineering plastics (e.g., nylons, polyphenylene sulfide, polyether ketone, polyether ether ketone, polycarbonate, high density polyethylene, high density polypropylene, polyester, polyurethane, etc.), polymer composites, metals, ceramic composites, and combinations thereof.

The material used for pressure tuning feature 290 may be substantially softer than the material used for backup pad 280. This softness may be provided in several ways, for example by choosing a material with a lower hardness (as indicated using any appropriate hardness scale, such as Shore A or Shore OO), by choosing a material with a lower elastic modulus, by choosing a material with a higher compressibility (typically quantified via a material’s Poisson’s ratio), or by modifying the structure of the softer material to contain a plurality of gas inclusions, such as a foam or an engraved structure, etc. In some embodiments, the pressure tuning feature 290 can include a material having a hardness of less than about 50 Shore A, less than about 40 Shore A, and optionally less than about 40 Shore A (as measured using ASTM D2240). In some embodiments, the materials used in the pressure tuning feature 290 may have an elastic modulus of less than about 500 psi, less than about 400 psi, or optionally less than about 200 psi. In some embodiments, the compressibility of the pressure tuning feature 290 may be measured via Compression Force Deflection Testing per ASTM D3574 when the pressure tuning feature is foam; and via Compression-Deflection Testing per ASTM D1056 when the pressure tuning feature is a flexible cellular material such as, for example, sponge or expandable rubber. The pressure tuning feature 290 may have a compressibility of less than about 60 psi at 25% deflection, optionally less than about 45 psi at 25% deflection. The pressure tuning feature 290 is configured to be elastically deformable, e.g., being capable of substantially 100% (e.g., 99% or more, 99.5% or more, or 99.9% or more) recovering to its original state after being deformed. In some embodiments, the pressure tuning feature 290 can be compressible (i.e. having a Poisson’s ratio of less than 0.2 or less than 0.1) to provide the desired deformability. In some embodiments, the pressure tuning feature 290 may be substantially incompressible, e.g., the relative volume change of the material in response to a contact pressure is less than 5%, less than 2%, less than 1%, less than 0.5%, or less than 0.2%, but sufficiently soft to provide the desired deformability. In some embodiments, the pressure tuning feature 290 may be a made of a substantially incompressible material which has been patterned, 3D printed, embossed, or engraved to provide the desired deformability. In some embodiments, the pressure tuning feature 290 can have a Poisson’s ratio less than about 0.5, less than about 0.4, less than about 0.3, or preferably less than about 0.2. In some embodiments, the pressure tuning feature 290 can have a negative Poisson’s ratio. In some embodiments, the pressure tuning feature 290 can include one or more materials of a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric or nonwoven layer, or a soft rubber. A suitable foam can be open-celled or closed-celled, including, for example, synthetic or natural foams, thermoformed foams, polyurethanes, polyesters, polyethers, filled or grafted polyethers, viscoelastic foams, melamine foam, polyethylenes, cross-linked polyethylenes, polypropylenes, silicone, ionomeric foams, etc. The pressure tuning feature 290 may also include foamed elastomers or vulcanized rubbers, including, for example, isoprene, neoprene, polybutadiene, polyisoprene, polychloroprene, nitrile rubbers, polyvinyl chloride and nitrile rubber, ethylene -propylene copolymers such as EPDM (ethylene propylene diene monomer), and butyl rubber (e.g., isobutylene-isoprene copolymer). A suitable foam pressure tuning feature 290 can have a compressibility, for example, less than about 60 psi at 25% deflection, or less than about 45 psi at 25% deflection. It is to be understood that the pressure tuning feature 290 may include any suitable compressible structures such as, for example, springs, nonwovens, fabrics, air bladders, etc. In some pressure tuning feature 290 can be 3D printed to provide desired Poisson’s ratio, compressibility, and elastic response.

Additionally, while a single pressure tuning feature 290 is illustrated, it is expressly contemplated that feature 290 may be made of multiple layers and / or multiple materials in a layered or agglomerate construction.

FIGS. 3A-3B illustrate an abrasive disc mounting assembly with a concentric ring pressure tuning feature. FIGS. 3 A and 3B illustrate different perspective views of assembly 300, which includes a spindle 302, backup pad 304, and pressure tuning feature 350. As illustrated in FIG 3A, the pressure tuning feature includes multiple concentric rings. While three rings 310, 320 and 330 are illustrated in FIG. 3A, it is expressly contemplated that, in other embodiments, only two rings are present, or more rings, such as four, five, six, eight, ten, or even more, are present.

In one embodiment, as illustrated in FIG. 3 A, of an overall radius 306, each ring 310, 320, 330 occupies an equal portion, each having an equal radial depth 312, 322, 332 across pressure tuning feature 350. The pressure tuning feature 350 can also be a single piece with gradual or stepwise hardness change from the center to the edge of the pad. Using an adhesive layer, a hook-and-loop mounting system, or another suitable appropriate mounting system, an abrasive disc can be mounted on the surface of the pressure tuning feature 350 away from the backup pad 304 in abrasive applications. One advantage of the assembly 300 is that the variation of the stiffness or hardness from the center to the edge of the pressure tuning feature 350 can be adjusted to account for the linear velocity variation across the pad, as indicated by element 40 in FIG. 1C, and provide a uniform cut rate across the pad in abrasive or polishing applications.

Each of rings 310, 320 and 330, in one embodiment, vary in their material properties. In one embodiment, rings increase in material softness as a radial distance from the center increases. Each ring may be made of a different material than an adjoining ring, such that the softness of adjacent rings increases from the center to the exterior of the backup pad.

This softness may be provided in several ways, for example by choosing a material with a lower hardness (as indicated using any appropriate hardness scale, such as Shore D, Shore A or Shore OO), by choosing a material with a lower elastic modulus, by choosing a material with a higher compressibility (typically quantified via a material’s Poisson’s ratio), or by modifying the structure of the softer material to contain a plurality of gas inclusions, such as a foam or an engraved structure, etc. For example, when ring 330 and 320 in the assembly 300 include materials having a hardness of 60 and 40 Shore A (as measured using ASTM D2240) respectively, then the hardness of rings 310 may be less than 40 Shore A. It should be noted that in some cases the hardness may be most appropriately measured using different scales for pressure tuning feature 350 (e.g., Shore A or Shore OO). In some embodiments, the compressibility of the materials used in pressure tuning feature 350 may be measured via Compression Force Deflection Testing per ASTM D3574 when the material is foam; and via Compression-Deflection Testing per ASTM DI 056 when the material is a flexible cellular material such as, for example, sponge or expandable rubber. The materials used to the pressure tuning feature 350 may have an elastic modulus of less than about 650 psi, less than about 500 psi, or optionally less than about 400 psi. The pressure tuning feature 350 may include materials with a compressibility in the range of 10 to 170 psi at 25% deflection. The pressure tuning feature 350 is configured to be elastically deformable, e.g., being capable of substantially 100% (e.g., 99% or more, 99.5% or more, or 99.9% or more) recovering to its original state after being deformed. In some embodiments, some materials used in the pressure tuning feature 350 can be compressible (i.e. having a Poisson’s ratio of less than 0.2 or less than 0.1) to provide the desired deformability. In some embodiments, some materials used in pressure tuning feature 350 may be substantially incompressible, e.g., the relative volume change of the material in response to a contact pressure is less than 5%, less than 2%, less than 1%, less than 0.5%, or less than 0.2%, but sufficiently soft to provide the desired deformability. In some embodiments, some materials used in the pressure tuning feature 350 may be made of a substantially incompressible material which has been patterned, 3D printed, embossed, or engraved to provide the desired deformability.

In some embodiments, the pressure tuning feature 350 can include materials with a hardness of less than about 60 Shore A, less than about 40 Shore A, or even less than about 30 Shore A. In some embodiments, the materials used in the pressure tuning feature 350 can have a Poisson’s ratio less than about 0.5, less than about 0.4, less than about 0.3, or even less than about 0.2. In some embodiments, some of the materials used in the pressure tuning feature 350 can have a negative Poisson’s ratio.

