Abstract:
The present invention provides systems and methods of dispensing liquids. In one embodiment, the system includes a pump with a removable pump module with at least one displacement piston and at least one piston valve. A motor and base assembly provides the supporting components of the pump, which can be used in environments where precise small volumes of ultra-pure liquids must be transferred from a reservoir to a point of use. The preferred embodiment of the system prevents contaminants and air bubbles from being introduced into the liquid to be dispensed by placing a filter across the discharge line downstream from the pump, and providing a separate drawback line for performing the drawback of the liquid in the dispensing nozzle.

Description:
This application is a continuation-in-part of application Ser. No. 09/360,851, filed Jul. 24, 1999, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to dispensing liquids in precise volumes and more particularly to the transfer of liquid from a reservoir to a point of use by a pump having a displacement piston and a rotating piston valve communicating with one of a plurality of liquid ports. 
     The ability to deliver precise small volume amounts of liquids without introduction of contaminants is quite important in the manufacture of many products, especially in the electronics industry. A semiconductor foundry has several principal areas-metrology, lithography, and track where resist and developer must be rapidly and precisely dispensed. More specifically, photolithography requires precise repeatable delivery of photoresist and developer at different rates such as volumes of 0-10 ml±0.1%, repeatable to within ±0.1 volume % with substantially no contaminants or air bubbles. If these requirements cannot be met consistently, it adversely impacts the yield of the process. See, e.g., Chang &amp; Sze,  ULSI Technology  (1996) hereby incorporated by reference. 
     The semiconductor industry provides, for example, different pumps such as piston pumps, diaphragm pumps, and peristalic pumps to transfer liquid from a liquid reservoir to a dispense nozzle above a silicon wafer in a spin station. After the liquid is dispensed any residual liquid left in the tip of the nozzle is drawn back slightly so that the resulting meniscus force prevents uncontrolled drips on the wafer and the wafer is rotated at high rpm to spread the liquid uniformly over the wafer. 
     The liquid dispensing system must also provide a filter to capture contaminants which might be introduced in the liquid dispensed. When the filter is upstream of the pump, it captures the contaminants generated for example at the reservoir and/or the reservoir line leading to the pump but will be ineffective at capturing contaminants generated in the pump which then enter the liquid dispensed on the wafer. When the filter is downstream of the pump, the filter may capture pump generated contaminants but may still release air bubbles and contaminants into the dispensing system during draw back mode when the liquid reverses direction through the filter, which tends to dislodge some of the particles caught in the filter. 
     SUMMARY OF THE INVENTION 
     The invention provides systems and methods of rapid delivery of liquids in precise volumes and with accuracy. The systems include a pump operating under the positive displacement principle. The pump includes at least one displacement piston, and at least one piston valve with a fluid slot, where the pistons in a cylinder define a pumping chamber. In general the displacement piston travels back and forth in the cylinder, producing suction, and discharging pumping action. The distance traveled by the displacement piston determines the dispensing volume of the pumping chamber and the direction of travel determines the direction of flow through any cylinder port. The piston valve rotates to align the fluid slot with a given cylinder port to communicate with the pumping chamber. 
     In refill mode, the piston valve rotates until the slot aligns with the intake port of the cylinder so the pumping chamber can communicate with the reservoir. The displacement piston retracts in the cylinder, expanding the pumping chamber, and drawing liquid from the reservoir though the intake port and into the pumping chamber. In dispense mode, the piston valve rotates closing the intake port so that the pumping chamber no longer communicates with the reservoir until the piston valve slot aligns with the discharge port out of the pumping chamber. The displacement piston slides forward, reducing the volume of the pumping chamber, expelling liquid through the discharge port. 
     In one embodiment, the piston valve includes a plurality of ports, such as an intake port, a discharge port, and a drawback port to permit precise delivery of liquids through a dispense nozzle without introducing contaminants, air bubbles, or liquid dripping. In drawback mode, in this embodiment, after the discharge step, the piston valve rotates closing the discharge port and the piston valve slot aligns with the drawback port, then the displacement piston slides back, expanding the volume of the pumping chamber, drawing liquid back in the dispense nozzle. The embodiment of the system also prevents contaminants and air bubbles from being introduced into the liquid to be dispensed from the nozzle by placing a filter across the discharge line downstream from the pump, and providing a separate drawback line for performing the drawback of the liquid in the dispensing nozzle so that drawback does not occur through the filter. This embodiment has special advantage in the precise control of semiconductor equipment used in dispensing liquid chemicals in ULSI technology. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective drawing of an embodiment of the pump, and illustrates the assembled pump including the pump module and the motor and base assembly. 
