Abstract:
The present invention refers to a novel apparatus and method to restrict pneumatic flow in a planar manifold. A forming tool of specific geometry is pressed into a planar manifold causing the pneumatic channel inside to collapse onto itself in a predictable and controllable way, therefore restricting the fluid flow in the pneumatic channel. The geometry of the forming tool is provided with angles and radii so that the planar manifold is not ripped during the pressing operation. Further, the geometry limits the deformed area so that distortion of adjacent pneumatic channels, and the potential for springing leaks between layers is minimized. In a preferred embodiment, the tooling also provides flow measurement while the forming tool is pressed into the planar manifold at a specific orientation.

Description:
FIELD OF INVENTION 
     The present invention relates to methods and apparatus for controlling a fluid stream in a pneumatic assembly. 
     BACKGROUND OF THE INVENTION 
     Modem analytical instrumentation, such as a gas or liquid chromatograph, often requires accurate control of a fluid stream. Such instruments can employ one or more fluid streams in respective flow paths, and an extensive and complex array of channels, tubing, and fittings that are necessary for controlling the fluid flow. In addition, there is often a need to sense certain characteristics of the fluid at different points in the flow paths, such as the pressure, flow rate, and temperature of the fluid. These needs are typically addressed by the attachment of different sensors to the flow path, further increasing the complexity and physical volume of the flow system. 
     Diffusion bonded planar manifold technology offers a solution that simplifies the flow system. By eliminating the connecting tubing and fittings between different components, diffusion bonded planar manifolds provide a flow system that is compact, easily-manufactured, and reliable. A further advantage of diffusion bonded planar manifolds is that multiple fluid-handling functional devices may be coordinated and assembled in a small volume. This advantage results from pneumatic channels which are integrated into the diffusion bonded planar manifold, and which provide the fluid flow paths. The diffusion bonded planar manifold is also quite compact and amenable to construction in a variety of shapes and configurations, helping to minimize the volume of the flow system. However, the different flow paths in a diffusion bonded planar manifold often have balanced, or different flow rates which need to be controlled precisely for optimal performance of the instrument. 
     Commonly used devices for restricting fluid flow rates include discrete flow restrictors and fine bore tubing. Flow restrictors (“frits”) are made of powder metals that are pressed or sintered into various porosity and shapes to provide the required pneumatic resistance. FIG. 1 shows a schematic representation of a porous metal frit in a pipe. The fluid flow enters at a high pressure and leaves at a lower pressure due to the pressure drop created across the frit element. 
     Flow restrictors are provided in holders, which are usually installed with elastomer seals. Alternately, flow restrictors are provided in various geometries that can be pressed into an assembly. In either case, flow restrictors are a separate part and require machined features, seals and/or fastening hardware to install. It is difficult to integrate flow restrictors into a thin diffusion bonded planar manifold without external seals or fastening hardware. 
     Fine bore tubing is available with thicker walls to provide small internal diameters and therefore pneumatic resistance if a long enough length is used. Fluid pressure drops as a function of fluid velocity and properties, tubing diameter and length, and friction due to pipe finish, fittings, and diameter changes. However, fine bore tubing also requires fastening hardware to install, and the size of tubing is usually larger than all the other features on a diffusion bonded planar manifold. 
     An alternative method to restrict flow is to reduce channel sizes in a diffusion bonded planar manifold. Restrictance by channel width (diameter) on diffusion bonded manifold plates, however, is limited by the etching and plating dimensions and the raw stock thickness. To date, pneumatic channels in diffusion bonded planar manifolds have been enlarged in size to provide more flow, but not decreased in size to restrict flow, because metal sheets with very small diameter channels are difficult to handle and prone to plugging during the bonding process. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and an apparatus to restrict flow rate in a diffusion bonded planar manifold with multiple, adjacent pneumatic channels. A forming pen with a bit is pressed into a diffusion bonded planar manifold causing the pneumatic channel inside to collapse onto itself in a predictable and controllable way. The bit has a geometry with angles and radii chosen or designed so that the surface of the diffusion bonded plate is dimpled but not ripped during the pressing operation. Further, the geometry of the bit limits the deformed area so that distortion of adjacent pneumatic channels is minimized, and the integrity of the deformed pneumatic channel and adjacent pneumatic channels is maintained (e.g., the pneumatic channels do not leak). No external seals or extra parts are required. 
