Tool, apparatus, and method for precision polishing of lenses and lens molds
A tool for polishing objects having a wide variety of materials and shapes including precision optical surfaces, injection mold inserts, and thin film coating dies. The tool has an elastic solid bladder with a curved surface, upon which is disposed an abrasive band. The curved bladder surface is produced by compressing the bladder between two parallel plates. The apparatus comprises a multi-axis computer controlled machine to which the tool is attached.
This application is a continuation-in-part of copending patent application U.S. Ser. No. 10/863,702, filed on Jun. 8, 2004, which is a continuation-in-part of copending patent application U.S. Ser. No. 10/439,833, filed on May 16, 2003, the disclosures of which are incorporated herein by reference.
FIELD OF THE INVENTIONA polishing tool for correcting surface errors, and for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts.
BACKGROUND OF THE INVENTIONThis invention relates to tools, an apparatus, and a method for correcting figure errors, and for polishing a wide variety of materials and shapes including but not limited to precision optical surfaces, injection mold inserts, thin film coating dies, and the like. The method of the present invention provides for improving and further finishing of any surface, ranging from a relatively rough ground surface to a polished surface.
Typically the part being finished according to the present invention is measured with a coordinate measurement machine (CMM), a surface profilometer, an interferometer, microscope or some other measuring instrument capable of giving surface roughness and or profile data. The data from such measurement and analysis is then entered into a machine process-controlling computer that then manipulates the data into process parameters for improving or polishing the desired component by a polishing machine of the present invention. One or more iterations of the process of the present invention may be required to achieve the desired results. In the preferred embodiment, a polishing tool comprising an inflatable bladder is attached to and driven by the tool spindle of the polishing machine. The part to be improved or polished, whether spherical, aspherical or parabolic in shape, is placed into the work piece spindle of the polishing machine. If such part is not axially symmetrical, it may be held in a braked position in the work piece spindle, or held in a fixture on a table of the machine. The polishing tool is then compressed against and traversed in a path over the component. Several variables are able to be controlled as process parameters, so that the desired finishing results are achieved.
In another preferred embodiment, the polishing tool further comprises actuation means to extend and/or position and/or compress the inflatable bladder or other compliant part with respect to the part to be improved or polished. Such actuation means may comprise one or more linear actuating devices such as e.g., air operated or hydraulically operated cylinders.
The present invention provides a method and apparatus for which the main goal is to polish out and remove defects left from a preceding grinding operation or to improve the accuracy of a workpiece such as a lens, mirror, insert for an injection mold, or coating die, such accuracy being relative to the intended use of the workpiece; and also to improve the economy of the polishing process.
In the following specification, for the sake of linguistic simplification, only optical components, also known as precision optics or optics generally, are typically mentioned as the workpiece. However, it is to be understood that all lenses, spherical and aspherical, conformal optics, mirrors, plano shapes, injection mold components, coating dies, and other articles of manufacture that require highly polished accurate surfaces are also included in the description, and are to be considered as being within the scope of the present invention. Materials that may be finished using the method and apparatus of the present invention include, but are not limited to brittle amorphous materials such as e.g., glass, ceramics, infrared materials such as quartz, and the like. Also included are metals such as e.g., tool steel, stainless steel, and the like; crystalline materials such as e.g. silicon; and any other workpieces requiring high finish and form specifications.
Currently, many optical lenses are made beginning with a “blank” starting part (such blank part being an approximately formed and generally roughly finished piece) in several processing steps. The process steps typically include fine grinding, followed by conventional polishing techniques wherein the surface roughness and surface accuracy of the lens is significantly improved. This prior art process is sufficient for many conventional low-precision lenses, but when the desired lens has a shape that is not spherical or plano and/or where such conventional methodologies cannot be applied e.g., aspherics, or where the lens has very high accuracy requirements, such prior art process is not sufficient. In such circumstances, the method and apparatus of the present invention is advantageous.
In particular, several prior art procedures are known to the applicants as being used to fabricate precision optics. One of these procedures is known in the art as small spot tool polishing, wherein a pencil like polishing tool (typical 5 to 15 millimeters in diameter) is used, such tool comprising a polishing medium of polyurethane, felt, pitch or some other combination of polishing material bonded thereto, and typically known as a foil.
In one specific embodiment of the small spot tool polishing process, a polishing tool, rotating around the axis thereof, is mounted to a robotic arm and is traversed by such arm across the lens surface, or alternatively, such tool is built into a computer numerically controlled (CNC) polishing machine. During the process a polishing suspension is applied, while the polishing tool is traversed across the lens surface through a predetermined typically computer controlled path. Depending on the correction geometry required, different volumes of material are abraded, or polished, from the lens surface. The robotic arm of the correction machine is programmed in such a way that the polishing tool is moved with different dwell times at different positions as such tool passes over the lens. Thus, when more material must be removed at a particular location, the dwell time is increased, and vice versa. During the polishing process, the lens may be rotate around its axis, or be it may be fixed in specific positions if the robotic arm of the correction machine has such capability.
In the small spot procedure there are several disadvantages. The polishing tool wears quickly due to its small diameter, which results in the distinct disadvantages of a) typically very long polishing cycles; and b) because of quicker degradation of the small polishing foil it is much more difficult and costly to develop accurate corrective polishing routines. Another disadvantage is due to the small spot diameter of the tool. Material removal rates are typically very slow, since the performance is directly proportional to the size of the surfaces that are in contact during the polishing routine.
Another known finishing/polishing procedure is known as magnetorheological finishing (MRF). With the use of the MRF process, marked improvements in surface roughness and accuracy can be achieved. In general, the MRF process produces better results than small spot polishing. Reference may be had e.g., to U.S. Pat. Nos. 5,795,212, 6,106,380 (deterministic magnetorheological finishing), 5,839,944 (apparatus deterministic magneto-rheological finishing), 5,971,835 (system for abrasive jet shaping and polishing of a surface using a magnetorheological fluid), 5,951,369, 6,506,102 (system for magnetorheological finishing of substrates), and 6,267,651 and 6,309,285 (magnetic wiper). The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification.
With the MRF procedure a polishing suspension is used, which contains particles that can be magnetized and therefore under the effect of strong electromagnets can be solidified. A polishing suspension is applied sequentially on the outside surface of a cylinder rotating around its horizontal axis. The polishing suspension is disposed in a thin band upon the outside surface of a rotating cylinder, and is conveyed to a location where a strong magnetic field is focused. This field is created by magnets surrounding both sides of the wheel. Under the influence of the magnetic field, the polishing suspension increases in viscosity until it is substantially an abrasive solid, thereby forming a stiff polishing body, which becomes the polishing tool. Thus within this area i.e., in the upper apex of the polishing tool, a lens may be polished by such solidified MRF fluid. As the wheel rotates the polishing suspension leaves the contact area of the lens and the magnetic field, and is then vacuumed/wiped off of the wheel and continuously recirculated.
During the MRF polishing process, the lens rotates. The lens carrier with the lens can be placed by means of a tilting device and an assigned axis control at angles to the vertical axis. With a large angle of inclination, the edge of the lens touches the polishing tool, while with a small angle of inclination the center of the lens comes into contact with the polishing tool. Additionally the lens carrier is guided in such a way that it also can execute vertical movements. With a rotating lens, the angles of inclination are continually varied; such variation is accomplished with the use of virtual pivot point computer controlled motion that combines the two linear and one rotary axes and thus keeps the lens in consistent contact with the polishing tool. A spiral develops on the lens that is the trajectory of the point of contact between the solidified polishing suspension and the lens surface.
