FIELD OF THE INVENTION

The present invention relates to techniques and principles used in Astronomy and high-precision Optics, as well as development of tooling that allows carrying out from a corrective grinding to high precision polishing on surfaces requiring high optical quality, and more particularly, the invention relates to a mixer module for a deterministic hydrodynamic tool for pulsed polishing of optical quality surfaces, as well as a method for carrying out pulsed polishing.

BACKGROUND OF THE INVENTION

The process of optical quality polishing, fine or high-precision polishing consists of roughing the surface material to be polished to smooth it, and to correct its figure with wavelength fraction accuracies.

In the field of high-precision optics and microelectronics, and more specifically, in terms of optical flattening of semiconductor surfaces, high-precision grinding and polishing is carried out with different modern techniques.

Conventional polishing methods, also known as classical polishing methods (R. N. Wilson “Reflecting Telescope Optics II, Manufacture, Testing, Alignment, Modern Techniques” Springer Verlag, 1999. and Wilson S R, et al., SPIE Vol. 966, 74, 1988) mainly use contact tools made of elastic materials (pitch, polyurethane, and the like) that precisely mold to the surface to be polished, exerting friction through an abrasive suspension layer. These polishing procedures tend to be artisanal and slow, and deform polishing tools due to temperature and torsion generated during the process, with a consequent tool wear where abrasive and removed material are embedded. Furthermore, conventional polishing methods have other disadvantages, such as: high hardness materials are only possible to work with; surfaces to work are deformed by pressure exerted on them by tools requiring rigid supports for them; they tend to leave a fallen edge due to semi-rigid contact material and the lack of support of the tool on the edge; the size of the tool is necessarily changed to make zonal corrections; they work with harmonic machines not having the advantages of a machine with several degrees of freedom as required, for example, for polishing of an off-axis surface.

Methods disclosed above were overcome by using “stressed lap” type tools, consisting of tools that actively deform to polish spherical surfaces more easily. However, such are complex methods and one of their important limitations is that precision working on surface edges is not possible obtaining what is known in the field of optics as fallen edge surfaces.

The state of the art shows other more updated methods than those already disclosed, which are used for optical surface fine polishing, namely: polishing by means of an ion gun (Ion Beam Figuring, which is an excellent method for correction of errors on an optical surface also known as “corrective polishing”); polishing by means of magnetorheological fluids; and polishing by fluidic jets (Fluid Jet Polishing). Characteristics and limitations of each are described below:

Polishing by means of an ion gun is described in U.S. Pat. Nos. 5,786,236 and 5,969,368, where said technology is based on bombardment of a surface to be polished with a collimated ion beam of inert gas thus producing material removal. This technology only allows fine polishing of a previously prepared and polished surface. Process is iterative based on an error map of the work surface which corrects imperfections. This method requires a vacuum chamber, at least the size of the piece to be polished, thus being expensive and complex; performing optical interferometric tests is not possible during the polishing process which complicates the iterative polishing/testing process; surface micro-roughness remains practically intact due to orthogonal beam incidence on the surface.

Polishing method by means of magnetorheological fluids is described in U.S. Pat. Nos. 5,971,835 and 6,106,380, consisting of confining a magnetic fluid with abrasive on a rotating cylinder perimeter area which is hardened under the influence of a magnetic field generating a polishing tool. Polishing is achieved by controlling the part to be polished on the magnetorheological fluid circulating on the rotating cylinder. Another variant of this method is to collimate an abrasive magnetorheological liquid flow by means of a magnetic field making it collide with the work surface.

On the other side, fluidic jet polishing (Booij, S. M., et al., Optical Engineering, August 2002, vol. 41, No. 8, pp. 1926-1931 and Booij, S. M., et al., I. OF&T conference, Tucson, June 2002, pp. 52-54. and O. Fáhnle at al., Appl. opt. 38, 6771-6773-1998) is the first fluid-based polishing technology, grinding the surface to be polished by an abrasive fluid beam. Jet is directed to the surface through a nozzle placed at certain angle and distance from the work surface. This polishing method has limited characteristics because generated erosion footprint is very small and generates low removal rates. Surfaces that can be worked are small and the tool is limited to meet the needs of high precision polishing in the fields of large surface optics.