     In a preferred embodiment, the apparatus also provides holding devices for the forming pen and/or the diffusion bonded planar manifold, as well as a pressing device to better control the pressure applied to the forming pen. In yet another preferred embodiment, the diffusion bonded planar manifold is connected to a regulated air supply and a flow meter so that the flow rate in the targeted pneumatic channel is monitored while the forming pen is pressed into the diffusion bonded planar manifold at a specific orientation. The method and apparatus disclosed herein may also be utilized to restrict flow rate in other types of planar manifolds, so long as they have a material property that allows plastic deformation without tearing or too much elastic springback. 
     These and other advantages will become obvious to those skilled in the art upon review of the following description, the attached drawings and appended claims. Although a preferred embodiment of the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a prior art method of restricting flow rate by a flow restrictor. 
     FIGS. 2 a - 2   e  show a preferred embodiment of a forming pen. 
     FIG. 3 is a side perspective view of a deforming apparatus. 
     FIG. 4 is a block diagram of a deforming apparatus with an air supply and a flow meter. 
     FIG. 5 is a flow chart showing the deforming process. 
     FIG. 6 is a front view of the interior side of a diffusion bonded planar manifold. 
     FIG. 7 is a diagram showing the restriction of a pneumatic channel during the deforming process. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2 a - 2   e  show a forming pen  200  comprising a shank  202  and a bit  204 . The forming pen&#39;s length (L) is usually greater than its width (W). Preferably, the length L may be in the range of about 15 mm to about 60 mm, and the width may be in the range of about 3 mm to about 8 mm. The bit  204  may be formed on one end of the shank  202 . Alternatively, the bit  204  may be made of a material different from the shank  202  and may be attached to one of the ends of the shank  202 . The bit  204  has one or more side surfaces  206  tapered inward with tapering angles θ varying from about 0° to about 75°, and preferably from about 30° to about 55°, relative to the longitudinal axis of the shank  202 . The tapered side surface(s)  206  ends at a tip  208 , which is preferably perpendicular to the longitudinal axis of the shank  202 . The bit  204  may be made of any material of suitable hardness greater than the hardness of the material that constitutes the targeted area on the diffusion bonded planar manifold (not shown). The bit  204  is designed with such a geometry (i.e., the size and shape of the tip  208 , and the tapering angles θ of the side surface(s)  206 ) so that the surface of the diffusion bonded planar manifold is dimpled but not ripped during the deforming operation. Further, the geometry limits the deformed area so that distortion of adjacent pneumatic channels, and the potential for springing leaks between the bonded layers or between pneumatic channels of the diffusion bonded planar manifold, is minimized. 
     In the embodiment shown in FIG. 2 a , the forming pen  200  is made of stainless steel. The forming pen  200  has a rod-like shank  202  and a bit  204  which is formed from the shank  202  at one end. As shown in FIGS. 2 b  and  2   c , the length L of the forming pen  200  is about 38 mm and the width W (in this case the diameter) of the forming pen  200  is about 4.1 mm. The bit  204  is about 2.2 mm long and has four side surfaces. Side surfaces  206 ,  206 ′,  206 ″, and  206 ′″ taper inward with a tapering angle of about 45° and end at tip  208 , which has a nominally rectangular shape of about 0.4 mm (between surfaces  206  and  206 ′) by 2.1 mm (between surfaces  206 ″ and  206 ′″). All edges joining surfaces  206  and  208  are preferably smooth transitions of radius up to 1 mm in order to minimize tearing or scratching of the diffusion bonded plate during deformation. The smooth transitions may be made by polishing off edge sections  210  (FIG. 2 d ) and  212  (FIG. 2 e ) of the bit  204 . 
