Patent Application
20070298687
Referring to
Generally disc-holding unit 200 includes disc chuck 210 having disc-mounting surface 215. In a typical operation, a disc is releasably held against the disc-mounting surface. In some embodiments, the disc chuck is a vacuum chuck. Generally, a vacuum chuck includes a vacuum source to create a vacuum at the disc-mounting surface sufficient to hold the disc in place during the edge modifying operation. In some embodiments, adhesives, e.g., pressure sensitive adhesives and non-pressure sensitive adhesives, may be used to hold the disc against the disc-mounting surface. Other known means of holding the disc against the disc-mounting surface, e.g., mechanical devices, may also be used.
In some embodiments, disc-holding unit 200 includes positioning assembly 220. The positioning assembly is used to bring edge 255 of disc 250 in contact with, e.g., abrasive article 320. In some embodiments, the positioning assembly can be used to apply a contact force, e.g., a fixed contact force, between the edge of the disc and the surface of the abrasive article. In some embodiments, the positioning assembly can be used to retract the disc from the abrasive article during and/or following the edge modifying operation.
In some embodiments, the positioning assembly comprises a piston connected to a pneumatic or hydraulic source. In some embodiments, the positioning assembly comprises a motor mechanically coupled to the disc holding unit. Other mechanisms for the controlled positioning of one element relative to another are well known in the art.
Disc-holding unit 200 also includes drive shaft 225 mechanically coupled to motor 230. Motor 230 rotates drive shaft 225, and ultimately disc chuck 210 and disc 250 about disc chuck axis of rotation 205, as shown by arrow A. Generally, the disc may be rotated counterclockwise or clockwise about the disc chuck axis of rotation.
In some embodiments, edge-modifying unit 300 includes abrasive article support 310 mechanically coupled to drive shaft 315, which is mechanically coupled to motor 330. Motor 330 rotates drive shaft 315 and ultimately abrasive article support 310 about support axis of rotation 305, as shown by arrow B. Generally, the abrasive article support may be rotated counterclockwise or clockwise about the support axis of rotation.
In some embodiments, the abrasive article support and the disc are co-rotating, i.e., both are rotated clockwise or counterclockwise about their respective axis of rotation. In some embodiments, the abrasive article support and the disc are counter-rotating.
In some embodiments, disc chuck axis of rotation 205 and support axis of rotation 305 are co-planar. In some embodiments, disc chuck axis of rotation 205 and support axis of rotation 305 are parallel. As shown in
In some embodiments, the disc chuck axis of rotation and the support axis of rotation are not co-planar. For example, in some embodiments, the disc chuck axis of rotation also is tilted with respect to the plane initially formed by the disc chuck axis of rotation and the support axis of rotation by a further rotation about an axis, perpendicular to the disc chuck axis of rotation, which passes through the centroid of the area of contact between the disc and the abrasive article. Generally, the angle of tilt may range from about 15 degrees to about 50 degrees. In some embodiments, the tilt angle is at least about 30 degrees, and in some embodiments at least about 40 degrees.
In some embodiments, abrasive article 320 circumferentially wraps cylindrical surface 311 of abrasive article support 310. In some embodiments, the fixed abrasive article is attached to abrasive article support 310, e.g., mechanically or adhesively attached. In some embodiments, the abrasive article is a belt that only partially wraps the cylindrical surface of the support. The web path of such a belt may pass over one or more additional driven and/or idler rollers. In some embodiments, abrasive article support 310 is an idler roller. In such embodiments, the abrasive belt will cause the support to rotate as it passes over at least a portion of the cylindrical surface of the support. In some embodiments, abrasive article support 310 is a driven roller. In some embodiments, the abrasive article support will be stationary, e.g., a shoe. In some embodiments, the stationary support may include a mean to reduce friction between the abrasive article and the surface of the support as the abrasive article is passes over the support. Exemplary means to reduce friction include a fluid bearing, e.g., an air bearing.
Generally, any known abrasive article may be used. In some embodiments, the abrasive article is a fixed abrasive article. In some embodiments, the abrasive article may be a three-dimensional fixed abrasive article having abrasive particles dispersed throughout at least a portion of its thickness such that erosion exposes additional abrasive particles. The abrasive article can also be textured such that it includes raised portions and recessed portions in which at least the raised portions include abrasive particles in a binder. Exemplary fixed abrasive articles are described, e.g., in U.S. Pat. Nos. 5,014,468; 5,453,312; 5,454,844; 5,692,950; 5,820,450; and 5,958,794; and in WO 98/49723.
