Abstract:
A vacuum cup is made from rubber to resist damage and providing a vacuum seal without a separate gasket or O-ring. The vacuum cup may be one of several configurations suitable for different CNC machines and includes a rubber body comprising a bottom surface for mounting, a top surface including a vacuum area for holding a work piece, and a raised edge around the perimeter of the top surface for sealing against the work piece. The bottom surface may have any one of a variety of machine interfaces to cooperate with various machines. A vacuum passage connects the bottom surface with the vacuum area and a check valve may reside in the vacuum passage. The rubber body is sufficiently strong to resist flexing due to vacuum or work piece weight and the vacuum area includes work piece supports for contacting a work piece held on the vacuum cup.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to vacuum hold downs and in particular to vacuum cups for CNC machines. 
   Various machines exist for performing operations on various types of materials. Vacuum is often used to hold the material in place while the operations are performed. Examples of such machines are Biesse machines made for boring and routing of engineered (for example, particle board) and solid wood, composited, plastics, and soft metals (for example, aluminum). These, and other machines, often utilize vacuum pods or cups which may be positioned for a particular work piece or operation. The cups may interface with the machine in various manners, and are generally approximately square and approximately six inches across, although the size and shape may vary. 
   Known cups are made from a phenolic material. Phenolic material is generally a plastic-like resin which is both hard and strong. Phenolic material is commonly used in as a wood worked surface, for example, as an insert for router tables, because cutters can cut into the phenolic material without damaging the cutter. Vacuum cups generally have narrow edges outlining the perimeter of a top surface of the cups for providing a vacuum seal, and cups made from the phenolic material are easily damaged when a cutter meets the narrow edges or when material is loaded onto the machine. The edges may be cracked, or a portion of the edge may break away. Unfortunately, even a small crack or chip is likely to spoil the cup&#39;s ability to maintain vacuum and prevent further use. The Phenolic (or similar hard material) also require a gasket to form a vacuum seal and material may slip on the hard surface. Such gaskets are often expensive and may easily be damaged. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention addresses the above and other needs by providing a vacuum cup made from rubber to resist damage and providing a vacuum seal without a separate gasket or O-ring. The vacuum cup may be one of several configurations suitable for different CNC machines and includes a rubber body comprising a bottom surface for mounting, a top surface including a vacuum area for holding a work piece, and a raised edge around the perimeter of the top surface for sealing against the work piece. The bottom surface may have any one of a variety of machine interfaces to cooperate with various machines. A vacuum passage connects the bottom surface with the vacuum area and a check valve may reside in the vacuum passage. The vacuum area further includes recessed work piece supports for contacting a work piece held on the vacuum cup when vacuum applied to the cup cause the raised edge to compress. The rubber material also reduces work piece slipping and allows higher feed speeds. In some cases, the rubber body is sufficiently strong to resist flexing due to vacuum or work piece weight and in other cases a strengthening insert, for example a Delrin® insert, is required to prevent flexing. 
   In accordance with one aspect of the invention, there is provided a vacuum cup comprising a substantially solid rubber body having a bottom surface, a top surface, and sides. A vacuum area is formed on the top surface and a vacuum passage passes between the bottom surface and the vacuum area. A raised edge resides around the top surface of the body for forming a seal with a work piece. Mounting features reside on the bottom surface for mounting the vacuum cup on a machine. 
   In accordance with another aspect of the invention, there is provided a vacuum cup comprising a substantially solid rubber body having a bottom surface, a top surface, and sides. A vacuum area is formed on the top surface and work piece supports reside in the vacuum area. A vacuum passage passes between the bottom surface and the vacuum area and a raised edge resides around a perimeter of the top surface of the body for forming a seal with a work piece. The raised edge is approximately 0.2 mm above the work piece supports. Mounting features are molded onto the bottom surface for positioning the vacuum cup on a machine. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
       FIG. 1A  is a top perspective view of a first embodiment of a vacuum cup according to the present invention. 
       FIG. 1B  is a bottom perspective view of the first embodiment of the vacuum cup according to the present invention. 
       FIG. 2  is a bottom perspective view of a second embodiment of the vacuum cup according to the present invention. 
       FIG. 3  is a bottom perspective view of a third embodiment of the vacuum cup according to the present invention. 
       FIG. 4A  is a top perspective view of a fourth embodiment of the vacuum cup according to the present invention. 
       FIG. 4B  is a bottom perspective view of the fourth embodiment of the vacuum cup according to the present invention. 
       FIG. 5A  is a top view of the second embodiment of the vacuum cup. 
       FIG. 5B  is a bottom view of the second embodiment of the vacuum cup. 
       FIG. 5C  is an end view of the second embodiment of the vacuum cup. 
       FIG. 6A  is a cross-sectional view of the second embodiment of the vacuum cup taken along line  6 A- 6 A of  FIG. 5A . 
       FIG. 6B  is a cross-sectional view of the second embodiment of the vacuum cup taken along line  6 B- 6 B of  FIG. 5A . 
       FIG. 7A  is a top perspective view of a fifth embodiment of the vacuum cup according to the present invention. 
