The present invention relates generally to the need in many types of machines and devices to constrain motion along or about certain axes or directions while facilitating low friction guided motion along or about other axes or directions. The invention enables a new method for the construction of sliding joints which are able to accurately guide motion along a desired axis or direction while constraining motion and providing strength and support along other axes or directions. Due to its simplicity and low cost the invention relates to many types of machines and devices including milling machines, vices, and lathes.
There is a well-known need in the machine art for accurately guided motion. There are often significant forces involved in guiding or driving machine members so the means of constraining and guiding motion must be strong enough and rigid enough to withstand these forces.
In machine tools, for example in milling machines, ways are used to constrain motion in two directions and accurately guide and allow motion in a third direction. For example, the ways on the column of a vertical milling machine allow guided motion in the “z” direction (vertical movement) and constrain motion in the “x” and “y” directions (horizontal movement). The ways also constrain rotation about all three axes (x, y, and z). Referring to degrees of freedom (DOF) there are 6 possible DOF: 3 linear along the x, y and z axes and 3 rotational about the x, y and z axes. The ways on the column of a vertical milling machine constrain 5 DOF and leave 1 DOF unconstrained. This results in accurately guided motion on the unconstrained DOF, which is accurately guided linear movement along the z axis in this case.
In yet another example a rotating leadscrew sliding in a nut is used to drive a machine table along one axis. In this application it is extremely important that there is as little backlash, or clearance, between the mating components as possible to ensure accurate positioning. Internally threaded plastic nuts or more complicated ball nuts in combination with a leadscrew are often used in the prior art. Achieving accurate alignment while minimizing backlash and providing a low friction joint has previously required extremely accurately formed parts which make it difficult and costly.
There therefore exists a need for a low-cost construction that provides strength, stiffness, and accurate alignment of sliding and/or rotating parts in some directions while still allowing movement with low friction in a different direction. Various aspects of this need have been recognized in the prior art.
The prior art includes methods for providing threaded apertures in devices made by a molding process. U.S. Pat. No. 3,528,637 (Bedford) describes a method for molding internal threads in an aperture for receiving a threaded member. The method described in Bedford requires a die and core set which are used in a molding machine. Once the threaded part has been produced in a molding machine it is removed and then subsequently assembled into a device.
U.S. Pat. No. 4,079,475 (Thompson) describes a method of casting or molding a single internal thread in a product using an external mold and core pins. U.S. Pat. No. 4,554,962 (Wright) describes yet another method of molding or casting an internally screw threaded article using flat core members within the mold cavity. Here again a complicated molding machine with molds and core pins is required to produce internally threaded apertures.
The above methods disclosed in the prior art for forming internal threads from molded or cast parts all require molds, core pieces and the associated machinery to manipulate mold pieces and inject material. In order to achieve the close clearances between components necessary for accurately guided motion precise manufacturing tolerances are required on molds, core pieces and the associated machinery.
The need to provide accurate alignment between a driving member such as a leadscrew and a driven member such as a nut or ball nut is also well known in the prior art. U.S. Pat. No. 5,142,929 (Simpson) describes a ball nut with ball bearings used in conjunction with a leadscrew to provide accurate alignment and reduce backlash between the ball nut and lead screw. Ball nuts are complicated and expensive devices which are difficult to fabricate and assemble.
Another common need in machines and other devices is the need for accurate sliding linear alignment. U.S. Pat. No. 5,330,272 (Stoll) describes a linear drive using a longitudinal slot and a guide part which is guided for motion along the longitudinal slot. Again precise manufacturing tolerances are required on both the slot and guide part in order to accurately guide motion.
Yet another common need in machines and other devices is the need for accurate rotating alignment. U.S. Pat. No. 4,967,465 (Frank) describes a method of assembling a rotor retaining ring system to provide rotating alignment between the body and rotating member of an electric motor. The retaining rings require precise tolerances and require disassembly for replacement.
The need for accurate alignment in vices is also known in the art. U.S. Pat. No. 4,043,547 (Glomb) describes a machine vice with features for accurate aligning purposes. The vice components require precision machining and are expensive to manufacture with high accuracy.
The above methods disclosed in the prior art describe various methods that have been used to produce components which allow accurate alignment and positioning combined with guided motion.
Attaching polymers to threaded fasteners is also known in the art for the restriction of rotation to provide a locking torque. U.S. Pat. No. 3,784,435 (Bagheri) describes a method of forming a plastic patch on a screw fastener used to lock the fastener in place. This method is not applicable to forming internal threads which allow movement between a driving device such as a leadscrew and nut.