     FIG. 2 is a partial cross-section taken along A—A of FIG. 5 and a perspective drawing of an embodiment of the pump module. 
     FIG. 3 is an exploded view of the components of the pump module shown in FIG.  2 . 
     FIG. 4 is an exploded perspective view illustrating a preferred universal coupling for the piston valve. 
     FIG. 5 is an end view of the port fitting case, the valve bearing ball, the three ports of the port fitting case, and a clamp band around the port fitting case. 
     FIG. 6 is a schematic diagram illustrating the basic components of one embodiment of the precision liquid dispensing system. 
     FIG. 7 is an exploded perspective view with partial cross-sections of a ratchet-actuator assembly. The ratchet housing is on the left and the pneumatic actuator on the right. 
     FIG. 8 illustrates another view of the ratchet-actuator assembly of FIG.  7 . The pneumatic actuator now is on the left and the ratchet housing on the right. 
     FIG. 9 is a perspective view of the inner parts of the ratchet-actuator. 
     FIG. 10 is an exploded perspective view of the ratchet-actuator assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an embodiment of a pump  1  capable of transferring precise small volumes, e.g., 0-10 ml, of a liquid from a liquid reservoir to a dispense nozzle. The pump  1  can be used in a system such as that depicted in FIG. 6 to deliver resist and developer to semiconductor wafers. As shown in FIG. 6, the components of the system include a liquid supply reservoir  143 , a liquid supply line  144 , a three-port pump  1 , an upstream discharge line  148 , a filter  149 , a downstream discharge line  150 , a dispense line  151 , a dispense nozzle  152 , and a drawback line  147 . The liquid reservoir  143  can be a variety of well known reservoirs, the liquid lines are preferably of Teflon, the tube hardware and fittings can be Parker, Parabound Adaptor, Paraflare x Pipe BA-4F4, one suitable filter  149  is the Pall model no. MCD9116UFTEH, and the materials of the pump  1  will be described in detail below. 
     In operation, the pump  1  and the liquid lines are preferably charged with liquid. In dispensing mode, the pump  1  displaces liquid through the upstream discharge line  148 , the filter  149 , the downstream discharge line  150 , the dispense line  151 , and out of the dispense nozzle  152  onto the wafer. In drawback mode, occurring preferably a short time after the dispense mode, the three-port pump  1  valve is actuated to communicate with the drawback line  147  and the displacement piston in the cylinder of pump  1  reverses direction to enable drip-free dispense by drawing the liquid back inside the nozzle  152  through the drawback line  147  avoiding the need to reverse the flow through the filter  149 . This feature helps to prevent contaminants from being dislodged from the filter  149 . In purge mode, the system can use the drawback line  147  to prime any air out of the nozzle  152  also without going through the filter  149 . This feature reduces air bubbles from being introduced into the liquid dispensed. Alternatively, the pump  1  might add a fourth port to allow purge of air from entering into the liquid supply reservoir  143  through a liquid purge back line (not shown) to conserve resist. 
     Referring again to the embodiment shown in FIG. 1, the pump  1  includes a pump module, a motor and base assembly, and an electronic controller (not shown), and operates by the positive displacement principle. As shown in FIG. 2, the displacement piston  80  pumps the liquid by traveling back and forth in a cylinder liner  30 , as indicated by the arrows, producing suction and discharging action. The distance traveled by the displacement piston  80  in the cylinder liner  30  is proportional to the volume of the pumping chamber  87 . For liquid intake the piston valve  81  rotates so that the fluid slot  82  aligns with an intake port  85  (FIG. 5) so that the pumping chamber  87  communicates with the liquid reservoir  143  (FIG.  6 ). The displacement piston  80  retracts in the cylinder liner  30 , expanding the pumping chamber  87 , drawing liquid from the reservoir  143  (FIG. 6) though the intake port  85  (FIG. 5) and into the pumping chamber  87 . The piston valve  81  rotates closing the intake port  85  (FIG. 5) so that the pumping chamber  87  no longer communicates with the reservoir  143  (FIG.  6 ). 