The different material removals necessary for the correction of the lens geometry are implemented as follows: The dwell time of the point of contact on a certain area on the lens surface can be varied by appropriately controlling the courses of motion. Since the material removal is proportional to the dwell time, the desired corrections can be achieved. The polishing suspension in its “firmness” can be influenced by variation of the magnetic field strength. This further enables different material removal rates. A further correction option results by varying the depth of submergence of the lens into the polishing suspension.
Although the MRF process has many attributes, such process also has some distinct disadvantages as follows: 1) Cost-effective polishing of deviations is limited to errors of less than 200 nanometers only. This is a result of the lack of “stiffness” of the magnetically stiffened polishing suspension and the ability to shear/polish features greater in magnitude. 2) There is a very high capital cost of entry into the MRF technology. The process entails very complex technology, which also increases the cost of operation. It is also necessary to continuously change the MRF polishing suspension, which is very expensive because of its proprietary nature. 3) Parts made of magnetic materials are not able to be polished with this process, as the workpiece will become magnetized and not release the magnetic process fluid. 4) Small concave parts cannot be polished due to the configuration and size of the MRF polishing wheel.
Reference may be had to German patent DE003 1057 of R. Mandler, the disclosure of which is incorporated herein by reference. There is disclosed in such patent a method for polishing of lenses and mirrors for high resolution optics. The lens/mirror is polished conventionally and measured by interferometric means to map the surface and to determine how much material needs to be removed and from where. The lens is supported on a rotating holder with two degrees of movement, while the polishing wheel is supported with axial adjustment. The polishing wheel has a flexible rim inflated with a variable internal pressure to adjust the hardness of flexible rim/tire. Mandler relies upon changes in pressure on a polyurethane foil to impact removal rates and finishing qualities. Although as stated therein, the apparatus of Mandler can change the pressure during the process, such process does not have the ability to change to softer media, such as felt or other softer synthetic materials as is disclosed and claimed in this application. Mandler also discloses only a 3-axis process, whereas embodiments of the present invention include control and operation with respect to five or more axes.
With the method and apparatus of the present invention, many of the disadvantages of the aforementioned techniques are non-existent, or rendered insignificant. It is therefore an object of this invention to provide an apparatus for precision polishing of objects comprising a wide variety of materials and shapes.
It is a further object of this invention to provide a versatile and adjustable tool for precision polishing of objects comprising a wide variety of materials and shapes.
It is another object of this invention to provide a method for precision polishing of objects comprising a wide variety of materials and shapes.
It is an object of this invention to provide a method and apparatus for precision polishing of objects that is simple and has a low operating cost.
It is an object of this invention to provide a method, a tool, and an apparatus that in having the ability to remove low, mid, and high spatial surface errors, reduces the requirements of the pre-fine grind tolerances, which in turn reduces the requirements of the fine grinding apparatus.
It is an object of this invention to provide a method and apparatus for precision polishing of objects that has a high rate of material removal.
It is an object of this invention to provide a tool for precision polishing of objects that has high longevity and stability of operation.
It is an object of this invention to provide a method, a tool, and an apparatus that has the ability to perform polishing of object surfaces that are deeply concave in shape.
SUMMARY OF THE INVENTIONIn accordance with the present invention, there is provided a polishing tool comprising a mandrel having a drive shank at a proximal end thereof, a threaded shank, a mandrel shank, and a flange at a distal end thereof; a solid elastic annular bladder comprising a bore, an outer surface, a lower surface, and an upper surface, said bladder disposed upon said mandrel with said lower surface of said bladder in contact with said flange of said mandrel and said mandrel shank passing through said bore in said bladder; a compression flange comprising a compression washer and a compression collar, said compression washer comprising a lower surface in contact with said upper surface of said bladder, and said compression collar comprising a bore slidingly engaged with said threaded shank of said mandrel; and a compression nut threadedly engaged with said threaded shank of said mandrel, wherein when said compression nut is tightened upon said threaded shank, said solid bladder is compressed between said flange of said mandrel and said compression washer, causing said outer surface of said bladder to have an arcuate shape.
In accordance with the present invention, there is provided a polishing tool comprising a mandrel having a drive shank at a proximal end thereof, a threaded shank, a mandrel shank, and a flange at a distal end thereof; a solid elastic annular bladder comprising a bore, an outer surface, a lower surface, and an upper surface, said bladder disposed upon said mandrel with said lower surface of said bladder in contact with said flange of said mandrel and said mandrel shank passing through said bore in said bladder; a compression flange comprising a compression washer and a compression collar, said compression washer comprising a lower surface in contact with said upper surface of said bladder, and said compression collar comprising a bore slidingly engaged with said threaded shank of said mandrel; a polishing band engaged with said outer surface of said bladder; and a compression nut threadedly engaged with said threaded shank of said mandrel, wherein when said compression nut is tightened upon said threaded shank, said solid bladder is compressed between said flange of said mandrel and said compression washer, causing said outer surface of said bladder to have an arcuate shape.
In accordance with the present invention, there is provided a polishing tool comprising a mandrel having a drive shank at a proximal end thereof, a threaded shank, a mandrel shank, and a flange at a distal end thereof; a solid elastic annular bladder comprising a bore, an outer surface, a lower surface, and an upper surface, said bladder disposed upon said mandrel with said lower surface of said bladder in contact with said flange of said mandrel and said mandrel shank passing through said bore in said bladder; and means for compressing said lower surface of said bladder toward said upper surface of said bladder, thereby causing said outer surface of said bladder to have an arcuate shape.
The tools, apparatus, and method of the present invention are advantageous because they are simple and lower in cost compared to other approaches, and it can be adapted for the polishing of a variety of materials and shapes, particularly those objects having deeply concave shapes. As a result of the invention, articles of manufacture such as precision optics, injection mold inserts, and thin film coating dies can be polished with high precision at a high throughput and low cost.
BRIEF DESCRIPTION OF THE DRAWINGSThe invention will be described by reference to the following drawings, in which like numerals refer to like elements, and in which:
The present invention will be described in connection with certain preferred embodiments, however, it will be understood that there is no intent to limit the invention to the embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTSFor a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In describing the present invention, the following term(s) have been used in the description:
As used herein, the term figure error (or form error) is the measured global deviation from the desired surface shape e.g., a sphere, asphere or polynomial geometric shape.
As used herein, form error is a low frequency error. Traditionally in optics, irregularity and power are the two specifications that need to be considered. Irregularity is the deviation from a perfect surface. Power is the resulting average surface dimensions e.g., radius of curvature.
As used herein, the term zonal enhancement is meant to indicate a correction of the figure error, which is located symmetrically or asymmetrically at one specific location (zone) on the work piece. For example, if a cylindrical disc was the workpiece, a zonal error would be in one sector of the disc, or in a specific band or ring on the disc, or other rotationally symmetrical part.
As used herein, the terms spot, high, mid- and low spatial frequencies in reference to errors in a surface to be polished are meant to indicate the following. Low spatial frequencies are errors that appear only once to a few times across a particular surface. Mid-spatial frequencies are errors that occur many times across a surface of a part, generally have a periodic spacing of between 80 microns and 3 mm, and are typically caused by cutter marks due to machine or tool vibrations. High spatial frequencies are errors that happen on a microscopic scale, which may appear thousands of times across the surface of a part, and have a periodic spacing of less than 80 microns.
