FIELD OF THE INVENTION

The present invention relates to techniques and principles used in Astronomy and high-precision Optics, as well as the development of tooling that allows carrying out a process that goes from corrective grinding to high precision polishing on surfaces requiring high optical quality, and more specifically, the invention relates to a mixer module for a deterministic hydrodynamic tool to accomplish 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.,SPIEVol. 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: it is only possible to polish high hardness materials; work surfaces are deformed by pressure exerted on them by tools requiring rigid supports for them; they tend to leave a fallen edge due to a 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 that do not have the advantages of a machine with several degrees of freedom as required, for example, for polishing an off-axis surface.

The problems of the methods disclosed above were overcome by using “stressed lap” type tools, consisting of tools that actively deform to polish spherical surfaces more easily. However, these 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 fine polishing of optical surfaces, namely: polishing by means of an ion beam (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 beam is described in U.S. Pat. Nos. 5,786,236 and 5,969,368, where said technology is based on the bombardment of the 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. The process is iterative, based on an error map of the work surface that is used to correct 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 an orthogonal beam incidence on the surface.

A 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 hand, fluid jet polishing (Booij, S. M., et al.,Optical Engineering, August2002, 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 developed, grinding the surface to be polished with an abrasive fluid beam. The jet is directed to the surface through a nozzle placed at a certain angle and distance from the work surface. This polishing method has limitations because the generated erosion footprint is very small and generates low removal rates. Surfaces that can be polished 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 by the same inventors of the present invention, 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 the work surface. Said tool was developed to solve problems that the available technology had not solved at such time, because in addition to the 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 was needed to achieve a high-precision finish on a surface.

The hydrodynamic tool of Mexican patent No. 251048 has no moving parts and is arranged by interchangeable modules, namely a mixer module that mixes two or more components of a polishing substance to form an abrasive foam that includes a porous cavity to control the density of said abrasive foam; a module of at least one rotational acceleration chambers that have an optimized hydrodynamic geometry, that minimizes random turbulence and creates a single, organized vortex that allows the mixture of air and abrasive fluid to be rotationally accelerated. These acceleration chambers include a set of power injectors in its periphery; an aerostatic suspension system, that generates a fluid layer over which the tool floats, 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, consisting of an abrasive foam, is produced, which, when leaving the hydrodynamic tool, radially and parallel to the work surface, expands onto the work surface creating abrasion in an annular, stable, uniform and repeatable footprint. This footprint, dependent upon the tool operational parameters, namely abrasive fluid supply flow, density and pressure, as well as pressurized air supply pressure, consists of a central low pressure zone, surrounded by a high pressure zone that cancel each other out, giving the tool a self supporting capacity or buoyancy. The hydrodynamic tool permits carrying out all the processes needed to obtain a very high-precision optical surface, from corrective grinding to fine polishing without the need of changing tools, avoiding friction against the work surface, wear and deformation of the tool, and also allowing 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 No. 251048 shows the limitation of not being able to interrupt its erosive action during the polishing process due to its internal hydrodynamic geometry. The operating parameters of the hydrodynamic tool, which consist of a controlled supply of pressurized air and polishing fluid into said tool, create the stability conditions that give the tool the ability to float over the surface to be polished, also called tool buoyancy or self supporting capacity, that also form the tool erosion footprint that produces erosion that removes material in a controlled manner. Interrupting any of these supplies will break up the stability conditions: the tool will cease to float over the work surface and the tool influence function will lose its erosive power. As mentioned above, interrupting the supply of the polishing solution causes the tool to lose its stability and buoyancy, requiring it to always be turned on, which forces requires having to sweep the entire surface which removes material in the process. This reduces the overall efficiency of the polishing process, as erosion will always be present, even in areas where polishing is not necessary, forcing higher than necessary process times, as well as excessive removal of material. This is disadvantageous for work on large surfaces, where polishing times can be tens of hours per run, and where polishing should not be interrupted in order to prevent the formation of splicing scars.

In order to solve the limitations of the hydrodynamic tool described above, a new mixer module is presented here that is coupled to the hydrodynamic tool from Mexican Patent No. 251048, and replaces the original mixer module of said patent, where the internal design of the mixer module in which the foaming step is carried out has been modified, so that the supply of polishing solution can be interrupted without losing the operational stability of the process, allowing polishing by “poxel” (Polishing Element) that, together with the hydrodynamic tool advantages possessed by Mexican Patent No. 251048, henceforth, the “hydrodynamic tool”, 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.

SUMMARY

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

The density of the abrasive foam depends on the pressure ratio with which air is injected into one inlet of the module, and the polishing fluid into the other inlet of the module. It is important to ensure that the abrasive foam dwell time is less than one millisecond within this mixing step.

In a further aspect of the present invention, a method for carrying out the deterministic polishing process is also described by using the deterministic hydrodynamic polishing tool having the mixer module of the present invention coupled to it, comprising the steps of: (a) generating an error map of the work surface to be polished from an interferogram; (b) parting from the error map, generating a dwell time map or 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 motion map for a polishing robot which allows to sweep the entire work surface to be swept in order 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, onto which the mixing module of the present invention is coupled, simultaneously mounted on a single machine or several independent machines and in different arrangements; and, (e) generating a new error map of the polished work surface, and as necessary, repeating steps (a) through (d) until the desired optical figure is obtained.

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

Likewise, the mixer module to be coupled to the deterministic hydrodynamic tool allows for several arrangements which accommodate multiple hydrodynamic 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 on one or more machines using the above cited arrangements and other arrangements.

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 with an internal geometry that minimizes random turbulence and allows pulsed polishing of optical surfaces, as said tool is provided with the ability to instantly interrupt the abrasive effect, but without losing the stability of the operational parameters and buoyancy of the hydrodynamic tool onto which the mixer module of the present invention is coupled and which are described in the background section.

Another object of the present invention is to provide the mixer module with the ability 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 the present invention is to provide the mixer module with the ability to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces. This allows carrying out said pulsed polishing by tessellation (or by sectors), since polishing paths can be spliced without leaving a footprint “scar”.

Still a further object of the present invention is to provide the mixer module with the ability 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 tessellation polishing that optimizes the splice path.

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

Even another object of the present invention is to provide the mixer module with the ability to be coupled to a deterministic hydrodynamic tool for pulsed polishing of optical surfaces that allows to 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, a velocity map is calculated from the error map of the surface to be polished to correct the surface and, parting from the error map, a time map with different pulse durations is calculated, so that the pulse duration determines the volume removed by each “poxel”.

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

The 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 the 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.