     To discharge the liquid drawn into the pumping chamber  87 , the piston valve  81  rotates to align the fluid slot  82  with the discharge port  83 , and the displacement piston  80  extends into the cylinder liner  30 , expelling liquid from pumping chamber  87  through the discharge port  83 . To draw back liquid in the discharge line, the displacement piston  80  can retract immediately after the discharge step. However, in the preferred embodiment, the pump  1  draws back the liquid in the dispense nozzle  152  (FIG. 6) by rotating the piston valve  81  to align the fluid slot  82  with a drawback port  90 , and then retracting the displacement piston  80 . 
     FIG. 3 is an exploded view of the parts making up the pump module  10 . A valve bearing ball  96  is attached on a neck  35  (FIG. 1) of the piston valve  81  by a cone point socket set screw  161 . To form a liquid seal the pump module  10  preferably provides a cylinder end cap  160 , a Teflon thrust washer  158 , a flange  157  on the piston valve  81 , a Teflon thrust washer  163 , and a lip seal  162 . A conventional clamp band  43  is provided to hold a port fitting case  31  on the cylinder liner  30 . As shown in FIG. 1, a support  172 , preferably including a spacer  171 , is located under the port fitting case  31  to prevent rotation of the port fitting case  31  from torque produced by rotation of the motor  14 . The port fitting case  31  is preferably made of Teflon. Another liquid seal is provided by assembly of a cylinder end cap  79 , a lip seal  89 , and a cylinder liner  30 . A socket head cap screw  53  is provided which is inserted into a spherical bearing retainer  54  and a spherical bearing  75  with a race  154  (FIG. 2) and into the end of the displacement piston  80  to hold the retainer  54 , the bearing  75 , and the displacement piston  80  in fixed relationship with each other. 
     When the various parts shown in FIG. 3 are assembled, the pump module  10  appears as shown in FIG.  2 . FIG. 2 illustrates that the fluid seal includes a cylinder end cap  79  holding a lip seal  89  against the cylinder liner  30  and a contact surface  78  of the displacement piston  80 . FIG. 2 illustrates when the fluid slot  82  described earlier is aligned with the drawback port  90 . The clamp band  43  holds the port fitting case  31  to the cylinder liner  30  so that the drawback port  90  aligns with the L-shaped port  91  of the port fitting case  31 . Similarly, the clamp band  43  holds the port fitting case  31  to the cylinder liner  30  so that the discharge port  83  aligns with the L-shaped port  84 . The L-shaped port  91  narrows to a passage  92  in a male connector  94 , and threads  93  engage a twist tight collar  33  (FIG.  1 ). Likewise, the L-shaped port  84  narrows to a passage  99  of a male connector  101  and threads  100  engage a twist tight collar  32  (FIG.  1 ). Again, the fluid seal at the valve bearing ball  96  end preferably uses the parts discussed earlier in connection with FIG.  3 . The piston valve  81  includes a relief band  156 , which is slightly smaller in diameter than the rest of piston valve  81  to permit liquid to enter in the gap to prevent the curing of the liquid under the pressures and temperatures created by the tight fit and movement of the piston valve  81 . The piston valve  81  also includes an inner neck  159 , an outer neck  35  and is attached to the valve bearing ball  96  which has two slots  98  and  164  and a flat surface  97  for reasons discussed below. 
     FIG. 2 also shows that the spherical bearing  75  is held to a piston end cap  76  preferably made of stainless steel  316 . The piston end cap  76  is heat shrunk or glued on the end of the displacement piston  80  as shown in FIGS. 2-3. The displacement piston  80 , the piston valve  81 , and the cylinder liner  30  are preferably made of aluminum oxide or polished zirconia (YTZP) but can be also made of another suitable ceramic, a stainless steel, Delrin™, Tefzel™, or Kynar™. The advantage of aluminum oxide is it may not require lubrication beyond that provided by the liquid being dispensed or metered, it is extremely hard and resists abrasion, it exhibits little wear after many cycles, it is chemically stable, and it allows precision machining and diamond tooling with close running fits (100 millionths of an inch). Aluminum oxide&#39;s properties of low friction, hardness, and stability allow the pump module  10  to be primarily sealed by close clearance of the pistons  80 ,  81 , and the cylinder liner  30 . This means no compliant seals may be needed which eliminates a set of parts which frequently fail and require replacement in conventional pumps. 
