Abstract:
This invention relates to a vacuum holder for securing workpieces, such as flexible media or printed circuit boards, through a suction force. Pressure responsive, one way flow valves are incorporated between chambers under suction openings to control the application of suction. This results in a restraining force that is uniform in time and space, resulting in a vacuum holder that has reduced pumping requirements.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to vacuum surfaces, such as drums, plates, or surfaces of other configurations, which use suction to secure a workpiece or flexible media positioned over suction openings located on the vacuum surface, and more particularly to configurations that allow the vacuum surface to respond to the shape and placement of the workpiece by providing suction only suction openings under or near the workpiece to the vacuum. The invention further relates to the use of vacuum surfaces used to secure printed circuit boards during the manufacturing thereof. 
     BACKGROUND 
     Vacuum tables, vacuum plates and vacuum drums, collectively referred to herein as “vacuum holders,” are workpiece holding and restraining devices having a vacuum surface. A common approach for manufacturing such a vacuum holder is to have many suction openings terminating at a vacuum surface. The application of a vacuum produces a pressure difference across the workpiece, which it turn imparts a suction force on the workpiece towards the vacuum surface. The position, size and shape of the suction openings relative to the workpiece determine the required amount of vacuum and the suction force per workpiece area. 
     The uses for vacuum holders include a variety of industrial and commercial applications that require locating, restraining or transporting pieces. For vacuum plates and tables, workpieces are commonly positioned on the plate and the suction force is then engaged. Vacuum plates are used, for example, to transport a printed circuit board (PCB) from a stack to a direct imaging exposure device such as the exposure device described in co-assigned U.S. patent application Ser. No. 60/107,842. Vacuum drums are commonly configured as rotating cylindrical surfaces and are used for transporting flexible media, such as film and paper. Vacuum holders are used to position, secure and transport paper or film for scanning or printing/exposing. Paper processing and printing machines, for example, use vacuum holders to transport film or paper from one part of the machine to another. Other machines, such as imagesetters, laser printers and rotary data scanning and recording devices, use vacuum drums to support flexible media during exposure or scanning. In these devices the drum rotates with the suction engaged. Suction attaches the media to the drum at the point of first contact with open suction openings, and then pulls the media around the drum as it rotates. 
     All vacuum holders with vacuum surfaces incorporate a series of channels and suction openings in the vacuum plate or drum, allowing for one or a few vacuum connections to provide suction over an area of the surface. In many early and some contemporary prior art systems, the internal vacuum plumbing is configured so that suction is applied to all suction openings simultaneously. Another approach for manufacturing vacuum holders is to use a “porous” surface instead of suction openings. Regardless of the approach taken, there is a balance between the flow restriction of the surface and the vacuum source. A large suction force over a large area usually requires a low restricted porous material with a high capacity vacuum source. 
     There are several problems inherent in prior art configurations that result in a vacuum pumping requirement larger than the minimum needed to secure the workpiece. Consider the operation of a vacuum plate in which the workpiece is placed on the surface, covering some of the suction openings. Uncovered suction openings have a constant pumping requirement, and thus there will always be an excess capacity whose amount is determined by the minimum workpiece size. Covered suction openings will have a large pumping requirement until a vacuum seal between the workpiece and surface is formed, at which time the pumping requirement diminishes, theoretically approaching zero for a perfect vacuum seal. The pumping requirement will decreased from an initial value which must accommodate all of the covered suction openings, to nearly zero as a vacuum seal is formed. Thus it is seen that prior art vacuum holders require vacuum pumps that are oversized relative to the minimum capacity needed to restrain the workpiece. 
     Similar problems also occur in vacuum drum applications. The drum first makes contact with and picks up the leading edge of a flexible media. As the drum rotates, the media wraps about the dram and is held in place at the point of contact with the drum. In this application, the number of uncovered suction openings, and hence the pumping requirement, decreases as the rotation proceeds and suction openings are covered. The vacuum system must be capable of accommodating all of the initially uncovered suction openings. 
     Having several suction openings not covered by the workpiece may also produce undesirable noise and vibration. 
     Thus the application of suction simultaneously to all of suction openings on the vacuum surface produces several problems in earlier prior art systems. These can be characterized as requiring vacuum pumping overcapacity due to 1) uncovered suction openings, and 2) exposing all covered suction openings simultaneously. The problems due to uncovered suction openings has been previously acknowledged but only partially addressed in several U.S. Patents. Thus in U.S. Pat. No. 5,716,048, Morrisette describes a drum mask placed over the drum, where the mask is configured to cover those suction openings not covered by the media. This solution effectively tailors the vacuum drum to a media size as determined by the available masks. As noted in Morrisette, a mask must be produced for every media size, and the operator or machinery involved must adapt to changes in media size by changing masks. While that invention improves the performance by lowering the pumping requirement for each media size due to changes in the number of covered suction openings, this prior art invention requires intervention by either the operator or some machinery to choose the appropriate mask size. Furthermore, the suction force may be different for different masks because the area kept uncovered and number of free suction openings may differ. 