In some embodiments, the fixed abrasive article may include a backing. Any known backing may be used. For example, polymeric films, fabrics, metal foils, nonwovens, and combinations thereof may be used. In addition, Bruxvoort et al. in U.S. Pat. No. 5,958,764 (column 17, line 12 through column 18, line 15 of which is incorporated herein by reference) describe useful backings. Particular selection is within the skill in the art.
In some embodiments, fixed abrasive articles include abrasive composites. Abrasive composites are known in the art of fixed abrasive articles and may comprise abrasive particles dispersed throughout a binder. In some embodiments, an abrasive composite may comprise a polymeric material having separate phases, with one phase acting as abrasive particles.
Generally, any known binder may be used. For example, (meth)acrylates, epoxies, urethanes, polystyrenes, vinyls, and combinations thereof may be used. In addition, Bruxvoort et al. in U.S. Pat. No. 5,958,764 (column 22, line 64 through column 34, line 5 of which is incorporated herein by reference) describe useful binders. Particular selection is within the skill in the art.
Generally, any known abrasive particles may be used including, e.g., diamonds, silicon carbide, and/or boron nitride particles. In addition, Bruxvoort et al. in U.S. Pat. No. 5,958,764 (column 18, line 16 through column 21, line 25 of which is incorporated herein by reference) describe useful abrasive particles. In some embodiments, the abrasive particles may be in the form of abrasive agglomerates, which comprise a plurality of individual abrasive particles bonded together to form a unitary particulate mass. Examples of abrasive agglomerates are further described in U.S. Pat. Nos. 4,652,275; 4,799,939; and 5,500,273.
In some embodiments, the abrasive article comprises a compressible composite layer. In some embodiments, the composite layer includes a binder and abrasive agglomerates. In some embodiments, the composite layer comprises at least 50% by volume of the binder. In some embodiments, the binder comprises a material selected from the group consisting of urethanes, epoxies, and combinations thereof. In some embodiments, the composite layer further comprises inorganic fillers.
Exemplary abrasive agglomerates useful in a compressible composite layer include those described above. In some embodiments, the abrasive agglomerates comprise abrasive particles dispersed in an inorganic matrix. In some embodiments, the inorganic matrix is selected from the group consisting of a glass, a ceramic, and a glass ceramic. In some embodiments, the abrasive particles are diamonds, silicon carbide, and/or boron nitride particles.
In some embodiments, the abrasive articles include a support to which the compressible composite layer is bonded. In some embodiments, the compressible composite layer is directly bonded to the support. In some embodiments, one or more bonding layers are interposed between the compressible composite layer and the support.
Various embodiments of the edge modifying apparatus of present disclosure provide a relative motion between the edge of the disc being modified and the modifying surface, e.g., the abrasive surface of a fixed abrasive article via the co-rotation or counter rotation of the disc and the fixed abrasive article support. In some embodiments, it may be desirable to provide additional relative motion between the edge of the disc being modified and the modifying surface, e.g., the abrasive surface of a fixed abrasive article. For example, in some embodiments, it may be desirable to linearly oscillate the disc and the fixed abrasive article relative to one another.
In some embodiments, this linear oscillation may provide additional disc edge modification due to the motion of the edge of the disc relative to the abrasive surface of the fixed abrasive article. In some embodiments, the linear oscillation may enable a greater area of the fixed abrasive article to contribute to the edge modifying process.
In some embodiments, the linear oscillation may reduce or eliminate grooving of the fixed abrasive article. “Grooving” arises when the edge of a disc is pressed against the abrasive surface of fixed abrasive article and a relative rotational motion is created between the edge of the disc and the abrasive surface. As the edge of the disc is modified, the abrasive article may develop a wear pattern corresponding to the area of contact between the edge of the disc and the fixed abrasive article. If the edge of the disc is fixed relative to the surface of the fixed abrasive article, this can lead to a groove in the surface of the fixed abrasive article. Such a groove may detrimentally affect the edge polishing operation and can require premature replacement of the abrasive article.
Generally, linear oscillation of the edge of a disc relative to the surface of the abrasive article effectively expands the area of contact between the edge of the disc and the abrasive article. In some embodiments, this leads to the more uniform wearing of the surface of the abrasive article, which may reduce or eliminate grooving.
In some embodiments, the disc may be oscillated relative to an abrasive article held in a fixed position. In some embodiments, the abrasive article may be oscillated relative to a disc held in a fixed position. In some embodiments, both the abrasive article and the disc may be oscillated relative to each other.