As used herein, the term polishing, when used in reference to a workpiece to be finished, is meant to indicate a chemo/mechanical process that ablates material from a surface.
As used herein, the term correction of form, or form error modification correction, when used in reference to a workpiece to be finished, is meant to indicate the same as has been defined for figure error.
As used herein, the term figure, when used in reference to a workpiece to be finished, is meant to indicate polishing in a correction for error in the figure and or form, which are the same.
As used herein, the term surface roughness, when used in reference to a workpiece to be finished, is meant to indicate high frequency errors, which are typically the result of brittle fracture regime (e.g.microcracks).
Workpiece spindle 108 is mounted upon linear slide 106, such that the motion of spindle 108 is bidirectionally programmable along axis 109, which is parallel to X-axis 107. Thus spindle 108 is movable by computer control along axis 109, depending on the requirements or the polishing process. Rotatable workpiece chucking device 110 is attached to end of workpiece spindle 108. The workpiece 10 to be polished is engaged and held by chuck 110 and rotated by spindle 108 around the central rotary axis thereof.
Apparatus 100 further comprises vertical slide 120 attached to polishing machine column 122, which is joined to base 102. The motion of vertical slide 120 is bi-directional along Z-axis 121. Polishing tool spindle 124 is attached to the Z-axis slide 120. The rotational speed (RPM) of this spindle is varied by the computer depending on the desired removal rate of material from workpiece 10. Apparatus 100 further comprises a rotatable chucking device 126 attached to the end of polishing tool spindle 124, in which polishing tool 128 of the present invention is inserted and rotated. Polishing tool 128 is provided in a variety of shapes, sizes, and materials (e.g. see polishing tool 200 of
In summary, there are three linear and one rotary axis drives in this configuration, all of which are computer controlled to allow for a deterministic polishing process, to be described subsequently in more detail in this specification.
Referring again to
In other embodiments, delivery system 130 delivers a homogeneous liquid substantially free of solid particles. Suitable liquids may be e.g. water, water soluble oils or lubricants (such as e.g. glycerine), hydrocarbon oils, silicone oils, and the like. The selection of a particular homogeneous liquid or a particulate slurry will depend upon the particular optical part being polished, and upon the desired end results.
Referring again to
End 210 of mandrel 202 has an axial bore 212 disposed therein, which is connected to at least one radial bore 214, or preferably a plurality of radial bores 214 extending to a cavity 216 disposed in the perimeter 218 of mandrel 202. Such axial bore 212 and radial bores 214 form a continuous passageway such that cavity 216 is in communication with the atmosphere outside of tool 200. Thus axial bore 212 and radial bores 214 allow the cavity 216 to be filled and pressurized with a fluid delivered through inflation device 220, which is disposed and sealed in axial bore 212 at the end 210 of mandrel 202.
Polishing tool 200 further comprises a ring assembly 230 of polishing material disposed around the outer perimeter of bladder 204.
Abrasive ring 234 is made of a material of sufficient structural strength to withstand the high shear and tensile forces during polishing, and to resist degradation through exposure to the polishing/lubricating fluid, such as e.g. polyurethanes of various durometers; and various types of felt, cork, and metal and/or resin bond diamond, alumina, and/or zirconium, with a multitude of different types of backings and patterns therein. Abrasive ring 234 preferably has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 2 millimeters and about 30 millimeters.
Referring again to
The tire-shaped bladder 204 may have a variety of specific cross sectional shapes. Before inflating bladder 204 with either air or some other fluid, polishing foil 203 is disposed around or applied to the bladder tool to act as the polishing medium. In one further embodiment, polishing foil 230 is made of polyurethane, and the abrasive polishing medium is provided in a liquid slurry that is pumped onto workpiece 10 and polishing foil 230, as described previously. Alternatively, abrasive particles may be embedded in the polishing foil. Suitable abrasive particles include particles made by the Rhodes Corporation, or by the Minnesota Mining and Manufacturing Company (3M). or it may actually be a product that has In a further embodiment, abrasive particles in the shape of miniature pyramids of polishing medium such as e.g., alumina in varying grit sizes is used. Such products will require that only water be added to wet the polishing medium (the dry powder.)
In another embodiment, foil 230 comprises a backer ring of poly(ethylene terephthalate) (PET) or similar material to allow softer polishing ring media to be used without tearing or pulling apart, yet maintaining the flexibility required for fine polishing. Bladder 204 of tool 200 is then inflated to a specific pressure depending on the polishing results desired. In such an embodiment, foil 230 is held in position upon bladder 204 by the expansion pressure of the bladder 204 being inflated; thus no adhesive or mechanism is required to bond foil 230 to bladder 204. Such a configuration enables a simple and rapid change of foil polishing media.
In operation of apparatus 100 of
It will be apparent that a variety of fluids may be used to pressurize bladder 204 of polishing tool 200, and that the physical properties of such fluids, as well as the pressure of such fluids also will affect the accuracy and removal rates of the polishing process. The fluid may be selected so as to beneficially affect the polishing process. In one simple and thus preferred embodiment, air is used as the bladder inflation fluid. In another embodiment, a much more dense fluid, i.e. a liquid, such as water is used as the bladder inflation fluid. In such an embodiment, the effective pressure of the outer wall of the bladder is a function of not only the inflation pressure, but also the rotational speed. Such rotational speed provides an additional pressure component due to the centrifugal force exerted by the fluid, in proportion to the square of the rotational speed. Such pressure is analogous to the pressure at the base of a column of liquid acted upon by gravity.
In a further embodiment, a viscous liquid, such as a hydraulic oil is used as a bladder inflation fluid. The viscosity of such a viscous liquid is preferably between about 10 centipoise and about 100,000 centipoise, and more preferably between about 20 centipoise and about 1000 centipoise. The higher viscosity of such fluid also affects the accuracy and removal rates of the polishing process, because at the contact area of the bladder with the workpiece, the bladder is deformed; hence the fluid disposed within the bladder must undergo viscous flow in this region. Thus a higher viscosity fluid has a greater resistance to deformation, and also being non compressible and thus can provide a beneficial polishing effect. In yet another embodiment, the use of a viscous fluid provides vibration damping to the process, thereby rendering such process more precise, stable, and reliable. In further embodiments, non-Newtonian fluids are used such as. e.g. a shear thinning fluid, or a shear thickening fluid. In other embodiments, fluids for which the rheology may be varied by exposure to an electric or magnetic field may be used.
Referring again to
It is to be understood that many multi-axis CNC machine tools are known in the art, which can be suitably configured to use the polishing tool and the methods of the present invention. The particular configuration of machine tool will depend upon the material properties, size, and shape of the starting blank and the desired finished end product. The present invention is not limited only to the use of the machine tools described herein. For example, such a machine tool could comprise from between two computer controlled axes up to as many as five or six computer controlled linear and/or rotary axes.
Referring again to
During the polishing operation, the polishing slurry/fluid suspension is fed between the polishing tool 200 and the work piece 10 by slurry delivery system 130. Depending on the results required, the axis traverse feedrates (i.e. the velocities of the linear slides), the workpiece rotational speed in revolutions per minute (RPM) and tool spindle rotational speed in RPM, and the tool path variation in three dimensional space are adjusted via automated computer control.