     Both U.S. Pat. Nos. 5,183,252 and 4,202,542 describe various methods for allowing vacuum drums to accommodate a few different media sizes through valving mechanisms that applying vacuum to pre-selected patterns of suction openings. These solutions do not require the additional mask hardware required by Morrisette, but do require complex, externally switchable vacuum plumbing if many different media sizes are to be accommodated. As with Morrisette, these references must also incorporate means to detect the size or orientation of the media. Each of these prior art solutions adapts the vacuum drum to a predetermined number of media sizes and orientations, and thus is not easily adaptable to sizes, shapes or orientations not considered in the initial machine design. In addition, none of the prior art addresses the excess pumping requirement due to applying suction to all of the suction openings simultaneously. 
     U.S. Pat. No. 5,374,021 to Kleinman includes a vacuum chamber which is divided into several sub-chambers each connected via a control passageway to one or more suction openings on a vacuum surface. Each control passageway includes a valve which is biased to keep the passageway open, and configured to close when the sub-chambers openings are not covered by a workpiece and a vacuum is applied to the vacuum sub-chambers. The valves of the passageways to openings that are covered by a workpiece remain open so that a vacuum is applied to hold the workpiece. The Kleinman system thus in effect provides a “self adapting mask” comprised of all the valves that are of the passageways to openings that are not covered by the workpiece. This offers advantages over the Morrisette and systems of U.S. Pat. Nos. 5,183,252 and 4,202,542 in that the Kleinman system adapts to all sizes, shapes or orientations. 
     The Kleinman system, however, still has several shortcomings. In addition, none of the prior art addresses the excess pumping requirement due to applying suction to all of the suction openings simultaneously. 
     This aspect of the present invention provides the benefit of limiting stresses on fragile workpieces. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is providing a vacuum holder to restrain a workpiece with minimum or close to minimum vacuum pumping requirement. 
     Another feature of the present invention is providing a vacuum holder that can automatically adapt to a large number of workpiece sizes and orientations, using the same minimum or close to minimum vacuum pump requirement. 
     Yet another feature of the present invention is providing a vacuum holder that provides suction primarily to those suction openings covered by a workpiece. 
     Yet another feature of the present invention is providing a vacuum holder that can operate with a nearly constant, unregulated vacuum pumping requirement, independent of the workpiece size. Yet another feature of the present invention is providing a vacuum holder that is less bulky and less expensive as a result of decreased vacuum pumping requirements. 
     Yet another feature of the present invention is providing an adaptable vacuum holder that is both inexpensive and easily assembled. 
     Another feature of the present invention is the ability to reduce the stress and deformation of the workpiece through the slow, directional application of vacuum to the workpiece surface. 
     Another feature of the present invention is that it provides for holding media of different sizes with the same initial suction condition. 
     These and other features are provided for in an automatically adapting vacuum holder for supporting a workpiece through the application of a vacuum from a vacuum source, this vacuum holder comprising (a) a base having a workpiece support surface adapted for supporting a workpiece thereon, and (b) a vacuum plumbing system connected to the vacuum source through at least one vacuum port. The plumbing system includes (i) a plurality of chambers positioned along one or more directed lines of connection emanating from the vacuum port, each line of connection including a chamber directly coupled to one or more associated vacuum ports, (ii) a plurality of passageways positioned between any two chambers along any line of connection for controllably connecting each chamber along a line of connection to the next chamber further from the vacuum source along the line of connection, each passageway having a connected state and a disconnected state substantially connecting and substantially not connecting, respectively, the two chambers on either side thereof, and (iii) a plurality of vacuum bores each extending from the surface to a chamber to define a suction opening on the surface and configured to be substantially covered when a workpiece is placed thereon. Each chamber is either directly connected to the vacuum source or capable of being connected to the vacuum source via the passageways along a line of connection from the vacuum source. Each of the passageways from any particular chamber to the next chamber along any of the particular chamber&#39;s lines of connection is biased to be in the disconnected state to the next chamber along any of the particular chamber&#39;s lines of connection when the vacuum is not applied. Each of the passageways also is configured to remain in the disconnected state to the next chamber along any of the particular chamber&#39;s lines of connection if the suction opening of the vacuum bore of the particular chamber is not covered by the workpiece. Each of the passageways also is configured to be in the connect state to the next chamber along any of the particular chamber&#39;s lines of connection when the vacuum is applied and when the workpiece is placed on the surface so that the workpiece substantially covers the suction opening of the particular chamber and all the suction openings of the chambers closer to the vacuum source along any of the particular chamber&#39;s line of connection. In this way, the vacuum holder supports the workpiece and limits the number of uncovered suction openings to which the vacuum source is coupled by sequentially opening suction openings along the lines of communication, thus automatically regulating the amount of vacuum necessary to restrain the workpiece. 
     Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a cross-sectional schematic of the operation of an adaptable vacuum holder; 
     FIGS. 1B-1E are a series of cross-sectional schematics showing the operation of an adaptable vacuum holder with a workpiece in place; 
     FIG. 2A is a top schematic view of the lines of connection for an embodiment with a rectangular layout of multiple independent rows; 
     FIG. 2B is a top schematic view of the lines of connection for an embodiment with a rectangular layout of multiply interconnected rows; 
     FIG. 2C is a top schematic view of the lines of connection for an embodiment with a rectangular layout of diagonally interconnected rows; 
     FIG. 2D is a top schematic view of the lines of connection for an embodiment with a circular layout of multiply interconnected radial rows; 
     FIG. 2E is a top schematic view of the lines of connection for an embodiment with a circular layout multiple suction openings per connection; 
     FIG. 3A is a cross-sectional view of the preferred embodiment; 
     FIG. 3B is a cross-sectional view of the preferred embodiment with a workpiece; 
     FIG. 4 is a top detailed view of the gasket of the preferred embodiment; 
     FIG. 5A is a longitudinal sectional view of a prior art vacuum table; and 
     FIG. 5B is a fragmentary, exploded view of the vacuum table of FIG.  5 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Preferred Embodiment of the Adaptable Vacuum Holder Concept 
     A schematic illustration of the construction and operation of the present invention is shown in FIG.  1 . An adaptable vacuum surface  101  comprises a workpiece support surface  103  which may be a planar or cylindrical surface, or in general any surface capable of supporting a workpiece  133  (shown in FIGS. 1B-1E) through a suction force at a plurality of suction openings  105  to  109  located on surface  103 . A plumbing system  113  is capable of communicating vacuum from a conventional vacuum source  135  attached via a vacuum tube  137  and vacuum port  111  to suction openings  105  to  109 . Plumbing system  113  comprises a series chambers  114  to  118  with interconnecting channels  119  to  122 , flow valves  123  to  126  between adjacent chambers, and vacuum bores  127  to  131  connecting each chamber  114  to  118  to workpiece support surface  103 . The valves can be either in a closed state, shown schematically by valves  123  to  126  in FIG. 1A, or in an open state, shown schematically by valves  123  to  125  in FIG.  1 E. Thus each interconnecting channel and valve combination forms a passageway between chambers that can be controlled to be connecting or not connecting adjacent chambers along a line of connection. Closed valves prohibit the flow of ambient air external into vacuum surface  101  towards the vacuum source. Open valves that are adjacent to port  111  or form an unbroken chain of open valves leading to port  111  will draw ambient air into the vacuum system, providing suction at the appropriately associated suction openings. The application of suction is thus limited to a sequence of openings connected through open valves to the vacuum source. 
     Note that while FIG. 1 shows each chamber connected via a single vacuum bore to form a single suction opening, alternate embodiments may include a set more than one bores extending from each chamber to the surface  103  to define a set of more than one openings for each chamber. The embodiments described herein are all shown and described with one suction openings per chamber, and how to extend to having several suctions openings from each chamber would be straightforward to those in the art. 
     Adaptive Operation of the Present Invention 
     The active response of the present invention to the application of vacuum will now be considered in reference to FIGS. 1B-1E. As depicted in FIG. 1A, valves  123  to  126  are configured to be in a normally closed state in response to small pressure differences across each valve. Prior to the application of a vacuum at port  111 , for example using vacuum source  135  connected to port  111  via vacuum tube  137 , the pressure in each chamber, and hence on either side of each valve, is equal to the ambient pressure external to mechanism  101 . The application of vacuum at port  111  results in an evacuation of chamber  114 . FIG. 1A shows the response of vacuum support  101  in the case where there is no workpiece on surface  103 . In this case suction opening  105  is unobstructed, and ambient air flows through suction opening  105  and bore  127  into chamber  114 , and finally through port  111 . As a result of pressure variations through plumbing system  113 , the pressure in chamber  114  will be slightly less than ambient, as determined by the characteristics of bore  127  and suction opening  105 . Valve  123  is configured to remain in a closed state by not opening in response to the slightly depressed pressure in chamber  114 . Suction will be applied at suction opening  105  but not to any other suction openings, since valve  123  prevents communication of vacuum to the rest of plumbing system  113 . Thus the response to the present invention to the application of vacuum without a workpiece is to restrict suction to suction opening  105  closest to port  111 . 
     FIGS. 1B-E illustrate the operation of the present invention, with increasing time, to the application of vacuum to port  111 . FIG. 1B is at a time prior to and just subsequent to the application of vacuum, FIGS. 1C and 1D show intermediary states, and FIG. 1E is a steady state. The placement of a workpiece  133  is on surface  103  is shown in FIGS. 1B to  1 E. The material and surface finish of surface  103  are selected to provide a vacuum seal of each suction opening under the action of suction. Thus any initial leakage of air into a covered suction opening eventually seals off flow through that suction opening, while maintaining suction there. 