       FIG. 7B  is a bottom perspective view of the fifth embodiment of the vacuum cup according to the present invention. 
       FIG. 8  is a cross-sectional view of the fifth embodiment of the vacuum cup taken along like  8 - 8  of  FIG. 7A . 
       FIG. 9  is an insert molded into a vacuum cup to reduce or prevent bending which may cause vacuum leaks. 
   

   Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
   A top perspective view of a first embodiment of a vacuum cup  10   a  according to the present invention is shown in  FIG. 1A , and a bottom perspective view of the first embodiment of the vacuum cup  10   a  is shown in  FIG. 1B . The top of the vacuum cup  10   a  includes a raised edge  12  for sealing with a work piece supported and held by the vacuum cup  10   a , and raised work piece supports  14  for supporting the work piece. The work piece supports  14  preferably comprise a group of parallel bars and reside on support bases  16 . A vacuum passage  18  passes through the vacuum cup  10   a  and connects to a vacuum source. The interior of the raised edge  12  defines a vacuum area for creating a hold down force for holding the work piece. 
   The bottom of the vacuum cup  10   a  includes a machine interface  20  for cooperating with known CNC machines, for example a Biesse Rover 22 CNC Machining Center or a Biesse Rover 24 CNC Machining Center. The machine interface  20  is a cylindrical protrusion and includes indexing features (or fingers)  22  for cooperation with indexing grooves in CNC machines, and centering pads  24  for cooperation with a corresponding opening in the CNC machines. The vacuum passage  18  is shown extending through the bottom of the vacuum cup  10   a , and is partially blocked to provide a stop of a known check valve commonly used with vacuum cups. 
   Known vacuum cup are manufactured from a phenolic material. Phenolic material is generally a plastic-like resin which is both hard and strong. Unfortunately, such known cups break easily and must be replaced frequently. If a replacement is not available when needed, an expensive machine may be sit idle until a new part is obtained. The vacuum cup  10   a  according to the present invention is molded from substantially solid rubber and is much less susceptible to breaking. The vacuum cup according to the present invention is approximately one inch thick and preferably has a Shore hardness of approximately 80 Shore A. An example of a suitable material is compound number EXP7654-80B provided by R&amp;S Processing in Paramount, Calif. Compound Number EXP7654-80B is a natural rubber and is non-blooming. Blooming refers to a tendency of some compounds to give off a powder like material. Such powder reduced friction and would reduce the holding power of the vacuum cups. The compound is crosshatched during molding to equalize shrinkage across the part. Such crosshatching is important to maintain close dimensional tolerances. 
   Because the material used by the present invention is not stiff like the phenolic material used in known vacuum cups, the vacuum cups  10   a  may flex when vacuum is applied. Such flexing often affects the seal between the material and the vacuum cup. As a result, a vacuum cup according to the present invention often requires additional support structure to prevent flexing. In the instance of the cup  10   a , the additional support structure is a support ring  21  is added to the bottom of the cup. Such support ring  21  rests against a solid surface and thereby provides a support structure. 
   A bottom perspective view of a second embodiment of the vacuum cup  10   b  according to the present invention is shown in  FIG. 2 , and a bottom perspective view of a third embodiment of the vacuum cup  10   c  according to the present invention is shown in  FIG. 3 . The vacuum cups  10   b  and  10   c  include alignment features  26   a  and  26   b  respectively. The alignment feature  26   a  is rounded or a bullnose shape, and the alignment feature  26   b  is rectangular. The alignment features  26   a  and  26   b  are suitable for use with know CNC machines, and are configured to cooperate with grooves in a flat table machine to position the vacuum cup on the flat table machine. 
   A top perspective view of a fourth embodiment of the vacuum cup  10   d  according to the present invention is shown in  FIG. 4A , and a bottom perspective view of the fourth embodiment of the vacuum cup  10   d  is shown in  FIG. 4B . The vacuum cup  10   d  is similar to the vacuum cups  10   a ,  10   b , and  10   c , but includes side pads  28  along one edge of the vacuum cup bottom to cooperate with support rails of a machines. Such cup is used on machines such as a Biesse Rover 20 machine. The vacuum cup  10   d  further includes four fastener passages  30  for securing the cup to the machine. 
   A top view of the second embodiment of the vacuum cup  10   b  is shown in  FIG. 5A , a bottom view of the second embodiment of the vacuum cup  10   b  is shown in  FIG. 5B , and an end view of the second embodiment of the vacuum cup  10   b  is shown in  FIG. 5C . A cross-sectional view of the second embodiment of the vacuum cup  10   b  taken along line  6 A- 6 A of  FIG. 5A  is shown in  FIG. 6A , and a cross-sectional view of the second embodiment of the vacuum cup  10   b  taken along line  6 B- 6 B of  FIG. 5A  is shown in  FIG. 6B . The raised edge  12  rises approximately 0.2 mm above the work piece supports  14 . 