U.S. Pat. No. 4,706,352 (Furmanek) describes forming seats used to support bearing surfaces for slidable alignment by filling a pocket with a low friction epoxy material which hardens in place. The seats made of low friction epoxy material described by Furmanek are not bearing surfaces, but rather seats supporting bearing surfaces. Further, the method disclosed by Furmanek requires removable tooling blocks to form the bearing seats, and the seats are not formed by extrusion, simply by pouring a hardenable fluid into a cavity. Finally, in Furmanek as bearing surfaces wear they will need to be removed and replaced.
U.S. Pat. No. 5,592,728 (Susnjara) discloses a method of forming a guideway using a hardenable structural polymer. In Susnjara removable fixturing or tooling is required to position components prior to using the hardenable structural polymer and barriers are required to contain the hardenable structural polymer while it hardens. Once the hardenable structural polymer in Susnjara hardens it cannot be reformed in place. When the bearing surfaces in Susnjara are worn and need to be replaced the old structural polymer must first be removed. Then fixturing and tooling as well as barriers are required to re-create a new bearing surface.
U.S. Pat. No. 3,115,696 (Evans) discloses a method of manufacturing a slide unit that includes bonding a solid pad of thermoplastic material to one guide surface, heating one of the slide components, assembling the slide, and then cooling the slide components. Evans requires bonding of the thermoplastic material to one of the guide surfaces. Evans does not disclose completely liquefying the thermoplastic material so that it conforms to the shape of the joint between sliding components. Evans also does not disclose reforming of the thermoplastic material after the initial melting operation to recover from wear. There is no extrusion or even injection of liquid material disclosed by Evans.
In view of the foregoing disadvantages inherent in the design, manufacture, and assembly of sliding joints with guided motion in the prior art the present invention provides an improved design and method to simply and inexpensively build sliding joints with minimal clearance between the mating parts. The simplicity and low-cost of the design will be advantageous for many machines.
For many types of devices and machinery one part of the machine must be accurately positioned while it is moved through precise motion increments. The sliding motion must be accomplished in a smooth and efficient manner with a minimum amount of friction. In the past to provide the necessary stability and efficiency of operation precise machining operations were performed to form mating surfaces with minimal clearances between the sliding member and support members. These machining operations are quite expensive and time-consuming and are also subject to error.
In addition, in order make to maintain precise alignment the sliding bearing components were required to be periodically removed and replaced due to wear. This is expensive and time-consuming because it requires various portions of the machine or device to be disassembled. On some devices disassembly and replacement of bearing components is sufficiently expensive that the devices are discarded and not rebuilt once the bearing surfaces have worn.
In addition to requiring the costly purchase of new machines or devices discarding rather than repairing machines consumes energy and material resources. That is to say it is less sustainable to discard machines than to design them so they can be conveniently repaired and reconditioned.
Further, smooth and efficient operation of sliding members often requires low friction drag combined with vibration damping at the sliding connection. Materials with optimal low friction and vibration damping properties often wear faster than other materials so their use in many devices prior to the present invention was not economically feasible.
The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new and improved construction for sliding joints that provide guided motion which has all of the advantages of the prior art and none of the disadvantages.
To achieve this purpose the present invention essentially comprises a design and method of forming precise bearing surfaces in place that eliminates the need for expensive machining of sliding components and also provides for the ability to conveniently and inexpensively reform sliding bearing components in place without the need to disassemble machine components. The design can use materials that reduce friction and damp vibration in a machine.
The invention is a design and method of producing sliding components which include cavities into which a hardenable fluid is inserted after the sliding components have been assembled. The method of making a sliding joint includes the steps of fabricating opposing sliding surfaces with cavities between them and then introducing a hardenable fluid into these cavities. When the hardenable fluid hardens it forms bearing surfaces that conform precisely with essentially zero clearance between the hardened fluid and the opposing slide members. The design of the opposing sliding surfaces includes features that, when they are filled with the hardened fluid, serve to ensure the hardened fluid is properly located and supported.
The method also includes the ability to use hardenable fluids that can be re-liquefied in place, for example by melting, and allowed to re-harden. When used in this embodiment the method allows worn bearing surfaces to be completely reformed in place without the need for disassembly of the machine or device.
The invention enables many sliding elements of a machine tool or other device to be constructed of components with relatively relaxed tolerances and then assembled into a final sliding construction with minimal clearances between components. This allows for accurate positioning and support and minimal friction in the desired direction of travel. Many different constructions which require accurately guided sliding motion can be fabricated using the invention.
There has thus been broadly outlined the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter.
In this respect, before explaining the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description and illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways.
Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the design of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
It is therefore an object of the present invention to provide a new and improved design and method for producing guided sliding surfaces which enables machines and devices to be built with precise tolerances and lower manufacturing and assembly costs which has all of the advantages of prior art machines and none of the disadvantages.
It is another object of the present invention to provide sliding connections using a low friction material which are accurately located and have a long service life by virtue of the ability to easily reform the bearing material in place without the need for disassembly of a device.