     Workpiece  133  covers suction opening  105  closest to port  111 , as well as suction openings  106  to  107  which are adjacent both to suction opening  105  and each other. The plumbing system  113  is configured to limit the application of suction to suction openings  105  to  108  that are either covered by or adjacent to workpiece  133  and have a path through open valves to port  111 . The sequential opening of the valves causes suction to be sequentially applied at the openings, and this imparts a suction force on the workpiece that moves along the workpiece as, resulting in an increasing suction force. This aspect of the present invention provides the benefit of limiting stresses on fragile workpieces. Prior to the application of vacuum, valves  123  to  126  are in the closed state shown in FIG.  1 B. When vacuum is supplied to port  111 , plumbing system  113  adapts to the placement of workpiece  133  by increasing the application of suction to an increasing number of suction openings, one suction opening at a time. The pressure in each chamber  114  to  118  is initially at ambient pressure. The application of vacuum at port  111  evacuates chamber  114 , which is substantially sealed by the workpiece at suction opening  105  and the initially closed valve  123 . This produces suction only at suction opening  105 . 
     When the pressure in chamber  114  approaches the vacuum pressure, valve  123  transitions to an open setting, as shown in FIG. 1C, and chamber  115  begins to evacuate. The valves are configured to automatically open based on the pressure difference between two adjacent chambers. Workpiece  133  is covering suction opening  106 , restricting flow there, while valve  124  is in the initially closed state. Thus suction is supplied to suction openings  105  and  106 . The pressure in chamber  115  decreases, eventually reaching a pressure low enough to cause valve  124  to open, as shown in FIG.  1 D. At this point suction is supplied to suction openings  105  to  107 . Chamber  116 , sealed by the initially and still closed valve  125  and workpiece  133  at suction opening  107 , then evacuates until the pressure in chamber  116  is low enough to open valve  125 , as shown in FIG.  1 E. As chamber  117  evacuates, leakage occurs at unsealed suction opening  108 . Valve  126  is configured to remained in the closed state when there is leakage at suction opening  108 , and so at the sequential opening of valves ceases. Workpiece  133  is held on by the sequential application of suction at suction openings  105 ,  106  and  107 , and the plumbing system need only contend with the vacuum leak at suction opening  108  and any slight leakage that may be occurring at the less-than-perfect vacuum seals at suction openings  105  to  107 . The sequential opening of the valves terminates at the opening of valve  125 . In a case not shown in the figures, an alternate workpiece also covers suction opening  109  (but as in the above case, not suction opening  108 ). In this alternate case, no suction force would occur at suction opening  109  since the sequential opening of the valves terminates at the opening of valve  125 . 
     The sequential action of valves  123  to  126 , and the resulting application of suction to suction openings  105  to  109 , defines a “line of connection” of the vacuum system that is reflected in the sequential application of suction to suction openings along that line, as illustrated in FIGS. 1A-1E. Each valve is in a normally closed state, and is opened by a pressure increase along the line of connection. The various interconnections, bores and valves making up plumbing system  113  are designed so that under the application of a vacuum, pressure drops are larger across bores than across interconnects or valves. On application of a vacuum, all valves  123  to  126  are in a closed state. The sequential evacuation of chambers, and the resulting sequential application of suction to the suction openings associated with each chamber defines the direction of the line of connection. 
     An important design criteria is that the pressure variations and valve actuations in plumbing system  113  are designed so that the next valve further along the line of connection, valve  126  in FIGS. 1A-1E, remains closed. In other words, the valves are designed to open when all suction openings between the valve and the vacuum source along the line of connection are covered. If one of the suction openings is uncovered, the pressure difference across the valve is too small for the valve to open, and the vacuum is not continued further down the line of connection. By this operation vacuum losses are limited to one suction opening at a time along the line of connection. It is important that the workpiece cover the suction opening closest to the vacuum source for this configuration to operate properly. The invention as presented in FIGS. 1A-1E is illustrative of the method of operation of the present invention, and is not meant to limit this invention to the configuration shown. For example, vacuum surfaces of the present invention may have one or more multiple lines of communication. 
     Lines of Connection Embodiments 
     Top views of the support surface  103  of several useful configurations of the present invention are shown in FIGS. 2A-2E. The views in FIGS. 2A-2E are perpendicular to surface  103 , and thus are the plan view of a vacuum plate or a view of an unrolled cylindrical vacuum cylinder. Vacuum bores connecting the suction openings to chambers run perpendicular to surface  103 , and thus are not visible in these views. 