In some embodiments, the pressure tuning feature 350 can include one or more materials of a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric or nonwoven layer, or a soft rubber. A suitable foam can be open-celled or closed-celled, including, for example, synthetic or natural foams, thermoformed foams, polyurethanes, polyesters, polyethers, filled or grafted polyethers, viscoelastic foams, melamine foam, polyethylenes, cross-linked polyethylenes, polypropylenes, silicone, ionomeric foams, etc. The pressure tuning feature 350 may also include foamed elastomers or vulcanized rubbers, including, for example, isoprene, neoprene, polybutadiene, polyisoprene, polychloroprene, nitrile rubbers, polyvinyl chloride and nitrile rubber, ethylene -propylene copolymers such as EPDM (ethylene propylene diene monomer), and butyl rubber (e.g., isobutylene-isoprene copolymer). It is to be understood that the pressure tuning feature 350 may include any suitable compressible structures such as, for example, springs, nonwovens, fabrics, air bladders, etc. In some embodiments, at least a portion of the pressure tuning feature 350 can be 3D printed to provide desired Poisson’s ratio, compressibility, and elastic response.

The backup pad 304 is substantially harder than the pressure tuning feature 350, i.e. when the assembly 300 is used in an abrasive application, the compressive deformation of the backup pad 304 is negligible compared to that of the pressure tuning feature 350. Components of both backup pad 304 and pressure tuning feature 350 should be made of appropriately durable materials. Examples of materials for backup pad 304 include engineering plastics (e.g., nylons, polyphenylene sulfide, polyether ketone, polyether ether ketone, polycarbonate, high density polyethylene, high density polypropylene, polyester, polyurethane, etc.), polymer composites, metals, ceramic composites, and combinations thereof.

FIGS. 4A-4C illustrates an abrasive disc mounting assembly with a nonuniform surface . Assembly 400 includes a spindle 410, which connects to a drive shaft of a power tool or machine. A conical backup pad 420 is connected to spindle 410 from its flat surface 450. A pressure tuning feature 430 is mounted on the conical side, on the opposite side of the surface 450, of the backup pad 420. In one embodiment, the thickness of the pressure tuning feature 430 is uniform across the conical backup pad. An abrasive pad can be mounted on surface 440 of the pressure tuning feature 430 using an adhesive layer, a hook-and-loop mounting system, or other appropriate mounting systems for abrasive applications. FIG. 4A illustrates a side view of assembly 400. FIG. 4B illustrates a cutaway view of assembly 400, taken along section line4B-4B illustrated in FIG. 4A. FIG. 4C illustrates an exploded view of assembly 400. In one embodiment, the backup pad 420 can be made of a flat piece 460 and a conical piece 436. Assembly 400 has an overall diameter 402. In some embodiments, pressure tuning feature 430 has a diameter 432 that is substantially the same length as diameter 402. However, in some embodiments, diameter 432 is shorter than diameter 402. The conical backup pad 420 has a grade 434, which may be adjusted to tune the contact pressure between an abrasive pad mounted on the surface 440 of the pressure tuning feature 430 and a worksurface when the abrasive pad on the assembly 400 meets the worksurface in an abrasive operation.. The grade 434 is less than 180°. It can be, for example about 175°, about 170°, about 165°, about 160°, about 155°, about 150°, about 145°, about 140° or about 135°. Additionally, the grade may be shallower, for example between about 176° and 179°.

In some embodiments, an abrasive pad on the mounting assembly 400 first comes to contact with a worksurface with the tip of its conical portion. By engaging the pad more against the worksurface, the other portions of the abrasive pad meet then the worksurface to abrade that. In this scenario, the pressure tuning feature 430 is compressed more near the conical tip and its compression decreases toward the edge of the pad. This leads to a contact pressure profile which is maximum in the center of the pad and decreases across the pad toward its edge . This decreasing contact pressure can account for the increasing linear velocity profile 40 illustrated in FIG 1C and consequently help the pad to remove uniform material across the pad from its center toward its edge

In another embodiment where the goal is to abrade a small portion of a worksurface, a pad on the mounting assembly 400 provides this capability to only contact the desired area of the worksurface without contacting other portions of that. This capability gives also the opportunity of using different locations of the pad to abrade the worksurface which leads to a longer life for the abrasive pad compared to a traditional pad assembly with a flat surface which is used mostly from areas close to its edge.

The material used for pressure tuning feature 430 is substantially softer than the material used for conical backup pad 420, i.e. when the assembly 400 is used in an abrasive application, the compressive deformation of the backup pad 420 is negligible compared to that of the pressure tuning feature 430. The softness may be provided in several ways, for example by choosing a material with a lower hardness (as indicated using any appropriate hardness scale, such as Shore A or Shore OO), by choosing a material with a lower elastic modulus, by choosing a material with a higher compressibility (typically quantified via a material’s Poisson’s ratio), or by modifying the structure of the softer material to contain a plurality of gas inclusions, such as a foam or an engraved structure, etc. In some embodiments, the compressibility of the pressure tuning feature 430 may be measured via Compression Force Deflection Testing per ASTM D3574 when the pressure tuning feature is foam; and via Compression-Deflection Testing per ASTM DI 056 when the compressible is a flexible cellular material such as, for example, sponge or expandable rubber. The pressure tuning feature 430 may have a hardness of less than about 60 Shore A, less than about 50 Shore A, and preferably less than about 40 Shore A. The material used to the pressure tuning feature 430 may have an elastic modulus of less than about 400 psi, less than about 300 psi, and preferably less than about 200 psi. The pressure tuning feature 430 may have a compressibility of less than about 75 psi at 25% deflection, optionally less than about 45 psi at 25% deflection. The pressure tuning feature 430 is configured to be elastically deformable, e.g., being capable of substantially 100% (e.g., 99% or more, 99.5% or more, or 99.9% or more) recovering to its original state after being deformed. In some embodiments, the pressure tuning feature 430 can be compressible (i.e. having a Poisson’s ratio of less than 0.2 or less than 0. 1) to provide the desired deformability. In some embodiments, the pressure tuning feature 430 may be substantially incompressible, e.g., the relative volume change of the material in response to a contact pressure is less than 5%, less than 2%, less than 1%, less than 0.5%, or less than 0.2%, but sufficiently soft to provide the desired deformability. In some embodiments, pressure tuning feature 430 may be a made of a substantially incompressible material which has been patterned, 3D printed, embossed, or engraved to provide the desired deformability. In some embodiments, the pressure tuning feature 430 can include one or more materials of a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric or nonwoven layer, or a soft rubber. A suitable foam can be open-celled or closed-celled, including, for example, synthetic or natural foams, thermoformed foams, polyurethanes, polyesters, polyethers, filled or grafted polyethers, viscoelastic foams, melamine foam, polyethylenes, cross-linked polyethylenes, polypropylenes, silicone, ionomeric foams, etc. The pressure tuning feature 430 may also include foamed elastomers or vulcanized rubbers, including, for example, isoprene, neoprene, polybutadiene, polyisoprene, polychloroprene, nitrile rubbers, polyvinyl chloride and nitrile rubber, ethylene -propylene copolymers such as EPDM (ethylene propylene diene monomer), and butyl rubber (e.g., isobutylene-isoprene copolymer). A suitable foam pressure tuning feature 430 can have a compressibility, for example, less than about 75 psi at 25% deflection, optionally less than about 45 psi at 25% deflection. It is to be understood that the pressure tuning feature 430 may include any suitable compressible structures such as, for example, springs, nonwovens, fabrics, air bladders, etc. In some embodiments, the pressure tuning feature 430 can be 3D printed to provide desired Poisson’s ratio, compressibility, and elastic response.

Components of both backup pad 420 and pressure tuning feature 430 should be made of appropriately durable materials. Examples of materials for backup pad 420 include engineering plastics (e.g., nylons, polyphenylene sulfide, polyether ketone, polyether ether ketone, polycarbonate, high density polyethylene, high density polypropylene, polyester, polyurethane, etc.), polymer composites, metals, ceramic composites, and combinations thereof.