On the other side, the state of the art also identifies Mexican Patent No. 251048 belonging to same inventors as in present patent application, which describes a useful tool for fine or high-precision grinding and polishing of flat and curved optical surfaces, including edges, as well as for optical flattening of semiconductor and metal surfaces without coming into contact with them, exerting zero force on work surface, where said tool was developed to solve problems that available technology had not solved at such time because in addition to above discussed limitations, each of the polishing and grinding methods showed another significant limitation related to the fact that the use of more than one technology to achieve a high precision finish on a surface was essential.

Said hydrodynamic tool has no moving parts and is arranged by interchangeable modules, namely a mixer module mixing two or more components of a polishing substance to form an abrasive foam and including a porous cavity to control density of said abrasive foam; a module of at least one rotational acceleration chamber having an optimized hydrodynamic geometry and including a set of power injectors in its periphery; an aerostatic suspension system generating a fluid layer where tool floats on, and said fluid layer allows said tool to adjust its position with respect to the work surface by means of a series of aerostatic bearings; a throat actuator; an exit nozzle; a diverging radial nozzle; and, a material recovery ring.

In the mixer module, a high velocity flow (abrasive foam) is produced which when leaving the hydrodynamic tool, radially and in parallel expands on the work surface creating an annular abrasion, stable, uniform and repeatable footprint. Its design allows carrying out the processes to obtain a very high precision optical surface, from corrective grinding to fine polishing without a need of changing tools, avoiding friction against the work surface, wear and deformation thereof, allowing also polishing of thin membranes without requiring rigid or active supports for the work piece.

However and despite its versatility, the hydrodynamic tool of Mexican patent '048 shows a limitation of not being able to interrupt its erosive action during the polishing process due to its internal hydrodynamic geometry. Interrupting supply of the polishing solution causes the tool to lose its stability and buoyancy, forcing it always turned on, which forces sweeping of the entire surface and always removing material. This reduces polishing process overall efficiency as erosion will be always present even in areas where polishing is not necessary, forcing process times higher than necessary, as well as excessive removal of material. This is disadvantageous for work on large surfaces where times can be tens of hours per run, and where polishing should not be interrupted by splicing footprints that are generated.

In order to solve the limitations of the hydrodynamic tool, internal arrangement of the mixer module in which the foaming step is carried out has been modified, so that supply of polishing solution can be interrupted without process operational stability being lost, allowing polishing by “poxel” (Polishing Element) that, together with hydrodynamic tool advantages possessed by Mexican patent '048, results in a much more competitive tool in the sense of obtaining a more efficient convergence towards the intended surface, also being capable of performing pulsed polishing actions which said hydrodynamic tool of the state of the art cannot achieve.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a mixer module arranged to be able to interrupt supply of abrasive foam or fluid without losing polishing process and hydrodynamic tool operational stability. What is intended is that said abrasive fluid remains inside the polishing tool less than one millisecond and once the flow is cut off, high internal velocities of pressurized gases are used to empty said tool, where said mixer module comprises: at least one high-velocity fluid interrupter element that can be disposed inside or outside the body of said mixer module, which function is to interrupt supply at controlled pressure and flow of abrasive foam; a first inlet through which pressurized air is injected under control; a second inlet through which a polishing fluid is controlledly injected which in the preferred embodiment of present invention is an abrasive polisher water suspension, wherein said polishing fluid fills a previously calculated volume in a suitable manner which is transferred to a mixing zone and in conjunction with the pressurized air, an abrasive foam is produced then injected into the module of the at least one rotational acceleration chamber of the hydrodynamic tool.

Density of abrasive foam depends on the pressure ratio with which air is injected on one side and the polishing fluid on the other side. Ensuring that abrasive foam dwell is less than one millisecond within this mixing step is important.

In a further aspect of present invention a method for carrying out the deterministic polishing process is also described by using the deterministic hydrodynamic polishing tool having coupled the mixer module of present invention, comprising the steps of: (a) generating an error map of the work surface to be polished from an interferogram; (b) generating a dwell time/pulse duration map of the deterministic hydrodynamic polishing tool for each position on the surface to be polished; (c) obtaining, in conjunction with the influence function or specific erosion footprint for each polishing tool, a movement map for a polishing robot allowing sweeping said work surface to be polished to obtain the desired optical figure; (d) carrying out the deterministic pulsed polishing on the work surface being able to use more than one hydrodynamic polishing tool simultaneously and mounted on a machine or several independent machines and in different arrangements; and, (e) generating a new error map of the polished work surface, and when necessary, repeating steps (a)-(d) until obtaining the desired optical figure.