In one embodiment, the pressure (and thus the “firmness”) of bladder 204 of polishing tool 200 is preset, and maintained constant during the polishing operation. Depending on the bladder shape, the bladder material properties, the bladder inflation pressure, and the hardness/density of polishing foil 230, a specific pretest is performed in order to characterize the polishing spot profile. As used herein, the term spot profile is meant to indicate the indentation resulting from contacting a test workpiece with polishing tool 200 or 300 by moving the otherwise stationary test workpiece into contact with the polishing tool 200 or 300, thus leaving a depression, indentation, or “footprint” in the part the test is performed in a standard manner, with the workpiece moved against the tool with a specified displacement for a specified period of time. The resulting volume of the indentation per unit time period it the material removal rate.
Thus the shape and size of the area produced when the polishing tool is pressed into the test piece for a given period of time is the spot profile. This spot profile is then used in the generation of the time dependent trajectory of the polishing tool over the surface of the workpiece that is required to achieve the desired polishing results. This time dependent trajectory is also known in the art as the tool path and dwell times used in polishing. With the profile characterized, high, mid and low spatial features can be greatly improved through adjustments of the polishing variables, tool rpm, workpiece rpm, axes feedrates, and compression factor. As used herein, the term compression factor is meant to indicate the compressive force applied by the polishing tool against the workpiece, such force being the combination of force due to bladder pressure, and force due to the trajectory of the tool against the workpiece.
Referring again to
As was described previously, there are machine configurations for apparatus 100 that can be provided, depending on the workpiece shape and size, and the desired finished workpiece results. The motions of these axes may be combined so as to not only provide straight, linear, or arcuate motions of the polishing tool 200, but also to provide zigzag, sinusoidal, rotary or other programmable oscillations, in order to achieve the amount of material that is to be removed and to achieve the resulting surface quality.
Based on the configuration of the machine 100, the spindles and linear and/or rotational slides thereof, and the type/form or the polishing tool(s) to be used, there are various steps required in the process of the present invention, which results not only in the polishing of the workpiece, but also the correction of the surface errors/form of the workpiece.
In general, the pre-machined (i.e. unfinished) workpiece may be measured with a surface profilometer, an interferometer, a CMM or any other type of measuring device capable of analyzing the geometric shape, in order to quantitatively define the basic starting condition of the workpiece. This information is required to begin the process of improving the components surface roughness, mid-spatial frequency (waviness) and figure. After the analysis, the acquired data on the workpiece is then communicated into the computer control on the machine. This information, along with the software built into the computer control, calculates the process parameters/motion control required giving the desired workpiece improvements.
The polishing tool spot size and shape is either known based on a library of predetermined empirical parameters obtained experimentally, or it is analyzed through a series of tests. The polishing tool spot size and shape is then sent to the CNC controller. This data is the additional information needed to develop the required polishing tool path motion and speed, and spindle rotational and linear speeds to achieve the desired process results. It is to be understood that the polishing spot size may be affected by the size, shape, material properties, and fill pressure of the bladder, fluid type of the filled bladder, and the polishing foil material properties.
A more detailed description of methods for using the polishing tools and the apparatus of the present invention will now be described. It is to be understood that the steps in the following descriptions are illustrative of some embodiments of methods, but that the order of the steps described herein may be changed, while still achieving substantially the same end results. Thus, such variations in the methods described herein are to be considered within the scope of the present invention.
A first preferred step, based upon experience and knowledge of the finishing process and the previously described data obtained on the unfinished part, is to assemble and fit a polishing tool to the polishing apparatus.
The overall preparation/setup of the polishing apparatus then follows.
Machine setup process 420 continues with step 424, in which the polishing tool dimensional data obtained in measurement step 418 is entered into the CNC process controller of machine 100. The unfinished optic or other workpiece to be polished is then placed into holding chuck 110 of spindle 108 in step 426. The data obtained from measurements made on the unfinished optic that have been described previously are also entered into machine 100 in step 428. In step 430, an analysis of the spot size/removal function of the polisher on the optic is performed, or such data from a previously described library of tool functions is entered into the CNC process controller. In step 432, the CNC process controller is further programmed with polishing tool and polishing medium parametric data such as removal function, polishing spot size, polishing tool medium/material type, polishing tool dimensions/shape, polishing tool bladder pressure, optic/workpiece starting and finished dimensions, and polishing slurry type/composition.
With all of the relevant data programmed into the CNC process controller, the deterministic path of the polishing tool 200 on the optic 10 is calculated by such controller in step 434. In performing machine setup process 420, depending on the shape and size of the workpiece 10, coordinate offsets will be established in all of the programmable axes 104, 106, 108, and 120, so as to provide the CNC controller of machine 100 the information/location of part 100 such machine 100 will begin the polishing process at the correct location on workpiece 10. At this point, with machine setup 420 complete, some test probing of the workpiece 10 and/or the polishing tool 200 may be implemented to confirm that such starting location is correct. Once the CNC controller of machine 100 has defined/confirmed the “part zero” or starting position of polishing tool 200 upon workpiece 10, the polishing process may begin.
In some circumstances, more than one bladder-polishing tool may be required to achieve the desired results in polishing workpiece 10. Accordingly, in one embodiment (not shown), machine 100 is provided with automatic tool changers, to change between multiple polishing tools during the process. In another embodiment (not shown) multiple spindles are provided on machine 100, wherein a first polishing tool on a first spindle performs part of the polishing operation, a second polishing tool on a second spindle performs part of the polishing operation, and so forth, to the extent that multiple tools and spindles are provided on machine 100.
In the preferred embodiment of polishing cycle 440, but not in all embodiments, at such time when the spindles 108 and 124 have started, but before any motion of tool 200 along axes 105, 107, 109, and 121, there is provided and injection or pumping of a specific polishing slurry or other fluid at the contact location of polishing tool 200 with workpiece 10, which enhances the polishing action or removal rates of material from workpiece 10. As described previously, the path of the polishing tool 200 over the workpiece 10 may include straight, linear, arcuate zigzag, sinusoidal, rotary, spiral, or other programmable motions so as to enhance the removal rate of material from workpiece 10.
In performing polishing cycle 440 of process 400 of
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- 1. The rotational speed of the workpiece spindle 108 may be controlled to give the effect of constant surface speed of workpiece 10 similar to that of current CNC lathe technology, so as to maintain a constant removal rate of material from the workpiece 10. Such control of spindle speed eliminates the effect of the decreasing or increasing diameter of the contact circle made by the polishing tool 200 upon the rotating workpiece 10, as it will be apparent that the surface speed at the extremity (i.e. maximum diameter) of the rotating workpiece is much greater than the surface speed near the center of the workpiece. As the polishing tool 200 approaches the center of the workpiece 10, the surface speed approaches zero; thus such a variation in surface speed may be compensated for by varying the rotational speed of workpiece spindle 108.
- 2. The speed/position of workpiece 10 may also be controlled so as to improve rotational asymmetries of the workpiece during the polishing cycle 440. For example, if there is an asymmetry that requires more removal in a specific area of workpiece 10, then the part spindle may slow or even stop in this area so as to allow more removal by polishing tool 200. Alternatively, the opposite situation may occur wherein less material removal is required and the workpiece 10 may speed up during polishing in this area to minimize the removal. In other terms, the dwell time of the polishing tool 200 upon the workpiece 10 is adjusted to selectively decrease or remove rotational asymmetries.