     As shown in FIGS. 1-2, the pump  1  includes motors  14  and  22  for driving the pump module  10 . First, a stepper motor  22  drives the displacement piston  80  by rotating a bottom pulley  65  coupled by a drive belt  23  to a set of pulleys  24  and  64 . In alternative embodiments, the motor  22  can be a servo motor or another suitable positioning motor. The pulleys contact the drive belt  23  with sufficient friction and tension to prevent slippage between the pulleys and the belt. One suitable drive belt is the Breco-flex 10T5/390. A suitable pulley is the LS21T 5/20-2  made by Breco-flex. The tension of the drive belt  23  can be adjusted by loosening bolts  71 - 74  residing in the vertical slots of rigid plate  70  so that the pulley  65  can move up to reduce or down to increase the tension of the drive belt  23 . Thus, the rigid plate  70  provides an adjustable support structure for mounting the pulley  65  and the stepper motor  22 . 
     In a preferred embodiment if the stepper motor  22  rotates, the drive belt  23  transfers that force to the pulleys  24  and  64 , which rotate precision lead screws  44  and  19 . Eastern Air Devices, Inc., motor series LH2318 together with Intelligent Motion Systems, Inc. Model IM483 drive electronics provide a compatible motor and controller combination for this purpose. One end of precision lead screw  44  attaches to the pulley  24  and the other end rotates in a lead screw and linear shaft bearing block  29 . One end of precision lead screw  19  attaches to the pulley  64  and the other end rotates in a lead screw and linear shaft bearing block like block  29  but not shown to expose other parts to view. 
     Spacers  63  and  62  space pulleys  24  and  64  from triangular shaped lead nuts  58  and  25 . Lead nut  58  is fixed to a displacement slide block  46  by bolt  57  hidden by drive belt  23  in FIG. 1, a bolt  55  partially hidden by spacer  63  in FIG. 1, and a bolt  56 . The lead nut  25  is bolted to a displacement slide block  21  by bolt  61  hidden by the spacer  62 , a bolt  59 , and a bolt  60 . A pair of parallel linear bearing shafts  17  and  45  guides the displacement slide blocks  21  and  46 . A piston coupling  28  is attached by bolts  51  and  52  to the displacement slide blocks  21  and  46  and to the displacement piston  80  by the socket head cap screw  53 , the retainer  54 , and the bearing  75  described earlier. Thus, the piston coupling  28 , and the displacement slide blocks  21  and  46  move as a unit to drive the displacement piston  80  in and out of the cylinder liner  30  as the precision lead screws  44  and  19  rotate and engage the threads of the lead nut  58  and the lead nut  25 , respectively. Preferably, the displacement slide blocks  21  and  46  have holes, which are not threaded and therefore do not engage either the threads of the precision lead screw or bind the linear bearing shafts. 
     An adjustable flag  20  is held by bolts  49  and  50  to the displacement slide block  21  and overlaps an adjacent piston extended position sensor  15  when the displacement piston  80  fully extends into the cylinder liner  30 . Similarly, an adjustable flag  27  is held by bolts  47  and  48  to the displacement slide block  46  and overlaps an adjacent piston retracted position sensor  26  when the displacement piston  80  fully retracts in the cylinder liner  30 . One suitable sensor uses the Hall effect to detect when the metal flag interrupts a magnetic field emanating from the sensor. Another uses the photoelectric effect where an object fixed to the displacement block serves to partially or fully interrupt a light beam aimed at a photo detector. The Honeywell Microswitch 4AV series is suitable for performing this function. 