Capacity of the mixer module to interrupt the supply of abrasive foam allows the hydrodynamic tool implementing a series of new polishing techniques that increase efficiency and overall performance of polishing with such tool, such as: pulsed polishing; zonal polishing; pulse width modulation (PWM, acronym for Pulse Width Modulation)); tessellation polishing; pixel polishing; interruption of the polishing run; edge polishing; convergence; multiple head polishing.

Likewise, the mixer module to be coupled to the deterministic hydrodynamic tool allows the possibility of carrying out several possible arrangements to accommodate multiple tools for simultaneous polishing, such as: multi-tool polishing in linear arrangement; multi-tool polishing in matrix arrangement; multi-tool polishing in spiral arrangement, and multi-tool polishing in one or more machines using above cited arrangements and other arrangements.

OBJECTS OF THE INVENTION

Taking into account the limitations found in the state of the art, an object of the present invention is the provision of a mixer module to be coupled to a deterministic hydrodynamic tool which optimized hydrodynamic geometry allows pulsed polishing of optical surfaces, as said tool is provided with the ability to instantly interrupt the abrasive effect, but without losing stability of operation parameters and tool buoyancy.

Another object of the present invention is to provide the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces, making said tool even more versatile and efficient since, besides allowing polishing only in those areas where correcting the surface is necessary but without having to travel the entire optical surface and remove material where not necessary, allows resuming the polishing process after being interrupted for any reason, eliminating “scars” generated by the inability to make a good splice.

A further object of present invention is to provide the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces, allowing to carry out said pulsed polishing by tessellation (or by sectors), since polishing paths can be spliced without leaving a footprint.

Still a further object of present invention is to provide the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces allowing polishing adjacent areas with one or more hydrodynamic tools without leaving a footprint or scar by means of polishing tessellation that optimizes the splice path.

Still another object of present invention is to provide the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces, where the pulsed polishing in turn allows simultaneously attacking a surface with several hydrodynamic tools at a time, with independent polishing action for each of them, reducing considerably polishing time of said surface and increasing process overall efficiency.

Even another object of the present invention is to provide the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces that allows linearly modulate the erosive process, since, unlike the hydrodynamic tool of radial flow found in the state of the art, with the mixer module coupled to said hydrodynamic tool from the error map of the surface to be polished, a velocity map is calculated to correct the surface and, starting from the error map, a time map with different pulse duration is calculated, so that pulse duration determines volume removed by “poxel”.

Still another object of the present invention is to provide a method for carrying out a deterministic hydrodynamic pulsed polishing, using the hydrodynamic tool coupled to the mixer module of the present invention.

Above objects, as well as other objects not described, features and advantages of the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces of present invention will be apparent for a person skilled in the art from the detailed description of certain embodiments and attached Figures, in addition to the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

Novel aspects that are deemed characteristic of the present invention will be particularly established in the appended claims. However, the invention itself both by its organization and its method of operation, together with other objects and advantages thereof, will be better understood in the following detailed description of embodiments of the present invention, when read in connection with the accompanying drawings wherein:

FIG. 1 is a graphic representation of a mixer module coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces, which has been built in accordance with a particularly preferred embodiment of the present invention.

FIG. 2 is a graph showing the results of Erosion vs. Pulse width.

FIG. 3 illustrates a pixelated pattern where a constant velocity of 2000 mm/min was maintained and alternating the erosive process between turned off/on with a 5 Hz frequency.

FIG. 4 illustrates a zonal pulsed polishing, where an isolated region in need of more polishing has been identified, such that a dampening band of constant width surrounding it is defined, which minimum width corresponds to the size of the erosion or poxel footprint.

FIG. 5 illustrates a plurality of deterministic hydropneumatic tools having the mixer module coupled to allow pulsed polishing to be carried out, and said hydrodynamic tools are mounted on several independent polishing robots.

FIG. 6 illustrates various images obtained with tessellation polishing, where left column images show the paths to follow for a rectangular “raster” polishing (upper) and for a tessellated polishing (lower); central column images show a splice simulation for both paths; and right column images show surface interferograms polished with both methods.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

For purpose of giving more clarity and understanding to the present description, a small glossary of terms that have been and will be used throughout this document are set forth below:

Generation: Shaping a 3D surface (usually a mathematical equation) on a solid object by means of rigid, flexible or fluidic abrasive tools (final error ˜100 μm).

Grinding: A process after generation consisting of removing surface material from any solid by means of friction, cutting or by high-hardness microscopic solid particle impact (final error of 1-10 μm).