The embodiments illustrated in FIGS. 2-4 are designed to achieve a patterned cut rate that is uniform across the diameter of a backup pad. This increases the overall efficiency and service life of each individual abrasive pad attached to the backup pad. These embodiments also provide a more uniform cut and surface finish on worksurfaces being abraded by them compared to traditional pad assemblies. Each embodiment illustrated in FIGS. 2-4 are exemplary. It is expressly contemplated that each can be customized depending on a given abrading operation’s requirement. For example, through channels may be extended from the surface of the mounting systems exposed to the abrasive pad to the free surface of the backup pad in each embodiment to ease debris and dust extraction and management during abrasive applications. Additionally, each embodiment provides unique advantages. FIG. 5 illustrates a method of providing a uniform cut rate in accordance with embodiments herein. Method 500 may be useful with any of the abrasive disc mounting assemblies of FIGS. 2-4, or with another suitable abrasive disc mounting design.

In block 510, an abrasive disc mounting assembly I is coupled to a tool. The tool can be a linear sander, rotary sander, orbital sander, random orbital sander or other suitable tools. The abrasive disc mounting assembly may have, on a side opposing a tool connection side, a flat surface 502, a conical surface 504, or another surface structure 506, such as a truncated cone.

In block 520, an abrasive pad is coupled to an abrasive disc mounting assembly that includes a backup pad coupled to a pressure tuning feature. The abrasive pad may be coupled directly to the pressure tuning feature, as illustrated in block 522, or directly to a backup pad, as illustrated in block 524. The abrasive pad may also be coupled to the assembly in another suitable manner, as indicated in block 526.

In block 530, an abrading operation is conducted. This may include actuating a tool manually, as illustrated in block 527, semi-manually, as illustrated in block 528, or by other suitable methods, such as a robot, as illustrated in block 529.

FIG. 6 is a robotic paint repair schematic in which embodiments of the present invention are useful. While the example of a paint repair robot 604 is illustrated in FIG. 6, it is expressly contemplated that the tool and backup pad embodiments illustrated in FIGS. 2-5 and 8-10 could be used for applications other than paint repair.

In FIG. 6, the respective boxes represent various hardware components of the system including robot controller 602, robot manipulator 604, and robotic paint repair stack 606 including compliant force control unit 608, tool 610, and abrasive articles/compounds 612. The flow of data is depicted by the background arrow 614 which starts with pre-inspection data module 616 that provides inspection data including identified defects in the substrate and ends with post-inspection defect data module 618 for processing data generated from the substrate 620 during the defect repair process.

In operation, the defect locations and characteristics are fed from the pre-inspection data module 616 to the robot controller 602 that controls robot manipulator 604 on which a program guides an end effector (stack) 606 to the identified defect to execute some predetermined repair program (deterministic) policy. In some rare cases, the policy might be able to adapt depending on the provided defect characteristics. For paint repair applications, the robotic paint repair stack 606 comprises abrasive tooling 610 and abrasive articles and compounds 612 along with any ancillary equipment such as (compliant) force control unit 608. As used herein, the robotic paint repair stack 606 is more or less synonymous with the term end effector; however, in this document the term “stack” is the end effector in the context of robotic paint repair. Also, though described for providing robotic paint repair, which includes repair of primer, paint, and clear coats, it will be appreciated that the techniques described herein lend themselves to other industrial applications beyond paint repair.

The stack 606, in FIG. 6, can provide feedback back to controller 602, in a feedback loop, such that operation of robot 604, compliance force control unit 608 and tool 610 can continuously adjust settings during an abrasive situation.

FIG. 7 illustrates an exploded view of the components of a robotic paint repair stack. As illustrated, the robotic paint repair stack 606 comprises a robot arm 700, force control sensors and devices 608, a grinding/polishing tool 610, a hardware integration device 702, abrasive pad(s) and compounds 612, a design abrasives process 704, and data and services 706. These elements may work together to identify defect locations and to implement a predetermined repair program using a deterministic policy for the identified defect, such as the policy discussed in co-owned and co-pending PCT Application No. PCT/IB2019/057053, filed on August 21, 2019.

FIGS. 8A-8B illustrate a tool for a robotic abrasive operation and a corresponding contact pressure profile of the tool against a worksurface.

FIG. 8A illustrates a tool 800 for a robotic grinding unit. Tool 800 is connected to a rotary device via the vertical shaft 810. An abrasive article attaches to tool 800 on a surface of backup pad 820, on opposite side of shaft 810 backup pad 820. Backup pad 820 is often a flexible pad. FIG. 8B illustrates a contact pressure profile 850 that results from the tool being used against a worksurface. Even with the flexibility of the pad, the pressure profile 850 of the abrasive on the surface is irregular. As the pressure is measured from the center of the abrasive tool 800, at approximately 9mm from the center to 13mm on the radius, there is a spike in pressure.

FIG. 8A illustrates a rigid bed design for tool 800, which includes a foam pad that provides flexibility for an abrasive article, connected by adhesive, hook-and-loop or mechanically, to conform to the surface within the pressure profile of the backing foam. Buildup of detritus often occurs as the tool 800 engages a work surface. This, as well as the characteristics of the tool during high velocity abrading, contributes to the lack of uniformity in pressure.

FIGS. 9A-9G illustrate tools for providing a patterned cut rate with a robotic repair unit in accordance with embodiments herein. FIGS. 9A-9C illustrate embodiments of tools that can directly engage a robotic, for example using a force control unit and / or end effector in some embodiments.

Handheld power tools require that the tool accommodate the lack of motor precision inherent in a human user. However, embodiments of tools illustrated in FIGS. 9A-9C are useful for robotic units able to leverage the precision and accuracy of automated abrasive tooling.

Tool 900 engages a robotic unit using shaft 902. Tool has a pad engaging surface 910 for engaging pad 904, which engages an abrasive article. Tool surface 910 can be modified to include a pattern of apertures, illustrated in FIG. 9A as including two sizes of holes 912 and 914. As illustrated in FIG. 9A, holes 912, 914 extend through surface 910. Hole sets 912 and 914 are arranged about shaft 902, with smaller holes 912 closer to the shaft than larger holes 914. In some embodiments, each hole in a given set of holes 912, 914 is equally spaced from adjacent, similarly sized holes. Additionally, while circular holes are illustrated in FIG. 9A, it is expressly contemplated that slats extending partly or completely through surface 910, indentations extending partway through surface 910, or another suitable modification that allows for flexing of surface 910 are envisioned. Specifically, the design of FIG. 9A allows tool 800 to flex under speed and pressure to facilitate a ‘feathered edge’ when a paint defect is abraded, such that the surface modification is not readily detectable.

However, it is expressly contemplated that design of a given tool can facilitate specific effects (feathering, cutting edge) as well as to better manage detritus created during an abrading operation. The goal of managing cuttings is to reduce the creation of undesired surface artifacts as well as to increase abrasive disk life and cutting consistency.

FIG. 9B illustrates an angled tool 920 which includes a shaft 922 connected to an angled tool surface 930, which allows for the weakening of the contact points at the outer edges so that more force is applied at the center of the tool 920 and contact is weakened as the tool 900 is in contact farther out from the center of the tool.

FIG. 9C illustrates a tool 940 with a scalloped edge in addition to an angled surface. However, it is expressly contemplated that, in some embodiments, scalloped edge is present alone, without an angled surface. Tool 940 has a shaft 942, that connects to an angled tool surface 950 with a plurality of scallops 952 equally spaced about the circumference of tool surface 950. The scallops 952 further differentiate the force from the center of tool 940 to the edges as compared to tool 920.

FIG. 9D illustrates a robotic tool 962 with a foam pad 964 in an assembly 962.

FIG. 9E illustrates a flexible tool 972 with a foam pad 974 in an assembly 970. As illustrated in FIG. 9E, flexible tool has a grade 976 from the spindle to an edge of the tool, such that the edge of the tool is thinner than the center of the tool, resulting in added flexibility at the edges.