     FIGS. 1-2 illustrate that the pump  1  also includes a motor  14  for driving the piston valve  81  of the pump module  10  by rotating a pulley  38  coupled by a belt  13  to a pulley  12 . The pulleys  12  and  38  have sufficient friction with the belt  13  to avoid slippage. The motor  14  is preferably an air-powered rotary indexer because it quickly rotates the fluid slot  82  into alignment with a port when commanded by a conventional controller. In such a motor such as that manufactured by SMC, for example, the NCRBI-W30-1805 series motor, pneumatic air enters input  18  and a well known ratchet-gear mechanism converts the 180 degree movements of the motor  14  into the desired angular increment, e.g., 120 degrees for a three-port embodiment as shown in FIG.  1 . After an angular increment occurs the air is relieved at air exhaust  16 . In alternative embodiments, the motor  14  can be a servomotor or another suitable positioning motor. Preferably, a conventional controller using advanced solid-state electronics with microprocessor technology and sensors can be used to control the pump  1 , including the motors  22  and  14  to actuate the movement of the displacement piston  80  and the piston valve  81  at appropriate velocities, distances, and times. 
     FIG. 7 is a partially exploded cross-sectional view of an embodiment of the ratchet-actuator assembly  200 . The ratchet-actuator assembly  200  includes a ratchet housing  202 , a pneumatic actuator  204 , and an adapter ring  242 . The adapter ring  242  locates the pneumatic actuator  204  on the ratchet housing  202 . The assembly  200  is held together by socket cap screws  206 ,  208 , and  210  in the following manner. Screw  210 , for example, butts against a counterbore  220  in the ratchet housing  202 , travels through a ratchet hole  222 , then into a hole in an adapter ring  242 , and into a threaded hole  244  in the pneumatic actuator  204 . Screws  206  and  208  are similarly inserted and/or threaded through their respective holes in the same parts. In a preferred arrangement, the three screws  206 ,  208 , and  210  are spaced apart from each other 120 degrees. The screws  206 ,  208 , and  210  are held in the assembly  200  by internal threads in the pneumatic actuator  204 . Screws  206 ,  208 , and  210  use the leftover thread on the backside of cap screws  255  and  257  (FIG.  8 ). 
     Ratchet housing  202  houses a ratchet  234  integral or fixed to a ratchet shaft  214 . The shaft  214  has a groove  212 , functioning as a key seat. The ratchet  234 /shaft  214  rotate within the housing  202 , via a roller clutch/bearing assembly  218  press-fit into a collar  216  of the housing  202 . As shown in FIG. 8, the opposite end of the ratchet  234  has three teeth  223 ,  224 , and  225 , spaced 120 degrees apart from each other. The ratchet housing  202  includes a pawl  226  held to the ratchet housing  202  by a pin  227 . The pin  227  is fixed to the pawl  226 . Socket cap screws  232  and  235  shown in FIG. 10 hold a spring plunger block  230  to the ratchet housing  202 . The spring plunger block  230  laterally supports a spring plunger  228 , which biases the pawl  226  against a cam  240  as discussed below. 
     The pneumatic actuator  204  is a conventional pneumatic vane type actuator such as the SMC NCRB1BW30, including a vane blade  246  fixed and extending from a vane hub  249  attached or integral with a vane shaft  248 . A vane shaft collar  251  locates the vane shaft  248  axially in the pneumatic actuator  204 . A cam  240  preferably attached to the vane shaft  248  raises and lowers the pawl  226  off the ratchet  234  depending on the rotational position of the cam  240 . 
     FIG. 8 illustrates the same ratchet-actuator assembly  200  shown in FIG. 7, with a better view of the pneumatic actuator  204  and the internal parts of the ratchet housing  202 . In particular, FIG. 8 shows the end of the vane shaft  253  and the collar  251  holding the vane shaft  253 , the socket cap screws  255  and  257  holding the pneumatic actuator together, the location of port  18 , and the three ratchet teeth  223 ,  224 , and  225 . 
     Air pressure (e.g., 100 psi max) is applied through a conventional four-way solenoid valve (not shown) into the port  16  against the vane blade  246 . This rotates the vane blade  246  until it runs into a mechanical stop as shown in FIG. 8 in the pneumatic actuator  204  such that the lobe  241  of the cam  240  raises the pawl  226  off the ratchet  234 . This is the ratchet-gear actuator&#39;s normal pressurized state. When the air pressure switches into the port  18  and exhausts air through the port  16 , the vane blade  246  rotates forward as indicated by the arrow above the camshaft  238  shown in FIG.  8 . During this rotation the cam  240  lowers the pawl  226  back onto the ratchet  234 , which shortens the rotation of the vane shaft  248  from 180 degrees to 120 degrees when the pawl  226  engages one of the teeth  223 ,  224 , or  225 , spaced 120 degrees apart. Thus, as the ratchet  234  rotates, each ratchet tooth consecutively catches on the pawl  226 , which is swiveled axially about the pin  227  (shown FIGS.  8 - 10 ). 