Polishing: Final finish of a specular surface where surface error and roughness are less than 20 nm.

Fine polishing: Final finish of a specular surface where surface error and roughness are both less than 10 Angstrom.

Stability: Ability of the tool of the present invention to keep erosion footprint constant during its operation.

Repeatability: Ability of the tool of the present invention to keep erosion footprint constant during several operating cycles.

Uniformity: Ability of the tool of the present invention to keep erosion footprint constant along the ring.

Deterministic Process: A process where the same input parameters to a system will invariably produce the same outputs or results not involving randomness or process uncertainty.

Tessellation: Regularity or pattern of figures completely covering a surface that meets two requirements: i) no remaining spaces; and, ii) Figures do not overlap.

Pulse-width modulation: Pulse-width modulation (PWM) of a signal or power source is a technique wherein duty cycle of a periodic signal is modified to control the amount of abrasive power with which a surface is polished;

Poxel: {polishing element) Unit of area corresponding to erosion footprint size of the tool and defining the maximum spatial resolution with which a surface can be polished.

Important to remark is that the hydrodynamic tool described in Mexican patent '048 carries out three operative stages that rotationally accelerate the abrasive foam generated in the mixer module and that is radially expelled on the work piece, creating a grazing erosive action from abrasive particles that removes material. Rotation of the abrasive foam, accelerated by the action of acceleration chamber tangential injectors in conjunction with nozzle divergent geometry creates a vortex with a low pressure central area surrounded by a high pressure region cancelled each other over the work surface (300). As a result, the tool floats on said work piece and does not exert any net force on the surface to be polished. In addition, this buoyancy capacity self-aligns the tool in parallel to the surface to be polished, giving it a self-adjusting capacity. The ability to expel the abrasive foam at high velocity and in grazing way generates high removal rates, as well as low residual roughness and generating zero force on the surface (300) to be polished.

However, as discussed in the background section, said hydrodynamic tool of '048 patent works continuously, that is, it always remains turned on when in use and does not allow interruption of its erosive action during the polishing process, forcing to sweep the entire surface, and therefore, removing material where not necessary to do so, since, in case of interrupting supply (which is done alternating the On/Off switch) of the abrasive foam cavitation effects are caused that prevent the tool from restarting its operation once abrasive foam supply has been interrupted, therefore losing its stability and buoyancy.

In order to solve above problem, arrangement of the mixer module of the hydrodynamic tool is redesigned in such way that polishing fluid or abrasive foam flow can be interrupted without said tool losing stability during its operation.

In view of the foregoing, a new mixer module (100) was designed and developed to be coupled to a deterministic hydrodynamic tool (200), and more specifically, to the hydrodynamic tool described and claimed in Mexican patent '048; said mixer module (100) has the ability to instantaneously interrupt the abrasive effect, but without said hydrodynamic tool (200) losing stability of operating parameters, further increasing its versatility and efficiency, as polishing just in regions where necessary is allowed, correcting a work surface (not shown in the Figures) without the need to completely cover said surface, avoiding removing material where not necessary.

Mixer module (100) is arranged to be able to interrupt abrasive foam or fluid supply without losing process operational stability and the tool (200) can operate in pulsed mode carrying out polishing by “poxel”. What is intended is that said abrasive fluid remains inside the polishing tool (200) less than one millisecond and once the flow is cut off, high internal velocities of the pressurized gases are used to empty said tool (200).

With reference to FIG. 1 of the accompanying drawings, the hydrodynamic polishing tool (200) is graphically illustrated, and more specifically, the mixer module (100) (indicated by dashed line), which is described in accordance with a particularly preferred embodiment of the present invention and generally comprising: at least one high-velocity fluid interrupter element (10) that can be arranged inside or outside the body (20) of said mixer module (100), which function is interrupting supply at controlled flow and pressure of the abrasive foam, in the present invention the use of, but not limited to, a high-velocity solenoid valve as a interrupter element (10) is preferred, as any other device allowing rapid pulsation of fluids may be used such as electromechanical, piezoelectric, fluidic, or pneumatic, and the like; a first inlet (30) through which pressurized air is injected under control; a second inlet (40) through which a polishing fluid is controlledly injected which in the preferred embodiment of the present invention is an abrasive polishing water suspension, wherein said polishing fluid fills a previously calculated volume (50) and arranged to optimize the internal hydrodynamic geometry of the mixer module (100) and to reduce the polishing fluid dwell time in said volume for less than 1 ms so as not to lose the operating parameters and self-supporting capacity of the tool (200), and wherein said polishing fluid is transferred to a mixing zone (60) and, in conjunction with the pressurized air, an abrasive foam is produced which is injected into module (210) from the at least one rotational acceleration chamber of the hydrodynamic tool (200).