- 3. The “stiffness” of the polishing tool may be preset based upon the inflation pressure within the bladder 204 of tool 200. Depending on how “hard” or “soft” bladder 204 is made by inflation pressure, the removal function of tool 200 will be affected. Typically a stiffer polishing tool (i.e. higher inflation pressure) will be used where higher removal functions are required such as in processes where form error modification of workpiece 10 is needed. Likewise, less inflation pressure will be applied to bladder 204 in a final finishing process where the best possible surface finish is required, at the expense of a lower material removal rate. In a further embodiment described previously, inflation pressure may be varied in real time during the polishing cycle 440.
- 4. The compression factor may also be controlled in the polishing cycle 440. Control of the compression factor is achieved through the CNC program wherein the path the polishing tool 200 is moved in a less compressed or more compressed path (“tighter” or “looser path”) over the part, thereby affecting its removal function and rate.
- 5. The tightness of the zigzag or circular motion of the polishing tool 200 in its path over the workpiece 10 may also be adjusted and varied throughout the polishing cycle 440. In one embodiment, the compression factor is held constant while the zigzag or circular motion of the polishing tool 200 is varied. Circular and other motions such as e.g., zigzag, provide better surface finish i.e. polish without leaving artifacts from the tool/abrasive slurry in the surface i.e., grooving.
- 6. The composition, Theological properties, PH, concentration, and flow rate of polishing slurry delivered to the polishing tool/workpiece during the process may be varied to affect removal rates and surface roughness.
- 7. The size, shape, and material properties of the bladder 204 of polishing tool 200 significantly affects the process results and capabilities depending on the workpiece 10 to be polished.
- 8. The material that the bladder is wrapped with (the foil 230) is another variable, which will also affect the material removal and finishing characteristics during polishing cycle 440.
- 9. The physical properties of the fluid medium used to pressurize bladder 204 of tool 200 may be varied. Such physical properties include specific gravity, shear viscosity, and extensional viscosity. Variation of such properties between the basic choice of a liquid or a gas is at least several orders or magnitude. However, there is significant variation between liquids, and there is opportunity for further control based on the use of non-Newtonian liquids, such as shear or extensional thickening liquids, shear or extensional thinning liquids, visco-elastic liquids, and/or magneto-rheological liquids.
Using variations of the process parameters described in 1-9 above, the removal rates, the surface roughness, mid spatial frequency errors and figure error will be optimized during polishing cycle 440. Upon completion of polishing cycle 440, the machine 100 of
If such optic is not acceptable against specifications, steps are taken to prepare for another polishing cycle 440. Such steps include step 460, reprogramming of the CNC controller; optional step 470 of setting up/installing/and/or changing to a new polishing tool; and step 480, calculation of a new deterministic path for the next polishing cycle 440. The second polishing cycle then proceeds as previously described, and further iterations of steps 450-480 and 440 occur until the optic is polished to a condition that is acceptable against specifications, at which time step 490 is performed.
Included within the scope of the present invention is another embodiment of a polishing tool for the polishing of concave surfaces.
Numerous other embodiments of tool 300 are possible, wherein bladder 304 is formed such that bladder 304 fully encloses the outer surface 309 of the distal end of mandrel 302. In one embodiment, bladder 304 is conical, as indicated by dotted lines 311. In other embodiments, bladder 304 may have a parabolic shape, a hyperbolic shape, or combinations and transitions between hemispherical, conical (linear), hyperbolic, and parabolic surfaces at different radial zones along the surface of bladder 304. Thus bladder 304 may have a precisely hemispherical shape, a precisely conical shape, or a generally curved or domed shape formed by some combination of these various surface definitions. It will be apparent that even in the instance of a conically shaped bladder 304, that such bladder will likely be formed with a slight radius at the apex of such cone.
Mandrel 302 is further provided with an axial bore 312 disposed from the outer end 324 of shank 301 through the center of flange 305, such that the outer end 324 of mandrel 302 is in communication with cavity 316. Polishing tool 300 further comprises an inflation device 320 such as e.g., a check valve, or a tire valve stem, for providing a means to pressurize cavity 316 and maintain pressure therein, as previously described for tool 200 of
It will be apparent that in embodiments in which a relatively dense fluid, i.e. a liquid is used, and in which an elastic bladder is used, that the overall profile of the bladder, and therefore the spot size, can be varied as a function of polishing tool rotational speed. At relatively low rotational speed, a bladder with a substantially hemispherical shape will maintain such shape. As rotational speed is increased, the centrifugal force acting on the liquid contained in the bladder will deform the bladder into a flattened dome profile having a large radius of curvature near the center of the bladder, and a small radius of curvature near the lip 303 of the bladder. Such a feature can be used in the process of the present invention, wherein the polishing spot size is rendered adjustable as a function of rotational speed.
Referring again to
It is to be understood that the machine 100 of
The overall computerized polishing process 400 using the apparatus 100 and polishing tool 200 of the present invention has many distinct advantages over prior art figure/polishing enhancement techniques, which are as follows:
-
- 1. There are numerous options available with respect to size and shape of the bladder attached to the tool, such as a tire shape, hemisphere shape, domed shape, conical shapes, cylindrical shape, and the like. The shape of the bladder chosen depends on the part geometry and the desired process results. There are also options available in the choice of material composition and properties of the bladder. These options of size, shape, and material composition render the process of the present invention very versatile.
- 2. Bladder inflation pressure is easily adjusted before the process begins and for many polishing process requirements, no pressure modification is required during the polishing process. In the event that it is desirable to adjust bladder pressure during the polishing process, a polishing tool and apparatus can be made to provide such additional process versatility.
- 3. The method of inflating the bladder into the polishing foil makes replacement of the foil very simple, and typically no adhesive or mechanisms are required for attaching the foil to the bladder. Adhesive is only required to attach the foil to the PET ring.
- 4. In using the polishing tools of the present invention, many types of materials may be wrapped around the bladder, thus allowing for the use of a wide variety of polishing foil media. Polishing foils may be made of e.g. polyurethanes, felts, synthetics, corks, leathers, and many other materials, depending on the desired polishing results. The foils may be impregnated with cerium, diamond, alumina, pitch, etc.
- 5. The preferred method of placing the ring or foil upon the bladder also allows for modification of the shape of the foil or ring, i.e. the width, radius/contour or thickness thereof.
- 6. In the preferred embodiment, the poly(ethylene terephthalate) ring that the foil may be attached to has not only great strength but also long lasting flexibility, which greatly extend the life of the polishing tool.
- 7. The concept of the bladder tool allows for flexibility so that the polisher can conform to a variety of workpiece surface geometries and still maintain contact/polishing action upon such surfaces.
- 8. In contrast to small spot polishing tools, the bladder polisher of the present invention will last and hold its shape much longer in operation. A polishing ring of material, and not just single spot develops the spot in the polishing tool and the process of the present invention, so the polishing surface area of the tool is greatly increased.
- 9. The compression amount and spot size of the polishing tool can be easily adjusted by modifying the computer program to move the tool closer or further from the part in its path over such part.
- 10. Because of the variety of shapes and types of materials that the various components of the polishing tool can be made from, the polishing process of the present invention has the flexibility to repair figure errors in a workpiece, and also achieve the highest surface quality requirements of such workpiece.
- 11. In instances where the process may require one or more polishing tools to achieve the final results, this is easily accomplished with known machine tool automatic tool changing technology or multiple spindle technology, depending on the configuration of the particular machine.
- 12. The powerful computer control algorithms provide the machine operator with a variety of flexible programs which, depending on desired results, can be easily modified and implemented, such as e.g., zigzag, circular, orbital, elliptical tool paths.