     When the bit  204  of the forming pen  200  is pressed against the surface of a diffusion bonded planar manifold at a targeted pneumatic channel, the bit  204  deforms the surface and causes the targeted pneumatic channel under the surface to collapse onto itself, thereby restricting the fluid flow inside the targeted pneumatic channel. A holding device may be used to place the forming pen  200  at a desired position and with a desired angle relative to the diffusion bonded planar manifold. If the position of the area to be operated upon (i.e., the area where the targeted pneumatic channel is located) is not marked on the outer surface of the diffusion bonded planar manifold, specially designed holding tools may be needed in order to orientate the forming pen  200  to the targeted area on the diffusion bonded planar manifold. A pressing device, such as an arbor press, may be used to apply a controllable and measurable force to the forming pen  200 . In a preferred embodiment, a regulated air supply and a flow meter are connected to the diffusion bonded planar manifold so that the flow rate in the targeted pneumatic channel is monitored during the deforming process. In this setting, the force applied to the forming pen  200  may be adjusted based on the flow rate so as to prevent over-restriction of the targeted pneumatic channel in the diffusion bonded planar manifold. 
     FIG. 3 shows a deforming apparatus  300  that includes a forming pen  200  and a holding device  300  comprising a pen holder  302 , a top plate  304 , a upper stop  306 , a top compression block  308 , a bottom compression block  310 , and a base plate  312 . The top compression block  308  and the bottom compression block  310  hold registration pins  314  and  316 , dowels  318  and seals (not shown) for a precise alignment of the compression blocks  308 ,  310  with the diffusion bonded planar manifold  400 , which is sandwiched between the compression blocks  308  and  310 . A number of o-rings (not shown) in various pockets on the bottom surface of the top compression block  308  and on the top surface of the bottom compression block  310  create seals to the targeted pneumatic channel in the diffusion bonded planar manifold  400 . A cap screw  340  goes through a hole  336  to fasten the top compression block  308 , the diffusion bonded planar manifold  400 , and the bottom compression block  310  together. The top compression block  308  also provides an inlet port  320  for the connection to an air supply (not shown) and an outlet port  322  for the connection to a flow meter (not shown). The pen holder  302  clamps the forming pen  200  in a fixed orientation. A clamp screw  324  closes the split collar at the end of the pen holder  302  to lock orientation of the forming pen  200 . The bit  204  of the forming pen  200  is placed in a hole  338  on the top compression block  308 . A bushing  326  provides further alignment and orientation for the forming pen  200  relative to the top compression block  308 . Preferably, the longer side of the tip  208  (i.e., the side where the surface  206  meets the tip  208 , FIG. 2 c ) is aligned to a centerline of the targeted pneumatic channel. The pen holder  302  itself is oriented by a pen holder alignment dowel  328 . A button  330  provides a hardened surface for the forming pen  200  at the bottom. The deforming of the diffusion bonded planar manifold can be performed manually by applying force to the upper end of the forming pen  200  with an arbor press (not shown) on the partially assembled deforming apparatus  300 ′, which comprises the forming pen  200 , the pen holder  302 , the top compression block  308 , the bottom compression block  310 , and the diffusion bonded planar manifold  400 . 
     Alternatively, the deforming process can be performed by a standard pneumatic dieset press (not shown) using the deforming apparatus  300 . In this case the upper stop  306  is placed on top of the forming pen  200  to provide a hardened surface. The top plate  304  and the base plate  312  facilitate holding of the partially assembled deforming apparatus  300 ′ by a standard press (not shown). The upper stop  306  is fastened to the top plate  304  by screws  332 . A threaded stop  334  provides experimental hard stop for experimental fixed deflection evaluation. 
     FIG. 4 is a block diagram of a deforming apparatus with an air supply and a flow meter. From the air supply  402 , a tube  404  leads to a pressure regulator  406  with an attached gage  408  that regulates the pressure to a desired range, for example, 5-10 psi. In a preferred embodiment, 6 psi was chosen to keep the before and after flow rates within the dynamic range (1-1000 ml/min) of the flow meter. The outlet of the pressure regulator  406  is connected to the deforming apparatus  300  or the partially assembled deforming apparatus  300 ′ through an inlet fitting  410  which is fastened to the inlet port  320  (not shown in FIG.  4 ). A flow meter  414  is connected to the deforming apparatus  300  or the partially assembled deforming apparatus  300 ′ through an outlet fitting  412  which is fastened to the outlet port  322  (not shown in FIG.  4 ). 
     A pressured air from the air supply  402  is fed through the tube  404  and the pressure regulator  406 , through the inlet fitting  410  and the inlet port  320  on the top compression block  308 , through the o-rings making a seal between the diffusion bonded planar manifold  400  and the top compression block  308 , through the pneumatic channel being operated upon, and through another o-rings between the diffusion bonded planar manifold  400  and the top compression block  308  to the outlet port  322 , and finally reaches the flow meter  414  through the outlet fitting  412 . 