Density of abrasive foam depends on the pressure ratio with which air on one side and polishing fluid on the other side are injected. It is important to ensure that abrasive foam dwell is less than one millisecond within this mixing step.

Special care has been given to mixer module (100) hydrodynamic geometry being able to turn it on and off at high velocity without losing stability conditions that produce the self-support of the tool on the work surface (300).

Pulse duration is controlled by at least one interrupter element (10) to obtain a deterministic material removal. Erosion is proportional (linear) to pulse duration of the polishing fluid. Erosion is now a proportional (linear) function to pulse duration, allowing polishing with pulse width modulation (PWM) mode, obtaining roughing resolutions of up to 1 Å/ms (0.1 nm/ms). This action makes possible to precisely polish a finite surface element the size of the tool erosion footprint.

In a further embodiment, the present invention describes a method for carrying out the deterministic polishing process using the deterministic hydrodynamic polishing tool (200) having coupled the mixer module (100) described above, comprising the steps of:

(a) generating a work surface (300) error map to be polished from an interferogram, thus using, but not limited to, an interferometer, while any other high resolution metrological instrument can be used;

(b) generating a dwell time/pulse duration map of the deterministic hydrodynamic polishing tool for each position on the surface to be polished (300);

(c) obtaining, in conjunction with the influence function or erosion footprint particular to each polishing tool, a movement map for a polishing robot allowing sweeping said work surface to be polished (300) to obtain the desired optical figure;

(d) carrying out the deterministic pulsed polishing on the work surface (300), being able to use more than one hydrodynamic polishing tool simultaneously and mounted on the same machine or several independent machines and in different arrangements; and

(e) generating a new error map of the polished work surface (300), when necessary, repeating steps (a)-(d) until obtaining the desired optical figure.

For most of current polishing methods, including the tool described in Mexican patent '048, a velocity map is required that sweeps the tool over the surface, varying the velocity on each point, depending on the amount of material that must be removed. For the specific case of said Mexican patent '048 tool, as it cannot be turned off during the polishing process, polishing process efficiency is limited in the sense that there is always a minimum material removal (other than zero) associated with the maximum velocity at which the tool may be swept with the polishing robot. With the hydrodynamic tool (200) coupled to the mixer module (100) described in present invention, erosive action of the tool (200) may be interrupted thus allowing the pulsed polishing of a surface, with which a linear erosion function may be generated where removal is no longer a function of the polishing robot sweeping velocity (CNC, acronym in English of Computer Numeric Control), but of the pulse duration on each surface point, thus allowing generating dwell time maps with high precision removal rates from zero to the maximum removal obtainable with the tool, at constant sweep velocity. This new capacity of the hydrodynamic tool (200) allows implementing a series of new polishing techniques that increase efficiency and general performance of polishing with this tool, as described below:

Pulsed Polishing

Modification in mixer module (100) arrangement that is coupled to the hydrodynamic tool (200) allows generating polishing pulses that may be implemented either as individual pulses equivalent to polishing per unit area (poxel), or as a continuous tool sweeping (200) at constant velocity, varying pulse width and using pulse width modulation (PWM) techniques. This allows generating removal from zero up to maximum removal rate allowed by the tool (200). The fact that erosive action of said tool (200) may be pulsed leads to a linear process, where removal (moving the tool (200) at constant velocity) is a function of the turn-on time of the tool as shown in FIG. 2 of the accompanying drawings.

Zonal Polishing

When correction of a zone of the work surface is only necessary, in the case of polishing with the tool of the Mexican patent '048 crossing the surface with the tool turned on to the zone in question is necessary, leaving unintended approach footprints as well as input and output footprints in the zone to be polished. While, as previously mentioned several times, this problem is solved by pulsating the abrasive effect (200) of the tool having the mixer module (100) coupled, that is, the tool (200) is approached operating it with Y=0 until reaching a constant width dampening band that surrounds the area of interest. When tool (200) enters the dampening band, its velocity begins to change smoothly until reaching the required value in the region of interest. Within the area of interest the erosive action of said tool (200) is turned on and polishing by using any of the methods, or combination of methods as described below is possible, for example, pulse width modulation (PWM) method, tessellation or continuous polishing.