- 13. Polishing of steels and other metallic components, especially those used in injection molds, and thin film coating dies can be done without the current technological limitations of prior art polishing processes.
In another preferred embodiment, the polishing tool further comprises actuation means to engage and/or extend and/or position and/or compress the inflatable bladder or other compliant part, and any polishing foil disposed thereupon, with respect to the part to be improved or polished. Such actuation means may comprise one or more linear actuating devices such as e.g., air operated or hydraulically operated cylinders.
Referring to
Toward the proximal end 504 of base 502, drive wheel 510 is operatively joined or attached to rotatable shaft 512, which is disposed in a housing 514 joined to base 502. Housing 514 is preferably joined to base 502 by threaded fasteners (not shown) engaged with tapped holes (not shown) therein, or by other suitable means. Rotatable shaft 512 is preferably disposed within means for enabling precise rotation, such as e.g., a bushing, or more preferably, bearings 516.
Tool 500 further comprises a polishing wheel 520, which is joined to linkage 530. Linkage 530 is operatively attached to actuating means 540, such that actuating means 540 actuates linkage 530, and thus moves polishing wheel 520, as indicated by bidirectional arrow 599. This motion of polishing wheel 520 serves to engage a polishing foil with a portion of the perimeters of polishing wheel 520 and drive wheel 510; such engagement will be described subsequently in this specification.
In the preferred embodiment depicted in
Referring again to
Cylinder 542 is thus rigidly secured to base 502, and thus in the operation of the tool 500 (to be described subsequently in this specification), cylinder 542 linearly actuates polishing wheel 520 as indicated by bidirectional arrow 599. To accomplish such actuation, cylinder 542 is operatively connected to a pressurized fluid supply at ports 556 and 558 in the housing 545 thereof, preferably provided through flexible hoses (not shown). Such fluid supply is selectable and switchable, i.e. fluid pressure may be applied at port 556 and fluid vacuum may be applied at port 558 to actuate wheel 520 away from distal end 506 of base 502 and toward the work piece 112 (see
It will be apparent that actuating means 540 may comprise suitable linear actuators other than fluid pressure driven cylinders; many other linear actuators, such as rodless cylinders, stepper motors and other electromechanical actuators are well known and are to be considered within the scope of the present invention. Such linear actuators may be further provided with position sensing means, and/or position control means, and communication means for control thereof by an external process controller.
Tool 500 further comprises a polishing foil 680 (see
Polishing foil 680 is also shown in
Referring to
Belt 682 is formed of an elastic material. In one embodiment, belt 682 consists essentially of a band of poly(ethylene terephthalate) having a thickness of between about 50 microns and about 2000 microns, and a width of between about 7 millimeters and about 125 millimeters. In another embodiments, belt 682 consists essentially of elastomers such as e.g., gum rubbers, polyurethane, silicone and the like. Many other belt materials may be suitable, with the operative requirement being that belt 682 have sufficient elasticity to stretch when rod 544 of cylinder 542 is deployed as shown in
The abrasive ring 684 of foil 680 is made of a material of sufficient structural strength to withstand the high shear and tensile forces during polishing, and to resist degradation through exposure to the polishing/lubricating fluid, such as e.g. polyurethanes of various durometers; water resistant high strength cloth materials, and various types of felt, cork, and metal. Abrasive ring 684 further comprises abrasive particles embedded therein, or coated on the outer surface thereof, such as e.g. resin bonded diamond, alumina, and/or zirconium and the like. Abrasive ring 684 may have an inner surface having different types of backings, and/or patterns for engagement with belt 682.
Abrasive ring 684 preferably has a thickness of between about 1 millimeter and about 5 millimeters, and a width of between about 7 millimeters and about 125 millimeters. Additional operative requirements of abrasive ring 684 are that it have a greater circumference than belt 682, and that it is substantially inelastic, or significantly less elastic than belt 682, in order to enable proper engagement therewith.
The engagement of belt 682 with abrasive ring 684 is now described. Referring again to
As can be seen in
The rotation of drive wheel 520 in such circumstances thus results in the displacement of abrasive ring as indicated by arrows 593. Essentially, the actuation of cylinder 542 as indicated by arrow 599, in combination with the components attached thereto, acts as a clutch mechanism to engage and drive abrasive ring 684.
In another embodiment, polishing foil 680 may be formed as a unitary structure in a manner similar to ring 230 of
In order to have good function as a drive belt engaged with wheels, polishing foil 680 may be provided with features known in drive belt art, such as grooves (not shown) on the inner surface thereof (mated with corresponding grooves in wheels 510 and 520); or teeth (not shown) on the inner surface thereof (mated with corresponding teeth in wheels 510 and 520 as is done with timing belts and pulleys); or knurling or other textures on the inner surface thereof. Drive wheel 520 may further be provided with rims extending radially outward from the edges thereof for improved belt retention, as is commonly done with drive pulleys.
Polishing foil 680 may vary in length from about 4 inches for tools having pulleys on the order of 0.25-0.5 inches in diameter to about 50 inches for tools having pulleys on the order of 8 inches in diameter. The rotational speed of drive wheel 510 is provided such that the surface speed of polishing foil 680 is between about 2 and about 1000 inches per second, depending upon the particular polishing application. Polishing foil 680 may further comprise fiber reinforcements disposed therein, and may comprise woven or cloth-like material, provided that sufficient elasticity is provided as described herein.
Referring once again to
Thus tool 500 may be fabricated at a variety of scales, depending upon the particular application, and in particular, the size, shape, and degree of finishing required of the part to be worked. The diameters of drive wheel 510 and polishing wheel 520 may vary from about 0.25 inches to about 8 inches. The scale of the other components, i.e. base 502, cylinder 542, and linkage 530 would be sized as required to operate drive wheel 510 and polishing wheel 520 and the foil 680 engaged therewith. For example, cylinder 542 may be provided with a bore of between about 0.1 inch and about three inches.
Although it appears in the embodiment shown in
Polishing foil 680 may vary in width from about 0.25 to about 5 inches. The corresponding widths of drive wheel 510 and polishing wheel 520 thus vary in a similar manner in order to properly engage with and drive polishing foil 680.
The length of actuation stroke of means 540 (indicated by arrow 599) may vary from about 0.1 inch to about 3 inches, depending upon the scale of tool 500, and upon the degree of elasticity provided in polishing foil 680.
Referring again to
Referring to
Polishing wheel 520 may be formed of suitable elastomers such as rubber, polyurethane, or silicone, or a harder or higher durometer polymer. The selection of material for polishing wheel 520 will depend upon whether or not polishing wheel 520 is provided with a cavity therein for pressurization, the extent to which such cavity may be pressurized and thus deformed, and the desired tool spot size during the polishing operation. These variables have been described in detail in this specification with regard to tool 200 of
In other embodiments, and depending upon the particular object to be polished or otherwise finished, polishing wheel may be formed with a plano (cylindrical) surface, or a convex surface. Polishing wheel 520 may also be formed with circumferential grooves on surface 521, or axial grooves (such as e.g. a timing pulley), and/or a texture such as knurling. These various surfaces may be employed to improve the tracking and/or traction between polishing wheel 520 and foil 680, thereby preventing slippage therebetween. These various surfaces may be further employed advantageously in that such surfaces may be used to cause high frequency vibrations of polishing wheel 520 and foil 680 against the part to be finished, thereby enhancing the polishing effect of tool 500.