One means to linearly oscillate the edge of a disc relative to the surface of the abrasive article is shown in
In some embodiments, it may be desirable to have a substantially constant linear oscillation velocity across the face of the abrasive article during each half-cycle of oscillation. Generally, a substantially constant linear oscillation velocity will result in more evenly worn abrasive article, and may create a more uniform polish of the workpiece.
In some embodiments, it may be desirable to oscillate the disc relative to the abrasive article and/or the abrasive article relative to the disc using a uniform velocity oscillation driver coupled to at least one of the disc chuck and the abrasive article support. As used herein, “a uniform velocity linear oscillation driver” provides a substantially constant oscillation velocity during at least 80% of each half-cycle of oscillation. As used herein, the linear oscillation velocity is “substantially constant” if it varies less than ±5% from the average linear oscillation velocity over the period of interest. In some embodiments, the linear oscillation velocity varies by less than ±3%, or even by less than ±1% from the average linear oscillation velocity over the period of interest
In some embodiments, the uniform velocity oscillation driver may comprise one or more of a stepper motor, a screw drive, a magnetic drive, a linear gear, and the like. Generally, selection of the means used to oscillate is within the ability of one of ordinary skill in the art.
In some embodiments, the uniform oscillation driver comprises a reversible motor. The motor may be either a direct current (DC) or alternating current (AC) motor. In some embodiments, the motor is a stepping motor. In some embodiments, the uniform oscillation driver comprises controls to reverse the direction of the reversible motor. For example, in some embodiments, the controls may comprise limit switches. In some embodiments, the controls may comprise a programmed stepping motor controller. In some embodiments, the uniform velocity oscillation driver comprises an eccentric driven by a stepping motor. In some embodiments, the stepper motor is driven with a pulse chain that compensates for the non-linear movement of the eccentric such that the oscillation speed is linear between the reversals.
In some embodiments, the uniform velocity oscillation driver may comprise a cam coupled to a cam follower. A cam can be created to deliver a substantially constant linear oscillation velocity across the abrasive article. To design such a cam one would start with the traverse distance and the minimum radius of the cam compatible with the mechanical components of the cam drive and the cam follower. For example if a cam is to have a 2 unit throw (wherein a “unit” is an arbitrary measure of distance), a single lobe (one traverse per cam rotation), and a minimum radius of 1 unit; then the radius needs to increase linearly as a function of angle from 1 unit to 3 units for 180 degrees of the cam and then decrease linearly back to 1 unit over the angle 180 degrees to 360 degrees. Table 1 shows the desired cam radius as a function of the angle for such a cam.
As shown in Table 1, the polar coordinates can be converted to Cartesian coordinates. A cam can then be made by entering the numbers from such a table into the spline function of a drawing program, printing out a full size drawing, adhering the drawing to a cam substrate (e.g., a piece of sheet metal), and cutting out the cam with, e.g., a band saw, by following the line of the drawing. Other means of creating cam of a desired shape are known in the relevant art.
The movement of a cam follower tracking the peripheral edge of the cam described by Table 1 is shown in
Because the displacement is linear, the rate of change in displacement per unit time is substantially constant during each half-cycle of rotation. As a practical matter, it may be difficult or undesirable to make the sharp transition in velocity between half-cycles of oscillation (see, e.g.,
For example, a cam was created to deliver a substantially constant oscillation velocity across the abrasive article. To design such a cam one would start with the traverse distance and the minimum radius of the cam compatible with the mechanical components of the cam drive and the cam follower. The desired radius of a function of angle is then generated, and the polar coordinates are converted to x-y coordinates, as shown in Table 2 for a cam having a minimum radius of 6.4 millimeters (mm) (0.25 inches), and a maximum radius of 57.2 mm (2.25 inches).
Using the x-y coordinates provided in Table 2, AutoCad LT generated the shape of a cam using a spline function. The spline fit automatically rounded the cam shape at 0 and 180 degrees. A cam was made by the manner described above and had the heart shape shown in
Peripheral edge 620 includes rounded portions 621 and 622 at the locations of minimum distance and maximum distance, respectively. Depending, e.g., on the degree of rounding of the peripheral edge of the cam at the transition regions between the first and second half-cycles of oscillation, the linear oscillation velocity will not be constant in these transition regions. In some embodiments, the peripheral edge is defined by a curve resulting in a substantially constant linear oscillation velocity during at least 80% of each half-cycle of oscillation between the transition regions. In some embodiments, the peripheral edge is defined by a curve resulting in a substantially constant linear oscillation velocity during at least 90% of each half-cycle of oscillation. In some embodiments, the peripheral edge is defined by a curve resulting in a substantially constant linear oscillation velocity during at least 95%, or even at least 98%, of each half-cycle of oscillation.
Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention.