Modulation by Pulse Width

The new linear arrangement of the mixer module (100), allows controlling erosive pulse duration as a fraction of the time taken by the tool (200) to travel the distance equivalent to the size of its erosion footprint. Depth h of the material removed for a path is given by

$h - \frac{D_{v} Y}{VS}$

where Dv is the volumetric removal ratio (characteristic of each tool), Y is the working cycle of the PWM pulse width (the time divided by T), V is the velocity of the CNC and S is the size of the travel step.

On/Off period of signal is T=D/V where D is the diameter of the polishing tool footprint, such that in the time taken to travel the footprint diameter there is a pulse which duration may be varied from zero to the equivalent time to travel the footprint width at a given sweep velocity.

Depth h=βτ of removed material is proportional to dwell time of tool _T, where τ=YD/V, with β=Dv/SD. For the case of Y=1, the classic or continuous removal case is shown (Mexican patent '048) and roughing is controlled with the CNC sweep velocity.

In pulsed mode, where Y<1 roughing is controlled by the pulsed supply of abrasive foam in combination with the sweep velocity. In continuous mode, the minimum possible removal of material is limited by the maximum CNC velocity. To obtain minor removals, polishing by pulse width should be used.

For the case in which the duty cycle is varied between 0 and 1, at constant CNC velocity, creation of a pixelated pattern is possible that may be used to determine the tool response function (200).

Tessellated Polishing

For large surface polishing (larger than one meter), tool efficiency of Mexican patent '048 is limited by the size of the erosion footprint, as well as by the roughing volumetric ratio of the tool itself. However, any increase in process efficiency is possible by simultaneously polishing the surface with various hydrodynamic tools (200). This new polishing method in addition to allowing the combination of independently polished adjacent zones, eliminating splice footprints between them, allows polishing simultaneously a surface with several hydrodynamic polishing tools (200), where each of said tools (200) includes coupling the mixer module (100), decreasing the processing time according to the number of tools (200). Each polishing tool (200) would be mounted on a robot, as shown in FIG. 5 of the accompanying drawings, or instead, articulated arms (serial) or parallel robots (hexapod), or also one or several robotic arms with multiple heads in linear, matrix or spiral arrangements. Moreover, any numerical control machine that allows simultaneous polishing with several tools on a surface.

Tools (200) may be mounted on independent polishing robots (CNC), where each robot covers polishing of a certain section of the surface. This method has several drawbacks, such as obtaining non-smooth overlapping areas, as well as collision between tools when approaching while polishing adjacent areas.

In order to obtain smooth splicing footprints between two independent polishing zones, approaching the boundary between zones is necessary by following special paths, which have been termed as tessellated paths (refer to FIG. 6 of the accompanying drawings). This path form avoids duplicating dwell time in the splice area, as for example, in the case of a square or rectangular “raster” sweep pattern.

Another possibility is varying pulse width of each tool in the overlap zone, so that the combined dwell time is as required in such area to obtain a smooth splice.

In case where two independent paths match in time at a point on the boundary between zones, deceleration of one of the tools (200), turning it off and waiting for the other tool (200) to complete its sweep in this area and then re-starting the first tool (200) to continue with its polishing path is possible.

As illustrated in FIG. 6 of the accompanying drawings, images in the left column show the paths to be followed for rectangular “raster” polishing (upper) and for tessellated polishing (lower); images of the central column show a simulation of splices for both paths; and images in the right column show polished surface interferograms with both methods. The upper image set shows splicing of two independently polished surfaces using a rectangular sweep pattern, the upper right image shows how the overlap zone as well as the input footprint are very apparent. The lower image set shows an example of a sweep path incorporating a tessellated path in the splice area, in the lower right image the splice zone is not apparent.

Pixel Polishing

In the case of polishing by pulse width modulation (PWM) at constant velocity, the polishing response function in the sweep direction is different from that of the direction perpendicular to sweep direction. To obtain a symmetric response, the use of a method of polishing by pixel or discrete polishing is possible, which consists of moving the tool (200) to discrete positions among themselves, covering the region of interest with the same step increment in both axes. For each position, the tool (200) is turned on for the time necessary to obtain the desired removal. This method is useful for areas where very localized polishing is required, allowing following either a raster type sweep pattern, or any path or set of discrete positions on the region of interest.

Interruption of the Polishing Run

With the option of being able to turn on and off the erosive effect of the tool (200) by means of the mixer module (100) at any place and time of the polishing process, an interruption of the polishing process and continuation at any other time is possible.