Referring to
Second cylinder 662 is joined at the proximal end thereof by shoulder bolt 667, which passes through bracket 663 and spacer 666, and which is threadedly engaged with a tapped hole in base 602. Second cylinder 662 also provides linear actuation of rod 664 and clevis 633 inwardly and outwardly from cylinder body 665 as indicated by bidirectional arrow 696. Since cylinder 662 is rotatable about shoulder bolt 667, this linear actuation of clevis 633 results in motion of the distal end of cylinder 642, and clevis 632 and polishing wheel 620 along a generally arcuate path as indicated by bidirectional arrow 695. This arcuate motion enables polishing wheel 620 and polishing foil 680 to be more effectively engaged with and compressed against the object to be polished, as will be subsequently explained with reference to
Referring again to
It is also noted that in the embodiment of tool 600 depicted in
In a further embodiment, there is provided the tool of
The fluid pressure applied to cylinder 642 and to cylinder 662 are among the parameters that determine the amount of force applied by polishing wheel 620 and foil 680 to the object 112, and which thus determine the tool spot size. Other parameters that determine such force and tool spot size are as described previously in this specification for tool 200 of
In addition to the polishing tools described herein, and in accordance with the present invention, there is provided an apparatus for polishing objects comprising a computer numerically controlled (CNC) machine in which is fitted one of the tools of the present invention as depicted in
Referring to
CNC machine 1000 further comprises vertical slide 120 attached to polishing machine frame or plate 123, which is joined to base 102. The motion of vertical slide 120 is bi-directional along Z-axis 121 as indicated by arrow 997. CNC machine 1000 is preferably provided with rotary axis 151, which is mounted upon vertical slide 120, and which is rotatable around B axis 152 (parallel to Z-axis 121) as indicated by bidirectional arrow 154. Polishing tool spindle 124 is attached to rotary axis 151. CNC machine 1000 further comprises a rotatable chucking device 126 attached to the end of polishing tool spindle 124, in which the drive shaft 612 polishing tool 600 of the present invention is inserted and rotated. Polishing tool 600 is positionable in a variety of orientations, several of which are depicted in
Referring now only to
Rotatable work piece chucking device 110 is attached to end of work piece spindle 108. The work piece 112 to be polished is engaged and held by chuck 110 and rotated by spindle 108 around the central rotary axis 109 thereof as indicated by arrow 996. This rotary motion of object 112 results in the surface motion thereof being orthogonal to the motion of the polishing foil 680 (see
Referring now only to
The motion of spindle 162 is bidirectionally programmable along the X axis 107 and the Y axis 105, both of which are perpendicular to the central axis of rotation 169 of object 112. To provide motion of tool 600 toward and away from object 112 in the direction of Z axis 121, rotary axis 151 and spindle 124 are rotated 90 degrees clockwise from their respective positions in
Referring now only to
In a further embodiment, the CNC machine 1000 is programmed to articulate tool 600 over the surface 115 of object 114 in a more complex path in X-Y-Z space. For example, tool 600 may be generally advanced along a linear path, but with a circular motion superimposed on such linear path. Such a tool path is known in the art as a trichordal path. Alternatively, and as described previously for the embodiments of
It will be apparent that many other apparatus configurations are possible in fitting the tools of the present invention to CNC machines to polish and/or grind and/or otherwise finish objects. Such CNC machines may have more or fewer linear and rotational actuators as required by the particular application.
It will be further apparent that the polishing methods described herein and depicted in
It will be apparent that there are many other apparatus configurations comprising actuation means that can increase the separation distance between two wheels, thereby providing increased tension of a belt engaged therewith; or that can increase the belt path length therearound (such as by an idler pulley), thereby providing increased tension of a belt engaged therewith, and that such actuation means are considered within the scope of the present invention. It will be apparent that there are many other apparatus configurations comprising actuation means that can adjust the position of a first wheel engaged to a second wheel by a belt, either along an arcuate path or a linear path or a combination thereof, and that such actuation means are also considered within the scope of the present invention.
In accordance with the present invention, another tool is provided that may perform similar polishing operations as those tools shown in
Solid bladder 730 has a generally annular shape and is fitted over mandrel 710 such that when assembled, bladder shank 714 of bladder mandrel 710 is disposed within inner bore 732 of solid bladder 730. Upper surface 734 and lower surface 736 of solid bladder 730 are in contact with the lower surface 742 of compression washer 740 and upper surface 717 of flange 718, respectively.
Compression collar 750 is slid over drive shank 711 of mandrel 710, and is positioned along mandrel 710 proximate to threaded shank 716; however, compression collar 750 is not engaged with the threads of threaded shank 716. Nut 760 is engaged with the threads of threaded shank 716 of mandrel 710, thereby applying an axial force against compression collar 750, and compression washer 740. Thus nut 760 can be tightened so that compression washer 740 and flange 718 of mandrel 710 to apply a compressive force against solid bladder 730 as indicated by arrows 799 and 798 (see
The assembly and preparation of tool 710 for polishing use will now be described. Such assembly and preparation is best understood with reference to
Solid bladder 730 is made of a highly elastic incompressible solid. Solid bladder preferably consists essentially of an elastomer having a Shore A durometer of between about 10 and about 90. Solid bladder 730 may be made of any suitable material which, when subjected to a compressive force, undergoes elastic deformation in a direction substantially orthogonal to such compressive force. For example, solid bladder 730 may consist essentially of gum rubber, nitrile rubber, or polyurethane. In a further embodiment, solid bladder 730 may consist essentially of an elastomeric closed cell foam.
In one preferred embodiment, solid bladder 730 is made of nitrile rubber having a Shore A durometer of about 40. Accordingly, when solid bladder 730 is compressed between compression washer 740 and flange 718 of mandrel 710 as indicated by arrows 799 and 798, the outer surface 739 of solid bladder 730 bulges outwardly as indicated by arrows 796. Referring now to
The outer surface 739 of solid bladder 730 assumes a generally arcuate shape simply due to the axial compression thereof, and the resulting radial expansion thereof. However, to achieve optimum polishing results of optics and the like, it is preferable that the arcuate surface 739 of compressed solid bladder 730 be ground or otherwise formed to a specified arcuate shape. To perform such a forming process, tool 700 is assembled as just previously described, with solid bladder 730 in compression and polishing band 770 not fitted to solid bladder 730. Setscrew 759 in compression collar 750 is fitted and tightened such that setscrew 759 engages in slot 713 in threaded shank 716 of mandrel 710 to the position indicated by engaged setscrew 759A shown in phantom in
The assembled tool 700 is then fitted into a precision lathe or other surface grinding machine, and arcuate surface 739 of solid bladder 730 is ground to a desired shape. In one preferred embodiment for the polishing of optics, arcuate surface 739 is ground to a spherical shape. By way of illustration, solid bladder 730 may have an uncompressed radius 795 of about 3.1 inches, a thickness of about 1 inch, and when compressed, a spherical arcuate surface 739 with a radius of about 4 inches and a thickness of 0.75 inches. It is to be understood that this radius of about 4 inches describes the radius of curvature of the surface 739 in the x-z through y-z planes, with z being the central axis 23A-23A (see
After surface 739 of solid bladder 730 is ground to the desired arcuate shape, tool 700 is removed from the surface grinder machine for the fitting of a polishing band to surface 739. To accomplish this, setscrew 759 in compression collar 750 is loosened slightly to allow setscrew 759 to slide in the axial direction (along axis 23A-23A) in slot 713 in threaded shank 716 of mandrel 710. Nut 760 is then loosened, and setscrew 759 slides in slot 713 until setscrew 759 butts up against the upper end 721 of slot 713. With setscrew 759 fitted in compression collar 750 and engaged with upper end 721 of slot 713, further axial travel of compression collar 750 is stopped.