     A linear array of lines of connection are shown in FIG.  2 A. This configuration has four independent lines of connection, each with four suction openings. Thus the Row 1 Line of Connection runs from a vacuum port  210  through a series of four suction openings  211  to  214 . Vacuum port  210  is capable of connection to a vacuum source (not shown). Also shown in FIG. 2A in broken lines are the important sub-surface plumbing components, specifically chambers  211 C to  214 C, interconnects  211 I to  214 I, and valves  211 ′ to  213 ′. The Row 2 Line of Connection runs from a vacuum port  220  through a series of suction openings  221  to  214 . This pattern repeats for the Row 3 Line of Connection with a vacuum port  230  and suction openings  231  to  234 , and the Row 4 Line of Connection with a vacuum port  240  and suction openings  241  to  244 . There is a chamber and interconnect associated with each suction opening, and thus there one valve between each suction opening (or between each set of openings in embodiments that have a set of more than one bores and suction opening for each chamber). Each interconnect and valve combination between two chambers along a line of connection forms a passageway that is controllable to be open or closed. The number of rows, the number of suction openings per row, and the exact layout of the suction opening pattern are for illustrative purposes are not meant to limit the possible embodiments of this invention. The outline of workpiece  250  on surface  103  is shown covering suction openings  211 ,  212  and  221 . Holes  211  and  212  are the first two suction openings in the Row 1 Line of Connection closest to port  210 , and suction opening  221  is the first suction opening in the Row 2 Line of Connection closest to port  220 . No suction openings in Row 3 or 4 are covered by workpiece  250 . The application of vacuum to this system with the workpiece shown will result in suction being applied to all of the suction openings  211 ,  212 , and  221  covered by workpiece  250 . Because the valves are designed to open only the next suction opening along each line of connection, leakage of the vacuum system will occur only at the suction openings  213 ,  222 ,  231 , and  241 . Valves  211 ′,  212 ′, and  221 ′ are shown open, their steady state after the vacuum is applied with this workpiece. For this embodiment and workpiece, the vacuum system must only contend with four open suction openings. 
     This should be contrasted with non-adaptable, prior art systems (not shown) which have non adaptable internal valves, and would thus have thirteen open suction openings ( 213  to  214 ,  222  to  224 ,  231  to  234  and  241  to  233 ). This also should be contrasted with the Kleinman system of above-mentioned U.S. Pat. No. 5,374,021, wherein each chamber has a valve between the chamber and the suction opening, the valve configured to be normally open, to be closed by application of the vacuum when the associated suction opening is uncovered, and to remain open when the associated suction opening is covered by the workpiece. With the Kleinman arrangement, each chamber is evacuated, requiring a large initial vacuum. Thus all the chambers form a large vacuum chamber which typically is the size of the surface rather than the workpiece, whereas in the present invention, the chambers form a larger chamber that adapts in size according to the dimensions of the workpiece. Furthermore, with the Kleinman system, the workpiece needs to be on the surface prior to application of the vacuum, otherwise those valves not covered by the workpiece will close when the vacuum is applied, resulting in essentially no force on that suction opening. With the present invention, the vacuum may already be on when the workpiece comes in contact with the support surface, providing advantages when picking up objects. Furthermore, with the Kleinman system, a suction force will be imparted simultaneously on all openings covered by the workpiece, whereas suction force is applied sequentially in the various embodiments of the present invention. 
     A top view of a multiply interconnected line of connection rectangular array is shown in FIG.  2 B. This configuration the support surface  103  is shown with one vacuum port  210 . Also shown in FIG. 2B in broken lines are the important sub-surface plumbing components, such as chambers, interconnects and valves. The embodiment in FIG. 2B is distinguished over that in FIG. 2A in that some of the chambers are connected to more than one other chamber, leading to bifurcations in the lines of connection. Specifically, chambers  211 C,  221 C, and  231 C, which are associated with suction openings  211 ,  221 , and  231 , respectively, are multiply connected. The lines of connection thus bifurcate at suction openings  211 ,  221 , and  231 . Chamber  211 C is connected through interconnect  212 I to chamber  212 C by valve  211 ′, and to chamber  221 C through interconnect  221 II by valve  211 ″. A similar configuration valves chamber  221 C to chambers  222 C and  231 C and also valves chamber  231 C to chambers  232 C and  241 C. As a result of this configuration, the Row 1 Line of Connection runs through openings  211  to  214 , the Row 2 Line of Connection runs through the opening sequence  211 - 221 - 222 - 223 - 224 , the Row 3 Line of Connection runs through the opening sequence  211 - 221 - 231 - 232 - 233 - 234 , and the Row 4 Line of Connection through the opening sequence  211 - 221 - 231 - 241 - 242 - 243 - 244 . The multiple valves per chamber work independently of one another, thus suction openings will open sequentially down the lines of connection until an uncovered suction opening is encountered. As a result, uncovered suction openings at bifurcation points will limit the application to suction along both lines of connection emanating from the bifurcation point. 