FIG. 9F illustrates a patterned tool 982 with a foam pad 982 in an assembly 980. As illustrated in FIG. 9F, tool 982 includes a plurality of indentations 985 extending inward from a circumference of tool 982. Indentations 985, are illustrated in FIG. 9F as having two edges 988 meeting at a point to form an angle 986. However, it is expressly contemplated that rounded edges and inflection points are possible. Indentation 985 has a depth 987 extending inward from a circumference of tool 982. Indentations 985 provide some pressure relief at the outside of tool assembly 980, which allows for better debris management at edge. Illustrated in FIG. 5F is an embodiment with four indentations spaced equidistant apart on the tool circumference. However, it is expressly contemplated that more, or fewer, indentations might be suitable in some embodiments. For example, only two indentations 985 could be present, or three indentations 985. Similarly, 5, 6, 7, 8, 10, 12, 16, 20 or more indentations 985 could be present.

FIG. 9G illustrates a patterned tool 992 with a foam pad 994 in an assembly 990. Tool 992 includes a plurality of cutaway portions 993 are present within tool 992. As illustrated in FIG. 9G, cutaway portions extend substantially from a circumference to a spindle radius of tool 992. Cutaway portions can be defined by a length 998, extending perpendicularly from the circumference, and a width 997. In some embodiments, width 997 is variable from a circumference to a spindle of tool 992, for example wider at the circumference than the spindle. In some embodiments, cutaways 993 have curvature 998 at the intersection of the cutaway 993 with tool a tool spindle. Cutaways 993 provide significant pressure relief for tool 992, allowing for improved debris management, heat management and patterning.

While FIGS. 9F and 9G illustrate a flat tool surface extending from a tool spindle, it is expressly contemplated that the indentations 985 or cutaways 993 could be combined, in other embodiments, with gradient 976 to provide additional flexibility.

FIG. 10 illustrates a method of providing a patterned cut rate with a robotic abrading system in accordance with embodiments herein. As discussed above, robotic abrading systems have the ability to abrade small areas (e.g. under 35 mm in area) with fine control. Once an abrading operation has begun, a robotic control unit can adjust grinding parameters in order to increase cut rate, cut efficiency, or improve aesthetics of a work surface following a repair. Tools discussed herein can be used to create a patterned cut rate, for example an angled cut rate where a tool is tilted during an abrading operation to cause one point of a contact area is cut deeper than another point. Other patterns for cut rates are also contemplated.

In block 1010, a robotic control cell is initiated. Initiation may include providing power to a robotic repair unit, moving it into position such that an abrasive article can engage a work surface. The abrasive article may be urged into contact with the work surface using a motive robot arm. Pressure may be exerted, on the abrasive article, using a force control unit.

In block 1020, an abrasive operation is conducted. In some embodiments, the abrasive operation follows a preset repair plan, for example selected based on a desired end state of the work surface engaged. In other embodiments, the abrasive operation follows a dynamic plan to achieve a desired outcome - e.g. desired final work surface state, desired cut shape, work surface resistance, etc.

In block 1030, feedback is received. For example, feedback may be received from robot control sensor units, servo tool motor sensor units and/or sensor units embedded directly in the tool. Vibration may be sensed by the a vision system analyzing movement of the tool during operation frame to frame.

In block 1040, a tool parameter is modified in-situ, such that the abrasive operation can continue. In some embodiments, the feedback is received and a modification is made without an abrasive tool breaking contact with a worksurface. However, in other embodiments the tool must disconnect from a surface in order for sensor readings to be captured and feedback provided.

Tool parameters that can be modified in response to feedback received include a contact pressure 1042 between a tool and a worksurface, a contact angle 144 of the tool with respect to the work surface, or another suitable parameter. For example, rotational velocity can be modified with respect to a tool, or a pattern of movement of the tool with respect to the work surface, or another suitable parameter.

Abrasive discs may couple to backup pads and / or dampeners described herein using any suitable non-permanent attachment mechanism. For example, an adhesive may be applied, including a pressure-sensitive adhesive, in one embodiment. A hook-and-loop attachment may also be used, with either the hook or the loop portion on the non-abrasive side of abrasive disc.

An abrasive disc, in one embodiment, is a coated abrasive disc including a backing with a plurality of abrasive grains embedded within a make coat and optionally coated with a size coat and / or a super-size coat. The backing substrate can be any of fabric, open-weave cloth, knitted fabric, porous cloth, loop materials, unsealed fabrics, open or closed cell foams, a nonwoven fabric, a spun fiber, a film, a perforated film or any other suitable backing material. A fabric backing may include cloth (e.g., cloth made from fibers or yams comprising polyester, nylon, silk, cotton, and/or rayon, which may be woven, knit or stitch bonded) or scrim. The abrasive grains may include shaped abrasive grains, crushed abrasive grains, or platey shaped abrasive grains. The size of the abrasive grains may be selected based on the aggressiveness of the repair operation to be completed. The abrasive disc may be a stiff or flexible abrasive disc.

The above-presented description and figures are intended by way of example only and are not intended to limit the illustrative embodiments in any way except as set forth in the appended claims. It is noted that various technical aspects of the various elements of the various exemplary embodiments that have been described above can be combined in numerous other ways, all of which are considered to be within the scope of the disclosure.

Accordingly, although exemplary embodiments have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible. Therefore, the disclosure is not limited to the above-described embodiments but may be modified within the scope of appended claims, along with their full scope of equivalents.

A method of managing the contact pressure across an abrasive disc is presented that includes coupling the abrasive disc to a backup pad. The backup pad includes a pressure tuning feature that causes an experienced pressure by a worksurface, across a radius of the abrasive disc, to be uniform. The method also includes abrading a worksurface by contacting the abrasive disc to the worksurface. The backup pad causes the abrasive disc to have a cut rate that is substantially uniform across the surface of the abrasive disc when compared to the abrasive disc on a backup pad with no pressure tuning feature.

The method may be implemented such that the pressure tuning feature is elastically deformable.

The method may be implemented such that the pressure tuning feature is positioned between the backup pad and the abrasive disc.

The method may be implemented such that the pressure tuning feature includes a material having a hardness of less than about 60 Shore A.

The method may be implemented such that the pressure tuning feature includes a material having a compressibility of less than about 170 psi at 25% deflection.

The method may be implemented such that the pressure tuning feature includes a material that is compressible.

The method may be implemented such that the pressure tuning feature includes a material that is substantially incompressible.

The method may be implemented such that the pressure tuning feature includes a substantially incompressible material which has been patterned, 3D printed, embossed, or engraved.

The method may be implemented such that the pressure tuning feature includes a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric layer, a nonwoven layer, or a soft rubber.

The method may be implemented such that the pressure tuning feature is made of multiple layers and / or multiple materials in a layered or agglomerate construction.

The method may be implemented such that the backup pad includes channels extended from the surface of the pressure tuning feature, where the abrasive disc is mounted, to the opposite side of the backup pad for dust and debris extraction.

The method may be implemented such that the pressure tuning feature includes a material having an elastic modulus of less than about 650 psi.

The method may be implemented such that the pressure tuning feature has a nonuniform thickness.

The method may be implemented such that the pressure tuning feature has a conical cavity mounted on a conical surface of the backup pad. The method may be implemented such that the hardness of the pressure tuning feature changes across the pad from its center toward its perimeter.

The method may be implemented such that the hardness of the pressure tuning feature changes gradually across the pad. The method may be implemented such that the hardness of the pressure tuning feature changes stepwise across the pad.

The method may be implemented such that the pressure tuning feature includes of concentric rings with different harnesses.

The method may be implemented such that the hardness of the pressure tuning feature decreases from the pad’s center toward its perimeter.

The method may be implemented such that the change in the hardness of the pressure tuning feature across the pad is proportional to distance from the center of the pad.

The method may be implemented such that the backup pad has a nonplanar surface where a pressure tuning feature with a uniform thickness is mounted on that surface. The method may be implemented such that the nonplanar surface of the backup pad is conical, hemispherical, or domed shape.