Therefore, even if nut 760 is released further, solid bladder 730 remains in a state of semi-compression from that point on. Solid bladder 730 is thus preferably never totally released from its compression by compression washer 740 and flange 718 of bladder mandrel 710 after the finish grind is completed. A polishing band is then fitted around solid bladder 730, and nut 760 is retightened, engaging polishing band 770 with solid bladder 730, and forming polishing band 770 to the desired arcuate shape. Because of the provision of inner stop 755 in compression collar 750, which stops against shoulder stop 715, solid bladder 730 is compressed reproducibly to the same extent as when it was ground to the desired arcuate shape, and thus the curvature of arcuate surface 739 and polishing band 770 disposed thereupon is accurately reproduced.
Referring again to
It will be apparent that numerous other suitable means for locking the compression collar 750 or the combined collar 750/washer 740 as a compression flange 750/740 to mandrel 710 can be provided alternatively or additionally, such as e.g. a pin passing through collar 750 and threaded shank 716, or the keying of the shank 716 and the bore of collar 750, and the disposition of a piece of keystock in a key slot in one of shank 716 or the bore of collar 750. The arrangement depicted in the Figures herein is preferred, because it provides both rotational locking, and limited travel to maintain the bladder in semi-compression after precision grinding, while a polishing band is fit thereto.
In general, suitable materials for polishing band 770 are as described previously in this specification for the polishing tools described and shown in
It will be apparent that numerous other suitable means for compressing the lower surface 736 toward the upper surface 734 of solid bladder 710 and causing the outer surface 739 of said bladder to have an arcuate shape may be provided. For example, one may provide a pin cam assembly, or an assembly wherein a compression collar is rotated a small angular displacement such as a quarter-turn, compressing bladder 730 and then locking in place. Such assemblies may make use of one or more springs. In another embodiment, compression may be provided by one or more coil springs disposed on a shank portion of mandrel 710, with a circular disc and keepers engaged with such shank, in much the same way that valves are held in an automotive cylinder head.
It is, therefore, apparent that there has been provided, in accordance with the present invention, a tool for polishing objects comprising a wide variety of materials and shapes including precision optical surfaces and injection mold inserts. While this invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
Claims
1. A polishing tool comprising:
- a) a mandrel having a drive shank at a proximal end thereof, a threaded shank, a mandrel shank, and a flange at a distal end thereof;
- b) a solid elastic annular bladder comprising a bore, an outer surface, a lower surface, and an upper surface, said bladder disposed upon said mandrel with said lower surface of said bladder in contact with said flange of said mandrel and said mandrel shank passing through said bore in said bladder;
- c) a compression flange comprising a compression washer and a compression collar, said compression washer comprising a lower surface in contact with said upper surface of said bladder, and said compression collar comprising a bore slidingly engaged with said threaded shank of said mandrel; and
- d) a compression nut threadedly engaged with said threaded shank of said mandrel, wherein when said compression nut is tightened upon said threaded shank, said solid bladder is compressed between said flange of said mandrel and said compression washer, causing said outer surface of said bladder to have an arcuate shape.
2. The polishing tool as recited in claim 1, wherein said arcuate shape of said bladder resulting from said solid bladder being compressed between said flange of said mandrel and said compression washer is further ground to a different arcuate shape.
3. The polishing tool as recited in claim 2, wherein said different arcuate shape is a spherical shape.
4. The polishing tool as recited in claim 1, wherein said solid elastic annular bladder consists essentially of an elastomer.
5. The polishing tool as recited in claim 4, wherein said elastomer is selected from the group consisting of gum rubber, nitrile rubber, and polyurethane.
6. The polishing tool as recited in claim 4, wherein said elastomer has a Shore A durometer of between about 10 and about 90.
7. The polishing tool as recited in claim 6, wherein said elastomer has a Shore A durometer of about 40.
8. The polishing tool as recited in claim 1, wherein said solid elastic annular bladder consists essentially of an elastomeric closed cell foam.
9. The polishing tool as recited in claim 1, wherein said compression collar of said compression flange comprises an inner stop, and said mandrel comprises a shoulder stop, and wherein when said compression nut is tightened upon said threaded shank, said inner stop of said compression collar contacts said shoulder stop of said mandrel.
10. The polishing tool as recited in claim 1, further comprising means for locking said compression flange to said mandrel.
11. The polishing tool as recited in claim 10, wherein means for locking said compression flange to said mandrel comprises a setscrew in said compression collar engaged with said mandrel.
12. The polishing tool as recited in claim 1, further comprising a polishing band engaged with said outer surface of said bladder.
13. The polishing tool as recited in claim 12, wherein said polishing band comprises an outer surface impregnated with abrasive particles.
14. The polishing tool as recited in claim 13, wherein said abrasive particles are selected from the group consisting of ceria, alumina, silica, diamond, and mixtures thereof.
15. A polishing tool comprising:
- a) a mandrel having a drive shank at a proximal end thereof, a threaded shank, a mandrel shank, and a flange at a distal end thereof;
- b) a solid elastic annular bladder comprising a bore, an outer surface, a lower surface, and an upper surface, said bladder disposed upon said mandrel with said lower surface of said bladder in contact with said flange of said mandrel and said mandrel shank passing through said bore in said bladder;
- c) a compression flange comprising a compression washer and a compression collar, said compression washer comprising a lower surface in contact with said upper surface of said bladder, and said compression collar comprising a bore slidingly engaged with said threaded shank of said mandrel;
- d) a polishing band engaged with said outer surface of said bladder; and
- e) a compression nut threadedly engaged with said threaded shank of said mandrel, wherein when said compression nut is tightened upon said threaded shank, said solid bladder is compressed between said flange of said mandrel and said compression washer, causing said outer surface of said bladder and said polishing band to have an arcuate shape.
16. The polishing tool as recited in claim 15, wherein said polishing band comprises an outer surface impregnated with abrasive particles.
17. A polishing tool comprising:
- a) a mandrel having a drive shank at a proximal end thereof, a threaded shank, a mandrel shank, and a flange at a distal end thereof;
- b) a solid elastic annular bladder comprising a bore, an outer surface, a lower surface, and an upper surface, said bladder disposed upon said mandrel with said lower surface of said bladder in contact with said flange of said mandrel and said mandrel shank passing through said bore in said bladder; and
- c) means for compressing said lower surface of said bladder toward said upper surface of said bladder, thereby causing said outer surface of said bladder to have an arcuate shape.
18. The polishing tool as recited in claim 17, wherein said means for compressing said lower surface of said bladder toward said upper surface of said bladder comprises a compression flange comprising a compression washer and a compression collar, said compression washer comprising a lower surface in contact with said upper surface of said bladder, and said compression collar comprising a bore slidingly engaged with said threaded shank of said mandrel; and a compression nut threadedly engaged with said threaded shank of said mandrel.
Type: Application
Filed: Oct 12, 2004
Publication Date: Apr 14, 2005
Inventor: Michael Bechtold (Ontario, NY)
Application Number: 10/963,189