     The outline of workpiece  250  on surface  103 , covers three suction openings,  211 ,  212 , and  222 , providing suction to the workpiece, while only three suction openings  213 ,  222 , and  231  result in leakage to the vacuum system. Valves  211 ′,  211 ″,  221 ′,  221 ″, and  212 ′ are shown open, their steady state after the vacuum is applied with this workpiece. This should be contrasted to the FIG. 2A layout, where the same suction opening pattern and workpiece shape and placement resulting in leakage occurred through four suction openings. The multiple branching down the rightmost suction openings limits the number of rows down which the suction force is applied. 
     FIG. 2C is a top schematic view of a third embodiment that has a rectangular layout where both rows and columns are diagonally interconnected. Also shown in FIG. 2C in broken lines are the important sub-surface plumbing components, such as chambers, interconnects and valves. The main line of connection runs diagonally from port  210  sequentially through the opening sequence  211 - 222 - 233 - 244 . Each of chambers  222 C,  233 C, and  244 C has three valves, trifurcating the lines of connection at those points. Chamber  222 C is equipped with valves  222 ′,  222 ″, and  222 ′″, splitting the lines of connection to a Line of Connection A that runs through the opening sequence  211 - 222 - 212 , a Line of Connection D that runs through opening sequence  211 - 222 - 221 , and a continuing line that runs diagonally to chamber  233 C. Chamber  233 C has valves  233 ′,  233 ″, and  233 ′″, trifurcating the line of connection to Line of Connection B, with opening sequence  211 - 222 - 233 - 223 - 213 , Line of Connection E with opening sequence  211 - 222 - 233 - 232 - 231 , and a continuation of the line of connection to chamber  244 C. The line further bifurcates at chamber  244 C through the multiple valves  244 ′and  244 ″ into Lines of Connection B and F. 
     The FIG. 2C embodiment illustrates the usefulness of modifying the lines of connection to expected workpiece shapes. By aligning the lines of connection it is possible to configure the vacuum surface to restrain a large number of difference workpiece shapes with loss of vacuum at only one suction opening. The embodiment of FIG. 2C is particularly useful in minimizing vacuum losses for workpieces  252  or  254  that cover the square suction opening pattern defined by the lines of connection. Thus workpiece  252  is restrained by suction at suction openings  211 ,  212 ,  221 , and  222 , while leakage only occurs at suction opening  233 . Workpiece  254  will likewise result in leakage only at suction opening  244 . 
     The embodiment in FIG. 2D has circular lines of connection pattern. Center suction opening  260 , through chamber  260 C, is connected to a vacuum port (not shown) at a location below surface  103 . Primary suction openings  270 ,  280 , and  290  are connected by vacuum bores (not shown) to chambers  270 C,  280 C, and  290 C, located at a first, second, and third radial location, respectively. The primary suction openings are connected to center suction opening  260  through sub-surface interconnects  260 I,  270 I,  280 I, and  290 I, chambers  260 C,  270 C,  280 C, and  290 C, and valves  260 ′,  270 ′,  280 ′, and  290 ′. The suction opening pattern further comprises a set of secondary suction openings  270 - 1  to  270 - 5  at the first radial location, a set of secondary suction openings  280 - 1  to  280 - 7  at the same second radial location, and a set of secondary suction openings  290 - 1  to  290 - 11  at the same third radial location. Chambers  270 C and  280 C are equipped with two valves each, causing the lines of connection to bifurcate at those points. At each radial location, suction openings are connected thought interconnects, valves, chambers and bores to form circular lines of connection that pass through the primary suction openings. Thus the primary line of connection is through opening sequence  260 - 270 - 280 - 290 . The resulting lines of connection  1 ,  2  and  3  are shown in FIG.  2 D. The lines of connections run from suction opening  260  to circular Lines of Connection  1  (“LOC 1 ”) at the radii of suction opening  270 , circular Line of Connection  2  (“LOC 2 ”) at the radii of suction opening  280  and the circular Line of Connection  3  (“LOC 3 ”) at the radii of suction opening  290 . All other suction openings are connected through a chamber, interconnect and valve to an adjacent suction opening. 
     A circular workpiece  291  centered on suction opening  260  will result in suction being applied to all suction openings covered by the workpiece, specifically suction opening  260  and all suction openings at the radii of suction opening  270 , while leakage will only occur at suction opening  280 . This embodiment is thus seen to be particularly useful for restraining circular workpieces centered on the line of connection suction opening pattern. 
     An example of an embodiment with multiple suction openings per valve is presented in FIG.  2 E. This embodiment has the same suction opening pattern as the embodiment in FIG.  2 D. Holes  260 ,  270 ,  280 , and  290  are connected though chambers, interconnects, and valves to the next suction opening. All secondary suction openings at each radii are connected without valves, effectively allowing a plurality of suction openings to be controlled with each valve. Thus chamber  270 C has 6 suction openings, all of which are activated by valve  260 ′, and chamber  280 C has 8 suction openings, all actuated by valve  270 ′. This configuration has less valves and is thus simpler than previous embodiments. The placement of workpiece  291  will provide suction at suction opening  260  and all suction openings at the radii of suction opening  270 . Valve  280 ′ will remain closed, producing a loss of vacuum at all  8  suction openings connected to chamber  280 C. 