Edge Polishing

Similarly to other polishing techniques, polishing with Mexican patent '048 tool leaves sagged the surface edges to be polished, with a width corresponding to the erosion footprint diameter of the tool. Said problem is solved by increasing tool velocity when approaching the rib, reducing the dwell time and therefore, the amount of material removed in that region to adapt it to the necessary amount; however, this may generate control problems in CNC, since the tool is accelerated in a region where a change of direction should be prepared, for example, if a raster-type sweep pattern is followed.

The ability to pulse the tool (200) allows this problem alleviation, since dwell time may be controlled without a need to increase tool velocity on the surface edge to be polished. In fact, this method allows decelerating CNC in preparation for a change of direction.

Convergence

An additional advantage of pulsed polishing is to converge more quickly towards the desired surface. In the case of polishing with Mexican patent '048 tool the imposition of having to remove a minimum quantity other than zero due to impossibility of turning off the tool erosive power, limits the amount of material that may be removed in each polishing run. While pulsating the tool (200) an absence (zero) of material removal and an increase in convergence ratio are possible.

Polishing with Multiple Heads

Since tool erosive process may be pulsed, mounting of multiple tools (200) on a common robotic arm is possible, which may be moved at a constant velocity on the surface to be polished. Dwell time for each tool is controlled using pulse width modulation (PWM), as required by the error map.

Taking advantage of the self-sustaining tool capacity (200) is also possible so as not having to use independent positioning systems for each of the tools (200) to ensure their parallelism on the work surface (300). Only one degree of freedom is required per tool (200) implemented by means of linear movement in the axis perpendicular to the surface, in conjunction with a force measuring device to guarantee polishing with zero force on the work surface (300) and being able to follow the local curvature or figure, as well as surface plane inclination.

Another advantage of this method is that the use of only one polisher feeding system for all the tools (200) is possible. This simplifies the system, increases efficiency and reduces costs.

Polishing process efficiency now becomes a function of the number of tools (200).

Simultaneous polishing with several tools (200) assigns to each tool (200) a surface section and borders between sections may be polished free of scars, either by means of the tessellation polishing method or by using pulse width modulation polishing. (PWM), as described above.

On the other side, there are several possible arrangements to accommodate multiple tools (200) for simultaneous polishing, such as, but not limited to, polishing in linear, matrix or spiral arrangements, which are described below:

Multi-Tool Polishing in Linear Arrangement

By assembling several deterministic polishing tools (200) on a polishing arm moved by means of a polishing robot (either a Cartesian CNC or robotic arm or any device for tool controlled movement), covering an area by moving the Arm in “X” and “Y” directions is possible. Each tool (200) is placed at a fixed distance δ from the other on the “X” axis. Sweep action on “X” axis is done by moving the arm a distance δ in this direction and advancing with the desired sweep pattern on the “Y” axis. The splice between polished sections for each tool (200) is handled by means of either tessellation or pulse width (PWM) polishing method, as described above.

There are some considerations that should be taken into account for this method, such as polishing the edges when polishing circular or non-rectangular surfaces. There will be times when at least one tool (200) is entering or leaving the surface to be polished, while others continue in polishing. Since this method takes advantage of the self-supporting ability of the tool (200) to conform the work surface (300), those tools (200) that approach the work surface edge (300) will lose buoyancy. These problems may be solved with an adequate path planning.

Multi-Tool Polishing in Matrix Arrangement

Linear arrangement may be expanded to any arrangement where multiple tools (200) are placed in a matrix array, mounted on a robotic device to sweep the surface to be polished. This allows maximizing the number of tools (200) and minimizing polishing time. The principle of operation is equal to the linear case, but adding m lines. This is equivalent to implementing m polishing runs in a single iteration, further increasing the efficiency of the polishing process.

Multi-Tool Polishing in Spiral Arrangement

An efficient polishing of a surface with axial symmetry is possible when positioning multiple tools (200) on a spiral arm, which in turn moves a distance δ on one of the Cartesian axes, just as in the linear arrangement method, so that each tool (200) covers the area assigned to it. The arm may be either moved around the symmetry axis of the surface to be polished, or rotate the surface on a turntable. Proposal and solving of a variational equation is possible for a parameterized spiral curve in such a way that “n” tools (200) are spaced apart equidistantly from each other over the entire length of this spiral curve, such that each tool (200) polishes the same amount of area. Extension of this methodology by adding more spiral arms to increase process efficiency is also possible.