   A top perspective view of a fifth embodiment of the vacuum cup  10   e  according to the present invention is shown in  FIG. 7A , a bottom perspective view of the fifth embodiment of the vacuum cup  10   e  is shown in  FIG. 7B , and a cross-sectional view of the fifth embodiment of the vacuum cup  10   e  taken along line  8 - 8  of  FIG. 7A  is shown in  FIG. 8 . The vacuum cup  10   e  is similar to the vacuum cups  10   a ,  10   b ,  10   c  and  10   d , but includes recesses  34 , a “V” shaped vacuum slot  19 , and a support structure comprises an insert  32 . The insert  32  is a plate embedding in the vacuum cup  10   e  and is preferably a nylon insert, and more preferably a Delrin® insert, and is preferably approximately ⅜ inches thick. The insert  32  is preferably etched to provide better adhesion of the rubber vacuum cup body to the insert  32 , and more preferably the insert  32  is etched using plasma surface modification. 
   An example of a suitable plasma surface modification of the insert  32  is performed using a 2051 Series Plasma System made by TriStar Plastics, Corp. In Brea, Calif. Plasma is a state-of-matter which is different from the other three states (solid, liquid, or gas). In a steady state condition, plasma is a quasineutral cloud which contains free electrons and ions. In a disassociated state, plasma consists of electrons, ions, unexcited molecules and free radicals. Plasma may be generated by turning non-reactive molecules into reactive molecules by introducing energy, such as an electrical charge. Extremely reactive plasmas may be created by using an electrical charge to break up safe inert gases, for example, freons. When freons are electrified, they produce large quantities of chlorine and fluorine, both highly reactive compounds. These are the compounds which contain the ions and free radicals which actually do the “etching”. In addition, the directionality and degree of reactivity can be controlled by the amount of applied power. The ability to control the directionality and degree of reactivity of the plasma etching process enables the engineer to “control the etch”, which makes dry etching (e.g., plasma etching) more controllable than wet etching. 
   Methods for selecting parameters for plasma etching are well known to those skilled in the art. For plasma etching of the insert  32 , the plasma pressure is preferably maintained between 0.05 Torr to 2.0 Torr, and more preferably between 0.250 Torr and 0.350 Torr. The RF power setting is preferably between 20 Watts to 2500 Watts, and more preferably between 800 Watts and 1,000 Watts. The RF generator frequency is variable, but is preferably approximately 13.56 MHz. The gas species used in this invention may be any pure gas or gas mixture which would provide an oxidized surface. Commonly preferred gasses include oxygen (O2), nitrous (N2O), argon (Ar), helium (He), carbon dioxide (C2O), or any mixture there of. The duration of the treatment is variable based on polymer load (i.e., the quantity of polymer parts in the chamber to be treated) and surface area of the polymer load. Based on standard polymer load, and size of substrate the time is preferably between 2 to 45 min, and more preferably, the time is between 15 minutes to 25 minutes. Those skilled in the art would generally modify the time for their specific machine setup. 
   After a substrate has been treated using the above method, the surface is molecularly etched and chemically modified. This type of surface activation can be measured via goniometry (contact angle measurement) or dynes inks. 
   The governing equation is Young&#39;s equation where:
 
 Ysv−Ysl=Ylv *Cos Θ
 
where Ysv is the surface free energy of the solid in contact with vapor, Ysl is the surface free energy of the solid covered with liquid, Ylv is the surface free energy of the liquid-vapor, and interface Θ is the contact angle.
 
   Contact angles are measured in degrees. “Low” is below about 20° and “high” as 90° or above. Water on poly-tetrafluoroethylene PTFE is about 112°, very high. Low angles mean wettable. Surface energy (the terminology generally used for solids) and surface tension (the terminology generally used for fliuds) are measured in dynes/cm. Water has a surface tension of 72.8 dynes/cm at room temperature. The surface energy of most solids falls between 15 and 100 dynes/cm. If the surface tension of the fluid is below the surface energy of the solid, the fluid will spread rather than staying in a little droplet. Polymer surfaces are often treated to improve this wettability by raising their surface energy. 
   A detailed top perspective view of the insert  32  is shown in  FIG. 9 . The insert  32  is preferably made or pre-drilled with passages  30   a  aligned with the fastener passages  30  and passages  18   a  aligned with the vacuum passages  18  in the vacuum cup to simplify molding the vacuum cup  10   e . The fastener passages  30   a  and the vacuum passages  18   a  are preferably over-sized to allow inside edges of the fastener passages  30   a  and the vacuum passages  18   a  to be embedded within the vacuum cup. The outside dimensions of the insert  32  are undersized compared to the vacuum cup to allow embedding of the insert  32  within the vacuum cup. Additional holes  18   b  (one of a multiplicity of holes  18   b  is labeled in  FIG. 9 ) are spaced apart on the insert  32  to allow molding material to flow through the insert  32  to prevent the vacuum cup from ballooning when vacuum is applied thereto. A second “V” shaped vacuum slot  19   a  may be provided in the insert  32 , for example, to distribute vacuum and several of the holes  18   b  may be aligned with the slot  19   a  to help distribute vacuum. 
   While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.