     Other planar arrangements also are possible, including, for example, using one or more lines of connection that follow a spiral pattern. 
     Methods of Assembling Adaptable Vacuum Surfaces 
     One simple method of constructing an adaptable vacuum surface in accordance with the present invention is shown in FIGS. 3 and 4. The configuration shown in FIGS. 3 and 4 shows an implementation of the singly connected chambers, as illustrated in the embodiments of FIGS. 1 and 2A. Furthermore, the extension of the construction method outlined here to the multiply connected chambers embodied in FIGS. 2B through 2E is straightforward given the description of the present embodiment. 
     The present invention is shown in FIG. 3A without a workpiece and in FIG. 3B with a workpiece  333  covering some of the suction openings. The vacuum holder  101  of FIG. 3 includes a workpiece-bearing member  301  (a metal plate, for example), a cover member  315  (e.g., a cover plate), and a resilient gasket  323  sandwiched between workpiece-bearing member  301  and cover member  315  and held in place through a gasket compression mechanism  331 . The gasket is made of a single sheet of rubber or other suitable resilient material. The workpiece-bearing member and cover members are preferably made of steel. Compression mechanism  331  can comprise a set of clip springs as shown in FIG. 3, or in other embodiments includes screws (or nuts and bolts) though both members to provide compressive force. The construction is such that mechanism  101  can maintain structural integrity under the force of the vacuum. Workpiece support surface  103 , located on the exposed surface of workpiece-bearing member  301 , should be materially compatible with the workpiece material, and the application of suction to the suction openings should provide an airtight seal by the workpiece across the suction openings. While polished steel is used in the preferred embodiment, a variety of metallic and plastic materials and coatings on various materials meet these criteria, as would be clear to those in the art. 
     Cover member  315  is in contact with gasket  323  at a cover member gasket surface  317 . Cover member gasket surface  317  has a plurality of chambers  319  formed by cavities in surface  317 . At least one of chambers  319  is connected to a vacuum port  321 , providing the suction force needed for this invention. One side of workpiece-bearing member  301  has a plurality of suction openings  307  located on surface  103 . Each suction opening  307  is connected by a vacuum bore  305  to a workpiece-bearing member gasket surface  303 . Each of vacuum bores  305  is aligned both with one of gasket suction openings  325  extending through gasket  323  and one of chambers  319  (in alternate embodiments, a set of openings on the surface is connected to each chamber  319 ). Connections between chambers are made by a plurality of channels  309  formed by cavities in the workpiece-bearing member gasket surface  303 . Channels  309  are aligned to overlap the edges of adjacent chambers  319 . One end of each channel, the open channel end  311 , is connected to a chamber  319  through gasket channel suction openings  327 . The opposite, valved channel end  313 , is connected to an adjacent chamber  319  by a gasket flap  329  in gasket  323  that defines a valve. Gasket flap  329  is formed through a partially cut-out section of gasket  323  that in its closed state covers the entire valved channel end  313 , and in its open state folds into chamber  319  given a sufficient over-pressure in channel  309  relative the pressure in chamber  319 . Gasket flaps  329  thus each define a valve biased to be closed, and allowing, when open, air to be suctioned through connected chambers towards vacuum port  321 . 
     A top view of a section of gasket  323  that services two adjacent chambers  319  is shown in FIG.  4 . The location of the edges of chambers  319  are shown as chamber edges  401  and  403 . There is gasket suction opening  325  located within each chamber edge. The location of the edge of the channel  309  that connects the two chambers is shown as channel edge  405 . Note that chamber edges  401  and  403  and channel edge  405  are on the opposite sides of gasket  323 . Edge  401  in this view is located closer to vacuum port  321  (not shown) than is edge  403 . The channel end closest to vacuum port  321  is the valved channel end  313 , located within chamber edge  401 , while the channel end farthest from port  321  is the open channel end  331  and is located within chamber edge  403 . A gasket channel suction opening  327  is located within chamber edge  403  forming the open channel connection. Gasket flap  329  is positioned to cover valved channel end  313  when in the closed state, and to also be included in chamber edge  401  so that the flap can open into the chamber providing a path for communication between chambers. 
     The cavities, suction openings and flaps in members  301  and  315  and gasket  305  can perform the functions described previously regarding the action of the mechanism shown in FIGS. 1 and 2. The action of the valves to a workpiece  333  is shown in FIG. 3B When a vacuum is applied to port  321 , valves along the line of communication, traveling away from port  321  are sequentially opened. Valves  329  open into chambers  319  providing a passage of ambient air through suction openings  307  towards port  321 . The embodiment presented here can be modified to include multiple channels per suction opening, allowing for multiple lines of connection, and can likewise be configured without gasket flaps between selected chambers to allow the mechanism to have multiple suction openings per valve. These combinations will allow for any of the embodiments presented in FIG.  2 . 