Other Arrangements and Possibilities

In order to allow tool movement (200) the use of any computer controlled mechanism as a device allowing sweeping of said tool(s) (200) on the work surface (300) to be polished is possible, including but not limited to rotary tables, Cartesian CNC machines, articulated robots. Simultaneous polishing may be also performed with multiple tools (200) mounted on multiple robots.

A combination of any of above described methods or with the polishing method described for Mexican patent '048 tool is also possible each other, depending on the item and particular surface to be polished, to achieve the best possible solution for a polishing issue, optimizing polishing process efficiency and converging more quickly towards the intended surface. The present invention will be better understood from the following examples, which are presented solely for illustrative but not limitative purposes, in such a way as to allow a better understanding of the embodiments of the present invention, without implying that there are no other embodiments not illustrated that may be carried out based on the description above:

EXAMPLES
Example No. 1

A deterministic hydrodynamic tool prototype for pulsed polishing of optical surfaces was built, having coupled the mixer module of the present invention, where said tool had a 7 mm footprint and tested for linearity. FIG. 2 of accompanying drawings shows the results of erosion vs. dwell time. Pulse width varied in constant increments, from 10 ms to a maximum of 500 ms, because the tool moved incrementally by 0.2 mm, overlap was 35 times on each footprint diameter of said hydrodynamic tool. Erosion was measured using a Fizeau interferometer and the result was normalized, then removal corresponds to a single tool pass on each point along the line being polished. Error bars are basically due to errors produced by subtraction of the base reference during interferogram reduction. A removal resolution of 0.1 nm/ms may be noticed from data. Apparent polishing effects could be noticed from 25 ms. Such effect may be attributed to solenoid valve response time, where said response time may be improved by the use of faster actuators.

Arrangement modification of the mixer module allows controlling pulse duration with respect to a repeat frequency or pulse width modulation (PWM). For this end, repeat frequency must be kept within a tool footprint width diameter, which translates in time for a given tool velocity. In an extreme case, where duty cycle is changed between 0 and 1 while maintaining a constant velocity, creation of a discrete or pixelated pattern useful for determining the pulsed tool response function is possible. Said pattern is shown in FIG. 3 of the accompanying drawings, where a constant velocity of 2000 mm/min has been maintained and alternating the erosive process between turning the tool on and off at a 5 Hz frequency. A fringe pattern at the interface between the regions may be noted having a slope corresponding to tool footprint diameter, which is the size of the polishing limiting element (poxel). This polishing pattern was obtained by sweeping the tool orthogonally to the pattern observed in said FIG. 3.

Where only a small part of the surface needs to be polished, this region has to be managed with the hydrodynamic tool (patent '048) turned on leaving behind unwanted footprints, as well as inlet and outlet marks. This problem is solved by means of the pulsed abrasive effect carried out with the hydrodynamic tool coupled with the mixer module of the present invention. When an isolated region in need of additional polishing is identified, a constant width dampening band surrounding it is defined, as illustrated in FIG. 4 of the accompanying drawings. Assuming that a fringe pattern is defined, the region is approached by the hydrodynamic tool in full operation, with Y=0 until entering into the damping zone. Here, velocity starts slightly increased up to the necessary value within the region, while intended dwell time is controlled by means of PWM at the same time. Damping region width is determined by CNC acceleration and deceleration capabilities. Within the region to be corrected, a pulsed or continuous polishing may be used to maximize hydrodynamic tool efficiency.

When polishing large surfaces, hydrodynamic tool efficiency is limited due to its footprint small size and its volumetric removal velocity. However, said efficiency may be improved by simultaneously polishing the surface with a plurality of hydrodynamic tools having coupled the mixer module of the present invention. Said tools may be mounted on independent polishing robots, as illustrated in accompanying FIG. 5, where each robot attacks a certain section of the surface. This is one of many options or arrangements that may be provided by using simultaneously more than one hydrodynamic tool and carrying out the optical surface pulsed polishing.

Although reference has been made in previous description to some embodiments of the mixer module to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces, as well as to said pulsed polishing process, other embodiments that were not described in detail herein may be possibly developed based on above performed description. Therefore, it should be emphasized that numerous modifications to such certain embodiments are possible, but without departing from the true scope of the present invention, such as modifying the number and arrangement of the interrupter elements, polishing liquid, and many other modifications. Therefore, present invention should not be restricted except as established in the state of the art, as well as by the appended claims.