These objects, together with other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the following detailed description. For a better understanding of the invention, its operating advantages, and specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive material in which there is illustrated a preferred embodiment of the invention.
Further, the purpose of the abstract of this invention is to enable the US Patent and Trademark Office, the public generally, and especially scientists, engineers and practitioners in the art not familiar with patent or legal terms or phraseology to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The abstract is not intended to be limiting as to the scope of the invention in any way.
The invention will be better understood when consideration is given to the following detailed description of the invention. Such description makes reference to the following drawings:
With reference now to the drawings, wherein like numerals designate like parts,
A wide range of materials can be used for reformable bearing material 36. Ultrahigh molecular weight polyethylene (UHMWPE, UHMW) is used in the preferred embodiment. Other versions of polyethylene can be used and different types of plastic or other materials can be used for the bearing material. Key features of the bearing material are low sliding friction, good mechanical strength, and the ability to flow when heated and solidify when cooled.
Leadscrew 10, nut 30, and cap 37 are typically formed of metals such as steel or aluminum in preferred embodiments of the invention. They can, however, be formed of plastic or any other material provided it has sufficient strength to withstand the required forces and remains stable at temperatures that are required to melt the reformable bearing material.
In the preferred embodiment of the invention the assembly shown in
Shoulders 44 formed by clearance hole 31 serve to support leadscrew 10 in its proper position during the extrusion process. Clearance between clearance hole 31 and nut 30 also provides a means for air to escape as the reformable bearing material is extruded into the cavities. Alternatively, the extrusion could be done in a vacuum.
Once the desired amount of reformable bearing material has been extruded the assembly shown in
The assembly shown in
By using leadscrew 10 as shown in
If it is desirable to constrain a shaft to linear motion shaft 20 as shown in
Finally, if it is desirable to locate a shaft without constraining either linear movement in an axial direction or rotation a plane shaft 26 as shown in
It should be noted that while round shafts have been used to indicate various embodiments of the invention the invention is not limited to shafts of round shape. Shafts with square, rectangular, or any other cross-sectional shape can be used in place of leadscrew 10 in
Another feature of the present invention is that in the preferred embodiment no additional tooling pieces are required to locate the sliding joint components. The sliding members themselves are designed to support each other before and during the extrusion process. This is shown in
Reformable bearing materials as used in the present invention will wear over time. After wear has occurred precise tolerances can be reestablished by reheating the assembly shown in
In many instances it will be desirable to be able to reform the sliding joint of the present invention without disassembling the sliding connection from a machine or device for heating. It is also desirable to be able to automatically reform the sliding joint using an electrical heating means 50 as shown in
In
It should be noted that various configurations of electrical heating means 50 can be used to heat sliding joints of different configurations. In addition other heating means such as using inductive heaters or applying heat locally to various portions of the sliding joint as required can be used to make bearing material 36 flowable.
In addition, a spring is only one possible compression means. Other possible compression means include air pressure, hydraulic pressure, gravity and an electrical solenoid.
This creates a sliding joint with essentially zero clearance that supports and locates the upper way with respect to the lower way while allowing slidable motion in one direction only. No adhesive material or other fixture is required to support bearing material 68 in the cavity formed between nested ways 60. The shape of the cavity itself constrains the bearing material 68 in this embodiment.
Rectangular nut 30 is attached to machine tool slide 75 which is supported on a bottom machine tool way 76. By rotating lead screw 10 with a driving means (not shown) force is transmitted to rectangular nut 30 and slide 75 is moved along way 76.
In the embodiment shown in
A key feature of the present invention is the ability to create precisely guided sliding surfaces without the need for highly accurate machining operations using a reformable bearing material. An additional key feature of the present invention is the ability to reform the bearing material in place to recover from wear without the need to disassemble machine components and to thereby recover accurately guided sliding motion.
Another important feature of the present invention is that no removable tooling is required for the formation of sliding joints. Hardenable bearing material can be extruded in place using the geometry of the opposing sliding surfaces to constrain the bearing material.
Yet another important feature of the present invention is that it enables a method of machine tool construction utilizing common elements and machining processes to create joints which accurately guide and drive machine members which greatly reduces the cost of a machine tool. This is especially advantageous for low-cost machine tools intended for the education or maker markets.
Yet another important feature of the present invention is that the cavities into which the reformable bearing material flows can be used to hold the reformable bearing material in place in such a way that no adhesive, additive or fixturing is typically required, although such adhesives, additives or fixturing could be used if desired.
The advantages of the invention should now be readily apparent to those skilled in the art without the necessity for a more detailed description of the elements. With respect to the above description it is to be understood that the optimal dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly, and use, are deemed readily apparent and obvious to one skilled in the art. All equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.
Therefore, the foregoing is to be considered as only illustrative of the principles of the invention. Since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
Number | Date | Country | |
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62371158 | Aug 2016 | US |