     FIG. 5 illustrates an embodiment of a method  500  used to restrict the flow rate in a pneumatic channel of a diffusion bonded planar manifold. The method  500  preferably comprises the following steps: positioning  502  the forming pen and the diffusion bonded planar manifold in a holding device, connecting  504  a regulated air supply and a flow meter to the holding device, providing  506  an air pressure in the targeted pneumatic channel with the air supply, recording  508  an initial flow rate in the targeted pneumatic channel with the flow meter, pressing  510  the forming pen into the diffusion bonded planar manifold, observing  512  the flow rate drop in the targeted pneumatic channel, retracting  514  the forming pen when the flow rate in the targeted pneumatic channel is a desired flow rate, recording  516  the flow rate in the targeted pneumatic channel after the retraction of the forming pen, calculating  518  a springback differential flow and a compensating flow rate by the following formula: 
     
       
         Springback differential flow=recorded flow rate−desired flow rate, 
       
     
      Compensating flow rate=desired flow rate−springback differential flow, 
     pressing  520  the forming pen into the diffusion bonded planar manifold again until the flow rate in the targeted pneumatic channel is the compensating flow rate, and retracting  522  the forming pen to validate that the final measured flow rate is within a tolerable range of the desired flow rate. 
     EXAMPLE 1 
     Restricting Flow Rate in a Branch of the Electronic Pressure Control (EPC) in a Micro-GC Manifold 
     This example demonstrates how a partially assembled deforming apparatus  300 ′ is used to restrict flow rate in a diffusion bonded planar manifold  400 . 
     FIG. 6 shows the interior side of a diffusion bonded planar manifold  400 . There are numerous pneumatic channels within the diffusion bonded planar manifold  400 . A pneumatic channel  610  connects the EPC output port  604  to a pressure sensor port  612 , to an injector die port  602 , and to a switch valve port  606  through a merging pneumatic channel  608 . The pneumatic channel  610  provides column flow to both reference and analytic columns on the injector die through port  602 . Pneumatic channels  608  and  610  merge at the pressure sensor port  612  which is used for control feedback taps. The pneumatic channel that needs to be restricted (i.e., the targeted pneumatic channel) is pneumatic channel  608 , and the approximate location of the dimple for restricting the pneumatic channel  608  is pointed to by arrow  608 . 
     The reason for the channel restriction is to achieve stability of the EPC (not shown in the figure), and to provide a stable baseline for the micro GC. During the injection process, the total column flow is approximately 4 ml/min, provided by perhaps 25 psi of pressure from port  606  to port  602 . At one point, the switch valve changes state and shares the EPC pressure through port  606  to perform an injector process, which creates a momentary high demand for carrier gas from EPC. This sudden drop in pressure causes the EPC to go out of control, causing undesired flow disturbance on the baseline output of the GC. 
     By limiting the flow to the switch valve (through pneumatic channel  608 ), the EPC can follow the temporary demand without introducing too much pressure noise on the primary column flow pneumatic channel  610  of the diffusion bonded planar manifold  400 . The objective is to reduce the air flow rate in the pneumatic channel  608  from 600-700 ml/min to about 55 ml/min at 6 psi. This rate restriction creates a smoother transition during compression, lower demand on an EPC control loop, and a smoother baseline on the GC output chromatogram. 
     Since the pneumatic channel  608  is connected to four ports  602 ,  604 ,  606  and  612 , ports  604  and  612  are sealed. Ports  602  and  606  serve as the inlet and outlet, respectively, for a flow measurement. As shown in FIG. 6, pneumatic channel  608  is in close proximity to another pneumatic channel  614 . Therefore, the deformed area has to be limited to the extent that the flow rate in the neighboring pneumatic channel  614  is not affected. Furthermore, the deformed area has to be limited to the extent that the seals made against the diffusion bonded planar manifold  400  by devices attached at ports  606 ,  608 , or  612  are not compromised by changes in surface finish or flatness. The deforming apparatus  300  in FIG. 3, which is specially designed for the diffusion bonded planar manifold  400 , positions the forming pen  200  at the middle point between the pressure sensor port  612  and the switch valve port  606 . The tip  208  is in close proximity and parallel to the surface of the manifold  400 , with the longer side of the tip  208  aligned to the centerline of the targeted pneumatic channel  608 . 