The method may be implemented such that the backup pad in combination with the pressure tuning feature causes the abrasive disc to have improved debris management compared to the abrasive disc on a backup pad with no pressure tuning feature.

The method may be implemented such that the backup pad in combination with the pressure tuning feature causes the abrasive disc to have improved heat management compared to the abrasive disc on a backup pad with no pressure tuning feature.

The method may be implemented such that the backup pad in combination with the pressure tuning feature causes the abrasive disc to have improved feature blending compared to the abrasive disc on a backup pad with no pressure tuning feature.

An abrading system that causes an abrasive disc to provide a patterned cut rate that includes a tool configured to drive movement of the abrasive disc. The system also includes a backup pad coupled to the tool. The system also includes a pattern feature. The pattern feature causes the abrasive disc to exhibit a patterned cut rate when the tool is actuated. The patterned cut rate is different from a cut rate exhibited by the abrasive disc attached to the backup pad and tool without the pattern feature. The system may be implemented such that the tool is a robotic tool. The pattern feature is integrated into the tool.

The system may be implemented such that the pattern feature is a backup pad engaging surface of the tool.

The system may be implemented such that the pattern feature is a plurality of apertures in the backup pad engaging surface of the tool.

The system may be implemented such that the plurality of apertures includes a first set of apertures and a second set of apertures.

The system may be implemented such that the first set of apertures are closer to an edge of the backup engaging surface of the tool than the second set of apertures.

The system may be implemented such that the first set of apertures have a first radius, the second set of apertures have a second radius, and the first radius is larger than the second aperture.

The system may be implemented such that the apertures extend completely through the backup pad engaging surface of the tool.

The system may be implemented such that the pattern feature is a backup pad engaging portion of the tool coupled to a spindle. The backup pad engaging portion is perpendicular to the spindle.

The system may be implemented such that the backup pad engaging portion has a backup pad engaging surface with a first diameter, and a spindle-engaging surface with a second diameter. The first diameter is larger than the second diameter.

The system may be implemented such that an exterior edge of the backup pad engaging portion is angled from the spindle-engaging surface to the backup pad engaging surface.

The system may be implemented such that the backup pad engaging surface includes a scalloped edge.

The system may be implemented such that the backup pad engaging portion includes a perimeter with a plurality of concave portions.

The system may be implemented such that the concave portions are equally spaced about a circumference.

The system may be implemented such that the pattern feature causes a backup pad engaging portion of the tool to flex during an abrading operation. The system may be implemented such that the tool is a spindle configured to engage a power tool.

The system may be implemented such that the pattern feature is coupled to both the tool, on a first side, and the backup pad, on a second side.

The system may be implemented such that the pattern feature includes a first portion and a second portion.

The system may be implemented such that the first portion and second portion are coplanar and coupled to both the tool and the backup pad.

The system may be implemented such that the first portion and the second portion include different materials.

The system may be implemented such that the first and second portions include compressible materials.

The system may be implemented such that the first and second portions include incompressible materials.

The system may be implemented such that the pattern feature includes a compressible, cone-shaped feature.

The system may be implemented such that the pattern feature is coupled to the backup pad, on a first side, and is configured to couple to an abrasive article, on a second side.

The system may be implemented such that a cut rate of the system is substantially uniform across a radius extending from a center of the backup pad to an edge of the backup pad.

The system may be implemented such that a cut rate of the system has a local maximum.

The system may be implemented such that the cut rate has at least two local maxima.

The system may be implemented such that the pattern feature is elastically deformable.

The system may be implemented such that the pattern feature is positioned between the backup pad and the abrasive disc.

The system may be implemented such that the pattern feature includes a material having a hardness of less than about 60 Shore A.

The system may be implemented such that the pattern feature includes a material having a compressibility of less than about 170 psi at 25% deflection. The system may be implemented such that the pattern feature includes a material made of a substantially incompressible material which has been patterned, 3D printed, embossed, or engraved.

The system may be implemented such that the pattern feature includes a material that is compressible.

The system may be implemented such that the pattern feature includes one or more materials of a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric layer, a nonwoven layer, or a soft rubber.

The system may be implemented such that the pattern feature is made of multiple layers or multiple materials in a layered or agglomerate construction.

The system may be implemented such that the backup pad includes channels extending from the surface of the damping feature to the opposite side of the backup pad.

The system may be implemented such that the pattern feature includes a material having an elastic modulus of less than about 650 psi.

The system may be implemented such that the pattern feature has a nonuniform thickness.

The system may be implemented such that the pattern feature has a conical cavity mounted on a conical surface of the backup pad.

The system may be implemented such that the hardness of the pattern feature changes across the backup pad from a center to a perimeter.

The system may be implemented such that the hardness of the pattern feature changes gradually across the backup pad.

The system may be implemented such that the hardness of the pattern feature changes stepwise across the backup pad.

The system may be implemented such that the pattern feature includes a plurality of concentric rings, each concentric ring having a different hardness.

The system may be implemented such that the hardness of the pattern feature decreases from a center to a perimeter.

The system may be implemented such that the change in the hardness of the pattern feature across the backup pad is proportional to a distance from the center.

The system may be implemented such that the backup pad has a nonplanar surface. The pattern feature is mounted to the nonplanar surface. The system may be implemented such that the nonplanar surface of the backup pad is conical, hemispherical, or domed shape.

A backup pad for an abrasive system is presented that includes a tool engaging feature. The backup pad also includes an abrasive article engaging feature. The backup pad also includes a compressible feature that changes a cut rate profile of an abrasive article attached to the abrasive article engaging feature.

The backup pad may be implemented such that the tool engaging feature is on a first side of the backup pad and the abrasive article engaging feature is on a second side of the backup pad. The first side opposes the second side.

The backup pad may be implemented such that the compressible feature is elastically deformable.

The backup pad may be implemented such that the compressible feature is positioned between the backup pad and the abrasive disc.

The backup pad may be implemented such that the compressible feature includes a material having a hardness of less than about 60 Shore A.

The backup pad may be implemented such that the compressible feature includes a material having a compressibility of less than about 170 psi at 25% deflection.

The backup pad may be implemented such that the compressible feature includes a material which has been patterned, 3D printed, embossed, or engraved to provide the desired deformability.

The backup pad may be implemented such that the compressible feature includes a material that is compressible.

The backup pad may be implemented such that the compressible feature includes a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric or nonwoven layer, or a soft rubber.

The backup pad may be implemented such that the compressible feature is made of multiple layers and / or multiple materials in a layered or agglomerate construction.

The backup pad may be implemented such that the backup pad includes channels extended from a surface of the damping feature to the opposite side of the backup pad for dust and debris extraction.

The backup pad may be implemented such that the compressible feature includes a material having an elastic modulus of less than about 650 psi. The backup pad may be implemented such that the compressible feature has a nonuniform thickness.

The backup pad may be implemented such that the compressible feature has a conical cavity mounted on a conical surface of the backup pad.

The backup pad may be implemented such that the hardness of the compressible feature changes across the pad from its center toward its perimeter

The backup pad may be implemented such that the hardness of the compressible feature changes gradually across the pad.

The backup pad may be implemented such that the hardness of the compressible feature changes stepwise across the pad.

The backup pad may be implemented such that the compressible feature includes of concentric rings with different harnesses.

The backup pad may be implemented such that the hardness of the compressible feature decreases from the pad’s center toward its perimeter.

The backup pad may be implemented such that the change in the hardness of the compressible feature across the pad is proportional to distance from the center of the pad.

The backup pad may be implemented such that the backup pad has a nonplanar surface where a compressible feature with a uniform thickness is mounted on that surface.

The backup pad may be implemented such that the nonplanar surface of the backup pad is conical, hemispherical, or domed shape.

The backup pad may be implemented such that the backup pad causes the abrasive disc to have improved debris management compared to the abrasive disc on a backup pad with no compressible feature.

The backup pad may be implemented such that the backup pad causes the abrasive disc to have improved heat management compared to the abrasive disc on a backup pad with no compressible feature.