     A roller clutch  259  such as a Torrington, type DC roller clutch transfers rotational motion from the cam  240  to the ratchet  234  (FIG.  8 ). The roller clutch  259  engages the camshaft  238  when the cam  240  and the camshaft  238  rotate forward as shown by arrow, which rotates the ratchet  234  in the same direction. During a reverse rotation, the roller clutch  259  disengages and acts as a bearing to the camshaft  238 , which allows the cam  240 , the camshaft  238 , and the vane shaft  248 , all fixed together, to rotate back to the normal position. To prevent reverse rotation on the ratchet  234 , a roller clutch/bearing assembly  218  such as Torrington, type DC roller clutch and bearing assembly, FCBL-8-K, is press-fit into the ratchet housing  202 , and acts on the ratchet shaft  214 . In a preferred embodiment, one alternation (i.e., forward rotation) of the pneumatic actuator shaft  248  produces one increment of direct rotation of the ratchet shaft  214 . 
     FIG. 9 is a perspective view of the inner parts of the ratchet-actuator assembly. It shows the vane shaft  248  having an end  253 , a hub  249 , and a vane blade  246 . It shows the cam  240  attached to the vane shaft  248 , and the lobe  241  at peak rotation to raise the pawl  226  around the pin  227  against the biasing force being applied by the spring plunger  228  at a contact point  231 . The plunger block  230  laterally holds the spring plunger  228  so that it can move up and down in response to the rotation of the cam  240 . A screw  201  is turned to adjust the amount of biasing force being applied to the pawl  226 . When the cam  240  raises the pawl  226 , the pawl  226  disengages from the ratchet tooth, here shown as tooth  224 . Rotation of the ratchet shaft  248  has the same affect with respect to the other teeth  223  and  225 . 
     FIG. 10 is an exploded view of the ratchet-actuator assembly  200  shown in FIGS. 7-9. The same parts shown in FIGS. 7-10 have the same part numbers. Roller clutch/bearing assembly  218  is shown before it is press-fit into ratchet housing  202 . The spring plunger block  230  is shown before a set of screws  232  and  235  are inserted in holes  221  and  233  of the spring plunger block  230 , and into the threaded holes  229  and  203  of the ratchet housing  202 . The ratchet housing  202  includes a notch to give access to the pawl and to secure the spring plunger block  230  to the ratchet housing  202 . FIG. 10 shows the ratchet  234 , the ratchet shaft  214  apart from the ratchet housing  202  and before the ratchet shaft  214  is inserted into the bearing  218 . The pin  227  fixed to the pawl  226  has two ends, including shown end  217 , both of which extend beyond the edges of the pawl  226 . FIG. 10 shows the camshaft  238  before insertion into the bearing  259  where the camshaft  238  contacts the inner bearing surface  258 . In this embodiment, the cam  240  is attached to the pneumatic actuator shaft  248  by socket cup point set screw  243 , being inserted into the camshaft  238 , and tightened against a flat surface  260  of the pneumatic actuator shaft  248 . The adapter ring  242  includes holes  245 ,  256 , and  262 , which correspond to the socket cap screws  206 ,  208 , and  210 , which in turn, are inserted into holes  268 ,  266 , and  270  in the pneumatic actuator  204 . An adapter ring dowel pin  247  is later force-fit in the adapter ring  242  and orients the ratchet housing  202 . 
     A suitable drive belt  13  is the Breco-flex 10T5/390 and one suitable pulley is the LS21T5/20-2 made by Breco-flex. The tension of the drive belt  13  can be easily adjusted by loosening bolts such as bolts  40 - 41  in the vertical slots at corners of a rigid plate  39  and moving the rigid plate  39  supporting the pulley  38  up to reduce the tension or down to increase the tension of the drive belt  13 . Thus, the rigid plate  39  provides an adjustable support structure for mounting the pulley  38  and the motor  14 . A L-shaped bracket  37  includes a conventional sealed bearing for supporting the shaft of the pulley  12  and an universal coupling  11  shown in FIG.  1 . 