     The deforming process is performed with the following steps with references to FIG.  3 : 
     1. Loading the tool: 
     Open the partial holding device  300 ′ (without the diffusion bonded planar manifold  400 ) using a hex key on the clamp screw  340 , remove the top compression block  308  by sliding the top compression block  308  straight up, and make sure that the o-rings (not shown in the figures) stay in place. 
     Put the diffusion bonded planar manifold  400  over the dowels  318  so that the diffusion bonded planar manifold  400  is properly positioned on the bottom compression block  310 . Replace the top compression block  308  over the locating dowels without disturbing the location of the diffusion bonded planar manifold  400 . Replace and tighten the cap screw  340 . 
     Connect the pressure regulator  406  to the inlet port  320  through the inlet fitting  410 , connect the flow meter  414  to the outlet port  322  through the outlet fitting  412 . 
     Place the forming pin  200  into the hole  338  near the cap screw  340  and locate the partial assembly  300 ′ under the arbor for deforming. 
     2. Pressing the dimple: 
     Turn on the air supply and see that the pressure is about 6 psi. Turn on the flow meter  414  and observe the flow rate. The flow rate is typically 600 to 800 ml/min of air. 
     Begin pressing the forming pin  200  with the arbor press and observe the flow rate falling on the flow meter  414 . As the flow rate displayed on the flow meter  414  falls under 100 ml/min, increase the pressure slowly until the display on the flow meter  414  reads about 55 ml/min (the desired flow rate). Release the force and record the flow rate. Calculate the amount of change in flow due to springback by the following formula: 
     
       
         Springback differential flow=recorded flow rate−55. 
       
     
     The springback differential flow is usually between 5 and 12 ml/min in this particular embodiment. 
     Calculate the compensating flow rate by the following formula: 
     
       
         Compensating flow rate=55−Springback differential flow. 
       
     
     3. Re-dimple the diffusion bonded planar manifold: 
     Pressing with the arbor press again, increasing the pressure slowly until the flow rate falls to the compensating flow rate. Release the arbor press and record the flow rate on the flow meter  414 . This step may need to be repeated in order to reach an acceptable flow rate. 
     Acceptable Flow Rates 
     The desired flow rate is 55 ml/min. A flow rate of between 40 and 60 ml/min is acceptable for this procedure. 
     FIG. 7 demonstrates how the pneumatic channel  608  within the diffusion bonded planar manifold  400  collapses onto itself during the deforming process. The diffusion bonded planar manifold  400  used in Example 1 has a thickness of about 1 mm. The diameter of the pneumatic channels  608  and  614  within the diffusion bonded planar manifold  400  have a diameter of about 0.6 mm to about 0.7 mm. The distance between the two pneumatic channels is about 1.3 mm. When the pneumatic channel  608  is deformed by the forming pen  200 , the bit  204  is pressed against the surface of the diffusion bonded planar manifold  400  above the pneumatic channel  608 , causing the pneumatic channel  608  to collapse into a crest shape. When the bit  204  is pressed down further, the top of the pneumatic channel  608  reaches the bottom of the pneumatic channel  608 , dividing the pneumatic channel  608  into two much smaller pneumatic channels  608 ′and  608 ″ which results in a reduced fluid flow rate. The ratio between a pre-restriction flow rate and a post-restriction flow rate is defined as a “reduction rate”. For example, if the flow rate in a pneumatic channel is reduced from 500 ml/min to 50 ml/min by the deforming process, the reduction rate is 10:1. 
     FIG. 7 also demonstrates the importance of the geometry of the bit  204  during the deforming process. When the forming pen  200  is pressed into the diffusion bonded planar manifold  400 , the geometry of the bit  204  determines the extent of deformation of the targeted pneumatic channel  608  and therefore the restriction rate achieved through the deforming process. For example, a blunt bit  204  with tapering angles larger than 45° may result in a bigger dimple on the surface of the diffusion bonded planar manifold  400 , leading to more restriction on the pneumatic channel  608  and possibly deformation on the neighboring pneumatic channel  614  as well. On the other hand, a sharp bit  204  with tapering angles smaller than 45° may reduce the deformed area and result in less restriction on the pneumatic channel  608 .