The backup pad may be implemented such that the backup pad in combination with the compressible feature causes the abrasive disc to have improved feature blending compared to the abrasive disc on a backup pad with no damping feature.

A spindle for a robotic abrasive system that includes a tool -engaging shaft. The spindle also includes a backup pad engaging surface. The backup pad engaging surface includes a pressure tuning feature that modifies a pressure profile exerted by the backup pad against a worksurface.

The spindle may be implemented such that the tool-engaging shaft engages a motive robotic arm.

The spindle may be implemented such that the motive robotic arm includes a force control unit.

The spindle may be implemented such that a controller adjusts the force control unit based on feedback received through the spindle.

The spindle may be implemented such that the pressure tuning feature includes a plurality of apertures in the backup pad engaging surface.

The spindle may be implemented such that the plurality of apertures extend completely through the backup pad engaging surface.

The spindle may be implemented such that the plurality of apertures couple to a debris removal tool.

The spindle may be implemented such that the plurality of apertures include a set of apertures arrange equidistant about the tool-engaging shaft.

The spindle may be implemented such that the set of apertures are substantially the same size.

The spindle may be implemented such that the set of apertures is a first set of apertures. The plurality of apertures includes a second set of apertures.

The spindle may be implemented such that the second set of apertures have a second radius larger than a first radius associated with the first set of apertures.

The spindle may be implemented such that the backup pad engaging surface is on a first side of a tool portion that is perpendicular to the tool-engaging shaft. The tool portion engages the tool-engaging shaft on a second side that is opposite the first side. A thickness separates the first and second sides.

The spindle may be implemented such that the first side has a first area, the second side has a second area. A second area is smaller than the first area such that an edge connecting the first and second area forms an angle with the backup pad engaging surface.

The spindle may be implemented such that the first area has a perimeter with a plurality of indentations. The spindle may be implemented such that the plurality of indentations are regularly spaced about the perimeter.

The spindle may be implemented such that the backup pad engaging surface has a perimeter with a plurality of indentations.

The spindle may be implemented such that the plurality of indentations are regularly spaced about the perimeter.

The spindle may be implemented such that the pressure tuning feature is elastically deformable.

The spindle may be implemented such that the pressure tuning feature is positioned between the backup pad and the abrasive disc.

EXAMPLES

These Examples are merely for illustrative purposes and are not meant to be overly limiting on the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

A combination of abrading experiments and Finite Element Analysis (FEA) modeling was used to compare performance attributes of abrasive backup pads described in the present disclosure to typical abrasive backup pads with uniform thickness flat foam layers. In each EXAMPLE the worksurface being abraded by an abrasive pad was planar and parallel to the surface of the abrasive disc used in the EXPERIMENT. Abaqus commercially available software (SIMULIA™ by Dassault Systemes®) was used to model abrasive backup pads against worksurfaces is some EXAMPLES where it was difficult or impossible to measure attributes of the backup pads experimentally.

EXAMPLE 1

In this EXAMPLE the abrading performance of an abrasive backup pad described in this disclosure like what illustrated in FIGS 2A-2C was evaluated using FEA modeling. FIG. 2E shows an axisymmetric cross section of the abrasive backup pad of this EXAMPLE worksurface. An axisymmetric FEA model with geometric parameters and material properties described in Table 1 below was developed in Abaqus. Backup pad 280 and a flat worksurface, laying down parallel to and contacting surface 284 of abrasive disc 286, are substantially harder than pressure tuning feature 290 in this EXAMPLE. Thus, rigid body constraints have been applied to backup pad 280 and the worksurface in the FEA model to reduce computational time. The worksurface was fixed in its location as a boundary condition and a vertical displacement loading, parallel to center line 292, was applied to backup pad in the FEA model.

Table 1. Geometric parameters and material properties of axisymmetric FEA model of

EXAMPLE 1

FIG. 11A shows the contact pressure profile between the abrasive pad and the worksurface under 0.03-inch impression of the pad against the worksurface predicted by the FEA model. The contact pressure decreases from the pad’s center to its edge. FIG. 11B displays stress contour plot of the deformed abrasive backup pad under 0.03-inch impression of the pad against the worksurface predicted by the FEA model. As indicated, the uniform compression of the pressure tuning feature applies a non-uniform stress across the pressure tuning feature, higher close to the center line of the pad and decreasing toward the edge of the pad, which causes a decreasing contact pressure between the abrasive disc and the worksurface from the pad’s center to its outer edge worksurface.

If this abrasive pad is rotating with an angular velocity of 60 RPM against the worksurface, with an assumed K_p = 1 one can determine the material removal rate from the worksurface across the pad’s surface using the empirical Preston equation [I. F. W. Preston, J. Soc. Glass. Technol., 11, 214, 1927] shown below. Fig. 11C shows the variation of the material removal (cut) rate across the pad’s surface. As indicated, the material removal rate of the abrasive disc of this EXAMPLE is almost uniform across the surface of the pad. Material removal rate = K_p x V x P Preston equation

K_p : material constant

V linear velocity

P: contact pressure

COMPARATIVE EXAMPLE 1:

In this EXAPLE the abrading performance of a typical abrasive backup pad with a uniform thickness foam layer mounted on a flat hard backup pad was evaluated using FEA modeling. FIG. 1 ID shows an axisymmetric FEA model of the abrasive backup pad of this EXAMPLE being used to abrade a flat worksurface, laying down parallel to and contacting the abrasive disc.

FIG. HE shows the contact pressure profile between the abrasive pad and the worksurface under 0.03-inch impression of the pad against the worksurface predicted by the FEA model. The contact pressure is uniform across the pad’s surface. FIG. 1 IF displays the stress contour plot of the deformed abrasive backup pad under 0.03-inch impression of the pad against the worksurface predicted by the FEA model. As indicated, the foam layer deforms uniformly across the pad causing a uniform contact pressure between the abrasive disc ant the worksurface across the pad.

With uniform contact pressure across the whole pad’s surface, and an increasing linear velocity from center to outer edge, the material removal rate then increases from center to the outer edge (as indicated schematically in FIG. 1C). If this abrasive pad is rotating with an angular velocity of 60 RPM against the worksurface, with an assumed K_p = 1 one can determine the material removal rate from the worksurface across the pad’s surface using the empirical Preston equation. FIG. 11G shows the variation of the material removal (cut) rate across the pad.

Comparing FIGS. 11C and 11G, one can conclude that the abrasive pad of FIG. 2E applies a much more uniform cut rate on the worksurface across the pad’s surface. Comparing the area under these curves, which shows the total cut from the worksurface, one can observe that the pad of FIG. 2E removes more material from the worksurface compared to the typical abrasive pad. EXAMPLE 2:

In this EXAMPLE the abrading performance of an abrasive backup pad like the pad illustrated in FIGS 2A-2C was evaluated. A 5 -inch diameter pad was made to test the concept of this pad in this disclosure experimentally. The pad had a metallic conical backup pad including a spindle fabricated out of 6061 Aluminum and a pressure tuning feature made of a multi-layered foam block with a conical cavity with the same profile as the conical backup pad. The foam block with cavity was made of 20 layers of 3M™ Cushion-Mount™ Plus Plate Mounting Tape E1060H which is a 0.06-inch thick double coated foam tape. The pad was made as follows:

• 20 circular disks with 5-inch outer diameter were cut out of the above Mounting Tape e using a laser cutting machine.

• Using the same laser cutting machine circular holes with appropriate diameters were cut out from 16 of 20 Mounting Tape disks so that by laminating these 16 ring layers a conical cavity with a profile similar to the conical backup pad was made.

• The 4 remaining intact Mounting Tape disks were laminated to each other and then the stack lamination was adhered to the bottom of the foam stack with cavity. At this point we had the pressure tuning feature with the central cavity.

• A layer of 3 mil thick double-sided Scotch VHB tape was adhered to the whole surface of the conical side of the metallic backup pad.

• The pressure tuning feature was mounted from its cavity side onto the VHB tape on the metallic conical backup pad.