     It is interesting to contrast the embodiment of FIGS. 3 and 4 with an embodiment of the Kleinman system described in above-mentioned U.S. Pat. No. 5,374,021 and shown in FIG.  5 . FIG. 5A is a longitudinal sectional view of vacuum table  501 , and FIG. 5B is a fragmentary, exploded view of the vacuum table of FIG.  5 A. Vacuum table  501  has a rigid base member  502 ; a partition member  503  thereover; a spacer member  504  thereover; a sheet  505  thereover defining a plurality of valve members; and an upper panel  506  formed with a plurality of suction openings ( 561 ) and adapted to receive and hold a workpiece (e.g., a printed circuit board PCB) thereon. The vacuum table  501  is adapted to be connected to a vacuum source  508  via a vacuum tube  509 . The rigid base member  502  is formed with a plurality of upwardly-facing cavities  521 , each circumscribed by a wall  522  formed with a slot  523  such that the cavities  521  are always interconnecting. Base member  502  is further formed with an opening  525  connected by vacuum tube  509  to the vacuum source  508 . The partition member  503  with the cavities  521  of base member  502  thus form a plurality of vacuum sub-chambers interconnected by slots  523 . The partition member  503  has an opening  531  for each of the vacuum sub-chambers  521 . The smaller openings  532  are to assist in adhesively bonding the partition member to the rigid base  502  and to the overlying spacer member  504 . 
     Spacer member  504  is also in the form of a sheet. It has a plurality of cut-outs  541  of the same configuration as, and aligned with, one of the vacuum sub-chamber cavities  521  formed in the rigid base member  502 . Thus, control passageway openings  531  are formed in the partition member  503  and are each located centrally of one of the vacuum sub-chamber cavities  521 , and centrally of one of the cut-outs  541  in the spacer sheet  504  on the opposite side. 
     The valve member sheet  505  overlying the spacer member  504  is formed with a plurality of valve members  551  for, and aligned with, each of the control passageway openings  531  formed in the partition member  503 . Each of the valve members by valve member  551   a ,  551   b ,  551  is of planar configuration, and is integrally formed with an elastic juncture section  552 , and a common outer frame  553 , which serves as a mounting section for all the valve members. 
     The upper panel  6  included in the vacuum table is formed with the plurality of suction openings  561  through which suction is applied for holding the article PCB on the table. 
     The valve members  551 , in their normal unstressed condition, are substantially coplanar with their common frame  553 ; that is, their juncture sections  552  are not bent. Thus, the valve members  551  are normally biased to the position illustrated by valve member  551   a  in FIG. 5A, opening its respective connecting passageway  531   a . When the vacuum source  508  is applied to the interconnecting sub-chambers, the vacuum will apply a force displacing the valve members  551  towards their respective connecting passageways  531  to close those passageways, as illustrated by valve member  551   b  closing passageway  531   b  in FIG.  5 A. This displacement of the valve members  551  will occur only with respect to all the connecting passageways communicating with suction openings  561  not covered by the article PCB on the table. Thus, those suction openings  561  not covered by the printed circuit board PCB will have no vacuum applied. However, the suction openings  561  covered by the printed circuit board will remain in communication with their respective connecting passageway. Accordingly, the vacuum from the respective sub-chamber cavity  521  will be applied via connecting passageway  531  to the suction openings  561  communicating with that connecting passageway via the outlet chamber defined by the cut-out  541  in spacer member  504 , thereby firmly holding the workpiece PCB to the table. 
     As previously pointed out, the Kleinman system has several shortcomings in comparison with the present invention. In addition, the construction of the Kleinman system shown in FIG. 5 is more complex than the construction of the embodiment of the present invention shown in FIGS. 3 and 4. More layers are involved, these need to be accurately aligned, and the having a normally open valve made with a movable flap of a resilient material closing a hole on another material is more prone to problems than having a normally closed valve defined by a cut on a resilient sheet. Thus, the Kleinman construction shown in FIG. 5 is more difficult to construct, liable to be more expensive, and liable to be more problematic. 
     Several variations of the present invention are possible. Several suction openings may be used for each chamber. Also, surface patterns such as cross-grooves on the surface may be used to improve the suction force and contact, as is known in the art. For example, the suction openings may end on the workpiece support surface in a grooved pattern to optimize suction force towards the workpiece being held. Such improvements are within the scope of the invention. The inventive automatically adapting vacuum system described herein thus can be applied to any type of suction opening and surface structure, and how to modify the embodiments described herein to incorporate such features would be clear to those in the art. 
     Hence, although this invention has been described with respect to preferred embodiments, those embodiments are illustrative only. No limitation with respect to the preferred embodiments is intended or should be inferred. It will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of the invention, and it is intended that the scope of the invention be defined by the claims appended hereto.