     The universal coupling  11  eliminates the problem of how to exactly align the axis of the pulley  12  with that of the piston valve  81 . The location of the universal coupling  11  in the pump  1  is best shown in FIG. 1, but the details are in FIG.  4 . As shown in FIG. 4, an exploded view, the universal coupling  11  includes a coupling body  8  with a receptacle for the valve bearing ball  96 , and a set of pins  2  and  9  to hold the valve bearing ball  96  in the receptacle. Pin  2  engages slot  98  and pin  9  engages slot  164  on valve bearing ball  96  to provide a positive rotational coupling. Thus, the pump module  10  is held by the universal coupling  11  on one end and by the piston coupling  28  on the other. This permits the pump module  10  to be quickly removed from the rest of the pump  1  for cleaning or autoclaving. For example, to remove the pump module  10 , one would remove piston coupling  28 , then pivot the pump module  10  approximately 90 degrees with respect to the operational axis on pins  2  and  9  to the dofted line position shown in FIG.  4 . When slots  98  and  164  are aligned perpendicular to coupling  8 , the pump module  10  can be removed. To assist in that removal, the flat surface  97  of the valve bearing ball  96  provides clearance to the button  5  in universal coupling  11  when the pump module  10  is pivoted 90 degrees. 
     A biasing means holds the valve bearing ball  96  in place during operation and includes a button  5  biased by a Belleville washer  6  (i.e., domed shaped for spring action) and held by a retainer washer  7 . To install the biasing means in the coupling body  8  the following steps are taken. The Belleville washer  6  is inserted in the retainer washer  7 , the button  5  is placed on the washer  6 , and preferably three dowel pins such as dowel pin  3  are partially inserted in holes 120 degrees apart to protrude in the coupling body  8  to guide the retainer washer  7  along corresponding slots  174 ,  176 , and  178 . When each pin hits the end of its slot, where a hole exists, the pin can be driven into the hole of the retainer washer  7 . Because of the tight fit and flared shape of the pins, this technique firmly attaches the retainer washer  7  in the coupling body  8 . A cone point set screw  4  travels through the larger top hole in coupling body  8  and engages in threaded hole  180  in the retainer washer  7 , acting to fix the coupling body  8  to the shaft of the pulley  12 . As shown in FIG. 1, conventional spacers (not shown) maintain pulleys  12  and  38  at an appropriate distance from respectively the L-shaped bracket  37  and the plate  39 . 
     FIG. 5 is a detail end view of one embodiment of a three-port case fitting  31 . It shows where the cross-section A—A is taken in the embodiment illustrated in FIG.  2  and can be understood in conjunction with embodiments illustrated in FIGS. 1-2. In those embodiments, the top port dedicated to a drawback line, includes a male connector  94  defining a passage  92  and having threads  93 . The bottom right port, almost completely hidden in FIG. 2, and dedicated to an intake line, includes a male connector  168  defining a passage  167  and with threads  169 . The bottom right port communicates with the fluid slot  82  by the port  85  represented by dotted lines. The bottom left port, dedicated to a discharge line, includes a male connector  101  defining a passage  99  and with threads  100 . FIG. 5 also illustrates an embodiment for the valve bearing ball  96  including the flat surface  97  as well as the slots  98  and  164  for engaging pins  2  and  9  of the universal coupling  11  as discussed earlier. 
     Any given port can function as an intake or a discharge liquid depending on whether the displacement piston  80  retracts or extends into the cylinder liner  30  after alignment. Further, the port fitting case  31  is not limited to three ports as illustrated but could be a plurality of ports depending on the application. Accordingly, the pump module  10  could have multiple outputs and/or multiple inputs and/or multiple drawbacks and/or purge lines. In addition, a pump  1  could have a plurality of pump modules  10  disposed in parallel each having a stepper motor  22  or driven by the same stepper motor  22  and each having their own piston valve  81  and motor  14  or driven by the same motor  14 . Of course, this permits the compact pumping of different liquid chemicals with isolation between the chemicals. The design of the piston valve  81  dispenses and meters liquid without any secondary mechanism such as check valves which allows for longer life, higher reliability, and greater accuracy.