• A 3M NX Disc Coated Aluminum Oxide Disc - Very Fine Grade - P180 Grit - 5 in Diameter - 31217 was adhered from its PSA side to the flat surface of the pressure tuning feature on the fabricated pad.

FIGS. 12A-12D illustrate the abrasive pad article made according to the process described above. FIG. 12A illustrates a metallic conical backup pad with spindle. FIG. 12B illustrates the pressure tuning feature made of multilayer foam block construction. FIG. 12C illustrates the abrasive pad assembly with an abrasive disc mounted on the free surface of the pressure tuning feature, and FIG. 12D illustrates a cutaway view taken along section line 12D- 12D illustrated in FIG. 12C.

Example 2 Abrasion Testing

The testing method consisted of loading the abrasive pad into a drill press. The drill press was obtained from McMaster-Carr, part number: 2799A21, which is an Economy Benchtop Drill Press with 120V AC, 13-1/4” maximum worksurface diameter. The drill press drives abrasive pad into a worksurface that is fixed on typical work bench table chuck. Material from the worksurface is removed during the drilling process. Specific steps of the test procedure are as follows:

1. Place a worksurface, which is a MIC 6 cast aluminum 6” x 6” flat sheet 0.5” in thickness (ground 6061 aluminum) on drill press table. Fastened down the worksurface to drill press table via 2 “C -clamps”

2. Set the drill press RPM (800 rpm) and duration of test (Imin).

3. Turn drill on and engage abrasive to the top surface of the worksurface under a fixed given load (5 lbs).

4. Remove and clean the worksurface . After removing the abraded worksurface from the drill table, the worksurface is clean with blown air out of a high-pressure nozzle (100 psi). A hand towel with water and IP A was used then to clean the worksurface of abraded surface dust.

5. Place the worksurface into a Nanovea HS2000 3D Non-Contact Profilometer and measure cut profile on its abraded worksurface.

FIG. 12E shows the cut profile of the worksurface abraded with the abrasive pad shown in FIGS. 12A-12D using the above test procedure. As indicated, a uniform cut was applied on the worksurface across the abrasive pad.

COMPARATIVE EXAMPLE 2:

In this EXAMPLE the abrading performance of a typical abrasive backup pad with a uniform thickness foam block mounted on a flat backup pad, currently being used in abrasive processes, was evaluated experimentally. A 5-inch diameter pad was fabricated using the same constitutive materials used in EXAMPLE 2. This pad has a metallic flat backup pad including a spindle fabricated out of 6061 Aluminum and a flat multi-layered foam block mounted on the flat surface of the metallic backup pad. The foam block was made of 7 layers of 3M™ Cushion-Mount™ Plus Plate Mounting Tape E1060H. The steps to make this pad is as follows:

• 7 circular disks with 5-inch outer diameter were cut out of the above Mounting Tape using a laser cutting machine. • All the circular disks made in the previous step were laminated to each to make a cylindrical foam block.

• A layer of 3 mil thick double-sided Scotch VHB tape was adhered to the whole flat surface of the metallic backup pad.

• The foam block was mounted on of its surface onto the VHB tape on the flat backup pad.

• A 3M NX Disc Coated Aluminum Oxide Disc - Very Fine Grade - P180 Grit - 5 in Diameter - 31217 was adhered from its PSA side to the flat surface of the multi-layered foam block of the fabricated pad apart from the metallic backup pad.

The resulting construction is illustrated in FIGS. 12F-12I. The flat backup pad is illustrated in FIG. 12F, the multilayer foam block in FIG. 12G, and the entire assembly in FIG. 12H. FIG. 121 illustrates a cutaway view of the assembly of 12H along a section lines 121- 121. The same abrasion test procedure as the one described in Example 2 Abrasion Testing above was used to evaluate the abrading performance of the abrasive pad of this EXAMPLE.

The resulting cut profile of the abrasive pad 12F is illustrated in FIG. 12J. As illustrated, a nonuniform cut, increasing from the pad center to its edge, was applied on the worksurface across the abrasive pad.

EXAMPLE 3

In this EXAPLE the abrading performance of an abrasive backup pad with concentric rings pressure tuning feature like what illustrated in FIGS 3A and 3B in this disclosure was evaluated experimentally. A 5-inch diameter pad was made to test the concept of this pad in this disclosure. The pad had a metallic flat backup pad including a spindle fabricated out of 6061 Aluminum, such as what illustrated in FIG 12F, and a pressure tuning feature made of 3 rings, such as what illustrated in FIG 3A. The pad was made as follows:

• 2 circular disks with 1 ,666-inch outer diameter were cut out of Resilient Polyurethane Foam Sheet - Soft (0.25 -inch thick, Pressure to Compress 25% of 11 psi) obtained from McMaster-Carr, part number: 86375K134 using a laser cutting machine.

• The 2 circular disks made in the previous step were laminated to each other using a layer of 3 mil thick double-sided Scotch VHB tape. This laminate would be used as the central part of the pressure tuning feature in the pad.

• Using the same laser cutting machine a circular ring with a 1 ,666-inch inner diameter and a 3.333-inch outer diameter was cut out of Resilient Polyurethane Foam Sheet - Ultra Soft (0.5-inch thick, Pressure to Compress 25% of 3psi) obtained from McMaster-Carr, part number: 86375K114 using a laser cutting machine. This ring would be used as the intermediate concentric ring of the pressure tuning feature in the pad.

• Using the same laser cutting machine another circular ring with a 3.333-inch inner diameter and a 5 -inch outer diameter was cut out of Super-Cushioning Polyurethane Foam Circle (0.5-inch thick, Pressure to Compress 25% of 0.3psi) obtained from McMaster-Carr, part number: 8883K54 using a laser cutting machine. This ring would be used as the outer concentric ring of the pressure tuning feature in the pad.

• The circular laminate and the two concentric rings made in the previous steps were mounted on of their surfaces onto the VHB tape on the flat backup pad.

• A 3M NX Disc Coated Aluminum Oxide Disc - Very Fine Grade - P180 Grit - 5 in Diameter - 31217 was adhered from its PSA side to the flat surface of the concentric rings pressure tuning feature the fabricated pad apart from the metallic backup pad.

The same abrasion test procedure as the one described in Example 2 Abrasion Testing above was used to evaluate the abrading performance of the abrasive pad of this EXAMPEE, The resulting cut profile of the abrasive pad of this EXAMPLE is illustrated in FIG. 13A. As illustrated, a nonuniform cut pattern was applied on the worksurface across the abrasive pad. The central portion of the abrasive pad removed the most material and the outer portion of the abrasive pad removed the least material from the worksurface while as illustrated in FIG. 12J, using a typical abrasive pad with a flat foam layer the cut rate increases from the pad’s center toward its edge due to linear velocity increase toward the pad’s edge.

A FEA model of the abrasive pad of this EXAMPLE against a flat worksurface laying down parallel to the surface of abrasive disc was then developed. The same geometries were used for the metallic backup pad, the central foam disc and the concentric rings of the pressure tuning feature. Elastic moduli of 11, 3 and 0.3 psi as well as Poisson’s ratios of 0.4, 0.1 and 0.1 were used as material properties of the central disc, intermediate and other concentric rings respectively in the FEA model. Rigid body constraints were applied to the metallic backup pad and the worksurface to reduce computational time as they were substantially harder than the pressure tuning feature. A compressive load of 5 Ibf was applied to the spindle of the backup pad against the worksurface while the worksurface was fixed in place. FIG. 13B shows the FEA predicted contact pressure profile between the abrasive pad and the worksurface. As illustrated the contact pressure was substantially larger in the central region of the disc above the central disc of the pressure tuning feature and it decreased toward the edge of the abrasive disc. The reason behind this contact pressure profile lies in the distribution of the hardness of materials used in the pressure tuning feature which causes a significantly higher compressive stress in the central region of the disc than the regions above the concentric rings as illustrated in FIG. 13C.

