Bearings – Linear bearing – Fluid bearing
Reexamination Certificate
1999-06-30
2001-06-19
Marmor, Charles A (Department: 3681)
Bearings
Linear bearing
Fluid bearing
Reexamination Certificate
active
06247845
ABSTRACT:
DESCRIPTION
The present invention refers to a process for the manufacture of a base for pneumostatically supported sliding of mobile cars, in particular for measuring and/or automation equipment, and to a base obtained with said process.
Pneumostatic support technology is nowadays used in those fields requiring high mechanical stiffness, high precision in the translation movement and significant reduction of drag friction: therefore, typically in the high precision measurement and mechanical assembling systems, in the field of electrical components and where the noises of traditional mechanical equipment are not compatible with their housing environment, as in automation of Laboratory Medicine.
Currently, the technology consists in maintaining between two objects with great planarity and hardness and very low roughness a thin air cushion (depending on the characteristics of the system the opening can vary between 5 and 15 microns), that represents the sliding element between the two objects. Due to the extreme precision, machining and treatment of the sliding surfaces are particularly delicate.
In the tradition of the technology the base is made of honed hard stone (fine grain black granite) on which slippers made of quenched and ground stainless steel or of anodised “packed” aluminium “fly” (in the presence of air). As known, the anodising of aluminium causes the metal to get covered with a very hard epitaxic oxide (corundum hardness).
Granite, appreciated for its mechanical stiffness and its low coefficient of thermal expansion, has a serious limitations as to weight (as a function of the dimensions required to obtain the specified stiffness) and to fragility: when hit, it chips or even worse it fractures and it irreparably loses its functionality.
Another frequent reason for system degradation is due to the presence of impurities in the air used to support the mobile part (as for example condense water or oil), impurities that can obstruct the same holes for the adduction of air to the slippers and can cause their “landing” (that is the contact between the respectively mobile surfaces) with the inevitable irreversible damaging of the surfaces containing the air cushion. Whereas the slippers are easily replaceable, the same cannot be done with the machine base, which must undergo a heavy intervention for its replacement.
Due to the weight of the granite this has been obviated by the use of metallic structurals (as for example chromium steel or anodised packed aluminium) whose shape, without compromising the structure stiffness, is such as to contain the weight of the same structure within reasonable limits.
In addition, a higher thermal expansion coefficient is obtained, which is tolerated or compensated with mathematical calculations.
But an acceptable solution to the fragility and mechanical vulnerability of the base of metallic structural shapes has not been found: in fact, even if chromium steel and anodised aluminium are less agile than stone, they are nevertheless as much vulnerable to collisions with heavy and blunt objects or to the “landing” of surfaces bearing a heavy weight and not as much hard. What stays underneath the hard material, in fact, does not represent a barrier against the possible denting of the base due to the aforementioned accidents.
Therefore the present technology of pneumostaticsupport, in view of the several advantages, bears the disadvantage of being costly and highly risky and, therefore, it is not very widespread: in particular the aspect of its risk is prejudicial to a wide employment since the damage to the sliding planes due to collisions or to the fall of heavy objects irreparably ruins the apparatus and requires the replacement of the machine base. This operation reveals being costly in terms of the intrinsic value of the piece to be replaced as well as of the inevitably very long technical time.
The object of the present invention is to implement a process capable of enabling the manufacture of a base that can be repaired in an easy manner and at low cost, in case of an accident prejudicing the well functioning of the base itself.
According to the present invention, such object has been attained by means of a process, characterised in that it involves the employment of a metallic support provided with channels for housing respective sliding tracks for pneumostatically supported slippers and the realization of each one of said tracks by application of a layer of resin on the bottom of a respective channel and subsequent mechanical machining of the same until the required characteristics of planarity and parallelism are obtained.
The idea that was at the basis of the present invention and that allowed to overcome the limitations of the known technique consists in the fact of having abandoned the conviction that the characteristic of hardness of the supporting material was absolutely essential: such characteristic, even if it bears some advantages, is not absolutely necessary to the proper functioning of a pneumostatically supported equipment. What it is necessary to guarantee is a great homogeneity of the material, a low porosity (compactness of the matrix) and its perfect machineability in such a way so as to consent the creation of a surface tat, when coupled with the sliding slipper, makes available an air cushion for the support of the mobile equipment which remains steady through time and space.
From this simple consideration, that is from the fact to consider as unessential the hardness of the support, comes the solution to the aforementioned problem. It is in fact quite evident that there are applications for which granite remains irreplaceable and one therefore accepts the limitation imposed by the material in view of its specific performance; but it is also true that in most of the aforementioned applications a traditional base offers more disadvantages than advantages.
The present inventions deals with these applications. Starting from the presupposition that the hardness of the support is not a fundamental requirement, the attention has been focused on those materials and on those processes having the following characteristics:
a. repairability of the surface (re-establishment of the conditions of suitability to the use after an accident that has altered the characteristics of the surface itself);
b. low porosity (matrix compactness);
c. perfect machineability;
d. mechanical isomorphism.
This has lead to two different embodiments of the process according to the invention.
A first embodiment provides that on the bottom of the channels of the metallic support an accentuated roughness is preliminarily produced (what is obtained sparing the elimination of the tracks produced by the mechanical roughing) and that a resin is poured on the surface thus roughed that is subsequently hardened and machined until the required characteristics of planarity and parallelism are obtained.
The hardening process can be done either at ambient temperature or in an oven and, depending on the particular resin being chosen, it could be necessary to perform the first part of the process in a vacuum chamber so as to facilitate the release of the gases entrapped in the resin during the mixing phase.
As for what concerns the type of resin, the attention has been drawn on the plastic resin that can be poured in a mechanically predisposed seating in order to guarantee an adequate mechanical as well as chemical gripping.
Such resins must also have the characteristics of being capable to be “charged” by means of powder-like components aimed at conferring particular chemical-physical-mechanical characteristics to the finished product or to contribute to increase particular characteristics already possessed by the resins themselves.
The families of resins suitable to the purpose are those of the acrylic, epoxidic; polyester and polyurethane high density resins.
As an alternative, a second form of embodiment of the process according to the invention provides that the application of the resin layer is done by gluing a strip of resin that is produced by industria
Berri Michele
Pedrazzini Gianandrea
Inpeco s.r.l.
Jacobson & Holman PLLC
Marmor Charles A
Parekh Ankur
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