The materials used to make the pad of this EXAMPLES had been selected arbitrary to just show the effect of hardness variation of the pressure tuning feature across the pad on the cut rate performance of the pad. However, by adjusting the number of concentric rings and their hardness across the pad, one can tune the cut pattern and obtain a desired cut profile across the pad.

EXAMPLE 4

In this EXAMPLE the abrading performance of an abrasive backup pad with a nonuniform surface like what illustrated in FIGS. 14A-14C in this disclosure was evaluated experimentally. A 5-inch diameter pad was made to test the concept of this pad in this disclosure. The pad had a metallic backup pad including a conical surface on one side and a flat surface with a spindle on the other side which was fabricated out of 6061 Aluminum, such as the backup pad illustrated in FIG. 14A, and a pressure tuning feature made of a foam layer with a uniform thickness of 0.5-inch. The pad was made as follows:

• A circular disk with 5-inch outer diameter were cut out of Resilient Polyurethane Foam Sheet - Ultra Soft (0.5-inch thick, Pressure to Compress 25% of 3psi) obtained from McMaster-Carr, part number: 86375K114 using a laser cutting machine.

• A layer of 3 mil thick double-sided Scotch VHB tape was adhered to the whole conical surface of the metallic backup pad.

• The circular foam disc made in the previous steps was mounted on of its surfaces onto the VHB tape on the conical backup pad.

• A 3M NX Disc Coated Aluminum Oxide Disc - Very Fine Grade - P180 Grit - 5 in Diameter - 31217 was adhered from its PSA side to the free surface of the pressure tuning feature of the fabricated pad apart from the metallic backup pad.

The same abrasion test procedure as the one described in Example 2 Abrasion Testing above was used to evaluate the abrading performance of the abrasive pad of this EXAMPLE. The resulting cut profile of the abrasive pad of this EXAMPLE is illustrated in FIG. 14D. As illustrated, a uniform cut pattern was applied on the worksurface across the abrasive pad. By engaging the abrasive pad against the worksurface the central region of the abrasive pad which was closer to the worksurface contacted the worksurface first and the central region of the pressure tuning feature was compressed to let the other areas on the abrasive disc come in to contact with the worksurface. Therefore, the central area of the abrasive disc was in contact the worksurface for a longer time during the abrasive presses which led to a higher material removal from the areas close to the center of the pad. Also, the central region of the pad went under more compression which made this area harder than other areas of the pad due to densification of the foam layer. This caused higher contact pressure under the central area of the pad and a decreasing contact pressure profile toward the edge of the pad which in turn compensated the increasing linear velocity of the pad toward its edge. Consequently, the pad made a uniform material removal from the worksurface across the pad.

Claims

36 CLAIMS What is claimed is:

1. A method of managing the contact pressure across an abrasive disc, the method comprising: coupling the abrasive disc to a backup pad comprising a pressure tuning feature that causes an experienced pressure by a worksurface, across a radius of the abrasive disc, to be uniform; abrading a worksurface by contacting the abrasive disc to the worksurface; and wherein the backup pad causes the abrasive disc to have a cut rate that is substantially uniform across the surface of the abrasive disc when compared to the abrasive disc on a backup pad with no pressure tuning feature.

2. The method of claim 1, wherein the pressure tuning feature is elastically deformable.

3. The method of claim 1, wherein the pressure tuning feature is positioned between the backup pad and the abrasive disc.

4. The method of claim 1, wherein the pressure tuning feature comprises a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric layer, a nonwoven layer, or a soft rubber.

5. The method of claim 1 , wherein the pressure tuning feature is made of multiple layers or multiple materials in a layered or agglomerate construction.

6. The method of claim 1, wherein the backup pad includes channels extended from the surface of the pressure tuning feature, where the abrasive disc is mounted, to the opposite side of the backup pad for dust and debris extraction.

7. The method of claim 1, wherein the pressure tuning feature has a nonuniform thickness.

8. The method of claim 1, wherein the pressure tuning feature has a conical cavity mounted on a conical surface of the backup pad.

9. The method of claim 1, wherein the hardness of the pressure tuning feature changes across the pad from its center toward its perimeter.

10. A backup pad for an abrasive system, the backup pad comprising: a tool engaging feature; an abrasive article engaging feature; and 37 a compressible feature that changes a cut rate profile of an abrasive article attached to the abrasive article engaging feature.

11. The backup pad of claim 10, wherein the tool engaging feature is on a first side of the backup pad and the abrasive article engaging feature is on a second side of the backup pad, wherein the first side opposes the second side.

12. The backup pad of claim 10, wherein the compressible feature is elastically deformable.

13. The backup pad of claim 10, wherein the compressible feature is positioned between the backup pad and the abrasive disc.

14. The backup pad of claim 10, wherein the compressible feature comprises a material which has been patterned, 3D printed, embossed, or engraved to provide the desired deformability.

15. The backup pad of claim 10, wherein the compressible feature comprises a foam, an engraved, structured, 3D printed, or embossed elastomer, a fabric or nonwoven layer, or a soft rubber.

16. The backup pad of claim 10, wherein the compressible feature is made of multiple layers and / or multiple materials in a layered or agglomerate construction.

17. The backup pad of claim 10, wherein the backup pad includes channels extended from a surface of the damping feature to the opposite side of the backup pad.

18. The backup pad of claim 10, wherein the compressible feature includes a material having an elastic modulus of less than about 650 psi.

19. The backup pad of claim 10, wherein the compressible feature has a nonuniform thickness.

20. The backup pad of claim 10, wherein the compressible feature has a conical cavity mounted on a conical surface of the backup pad.

21. The backup pad of claim 10, wherein the hardness of the compressible feature changes across the pad from its center toward its perimeter.

22. The backup pad of claim 21, wherein the hardness of the compressible feature changes gradually across the pad.

23. The backup pad of claim 21, wherein the hardness of the compressible feature changes stepwise across the pad.

24. The backup pad of claim 21, wherein the compressible feature comprises of concentric rings with different harnesses.

25. The backup pad of claim 21, wherein the hardness of the compressible feature decreases from the pad’s center toward its perimeter.

26. The backup pad of claim 21, wherein the change in the hardness of the compressible feature across the pad is proportional to distance from the center of the pad.

27. The backup pad of claim 21, wherein the backup pad has a surface that is conical, hemispherical, or domed shape.

28. A spindle for a robotic abrasive system, the spindle comprising: a tool-engaging shaft; a backup pad engaging surface; and wherein the backup pad engaging surface comprises a pressure tuning feature that modifies a pressure profile exerted by the backup pad against a worksurface.

29. The spindle of claim 28, and wherein the tool-engaging shaft engages a motive robotic arm.

30. The spindle of claim 29, and wherein the motive robotic arm comprises a force control unit.

31. The spindle of claim 30, and wherein a controller adjusts the force control unit based on feedback received through the spindle.

32. The spindle of claim 28, wherein the pressure tuning feature comprises a plurality of apertures in the backup pad engaging surface.

33. The spindle of claim 32, wherein the plurality of apertures extend completely through the backup pad engaging surface.

34. The spindle of claim 32, wherein the plurality of apertures couple to a debris removal tool.

35. The spindle of claim 32, wherein the plurality of apertures comprise a set of apertures arrange equidistant about the tool-engaging shaft.

36. The spindle of claim 32, wherein the set of apertures are substantially the same size.

37. The spindle of claim 32, wherein the set of apertures is a first set of apertures, and wherein the plurality of apertures comprises a second set of apertures. The spindle of claim 37, wherein the backup pad engaging surface is on a first side of a tool portion that is perpendicular to the tool-engaging shaft, and wherein the tool portion engages the tool-engaging shaft on a second side that is opposite the first side, and wherein a thickness separates the first and second sides, wherein the first side has a first area, the second side has a second area, and wherein second area is smaller than the first area such that an edge connecting the first and second area forms an angle with the backup pad engaging surface. The spindle of claim 29, wherein the backup pad engaging surface has a perimeter with a plurality of indentations . The spindle of claim 39, wherein the pressure tuning feature is positioned between the backup pad and the abrasive disc.