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The challenge 

The challenge was to design High Throughput Screening System based on functional descriptions supplied by the  customer. The system was based on a simpler prototype model developed previously for the customer by DSA.  The first generation prototype system used only two axes of motion to move a target plate below a Sono-Tek  spray nozzle. The spray from the nozzle was directed by nitrogen gas directed by a proprietary design gas  distributor plate. The gas flow was controlled by an Aalborg gas mass flow meter. 

The customer wanted to take the next step and upgrade the capability of the basic system into an OEM  instrument. They contracted Data Science Automation, Inc. to perform the feasibility study and prototype system  design. The desire was to add motion to the nozzle to allow fine tuning of the spraying process. This motion  would be in addition to the motion of the targets on the X, Y stage. 

Additional enhancements to the system were desired in regards to the fluid delivery system that supplies the  sample fluid to the nozzle. In the original design a simple syringe pump and controller were used to deliver the  sample fluid to the nozzle. The new solution would need the capability to deliver a constant no-pulse stream of  fluid. To make the instrument even more capable it was desired to use a multi-stream selection valve to allow the  user to run up to 6 different fluids in the system. 

The final design specification called for the control of six axes of motion as specified by the customer and control  of the fluid and gas delivery systems. In order to leverage the knowledge gained on the previous system the  customer elected to use some of the same hardware. 

The Solution 

DSA leveraged National Instruments hardware and selected the PCI-7356 Six-Axis  motion controller. The Primatics motor drive was selected for its ease of integration with the NI motion control cards. No Universal Motion Interface is needed to connect the NI Motion card with the drive.  Both the PCI-7356 and the MDC800 allow the user to control stepper motors as well as servo motors. Using the  MDC 800 and the PCI-7356 reduced the number of hardware control pieces required for the system and helped  to reduce the size of the final instrument. 

The six axes of motion control are broken into 3 separate stages. The first controls the position of the target well  plate. This is a simple XY linear stage comprised of Parker/Daedel 404XE linear stages with LV233 stepper  motors. During the spraying operation this is the only stage that provides motion. The second stage controls the  position of the spray nozzle. It is comprised of a Y, Z, and Rotary stage. The Y, Z stage is pinned just like the XY  stage, but it mounted on a cross-member in the system above the XY stage. The rotary stage is a simple Apex  Dynamics gearbox mounted using a simple bracket. The gearbox controls the angle of the nozzle spray. 

DSA researched the available motors and stages including linear motor stages, rotary motion stages, servo  motors, and stepper motors. We helped the customer select the lowest cost robust option that would exceed their  motion requirements and allow ease of programming in the future. 

(??)The spray system will operate in several overall modes. First and foremost will be the spray mode. One of  the secondary modes is the wash mode. During the wash mode the nozzle is moved away from the spray area  and over a system drain. The nozzle is then rotated to point downward into the drain. 

The fluidics system was a new design that is completely different than the original prototype system. The original  system utilized a syringe pump and syringe pump controller. The new system utilizes multiple selector valves and  a continuous pump. The heart of the fluidics system was chosen for its unique ability to pump from 5-nL of fluid to  5-mL of fluid in a no pulse manner. Control of this valve is via a custom LabVIEW driver written by DSA. The  valve pump is connected to the PC via an RS-232 serial cable. 

DSA investigated multiple pump and valve technologies to determine which companies offered products that  satisfied the customer requirements, while at the same time keeping in mind that each piece of the system would  have to integrate with LabVIEW and National Instruments hardware. DSA was able to act as an informed agent  for the customer, utilizing our knowledge of systems integration. Utilizing DSA to do this research allowed the  customers scientists to concentrate on their core jobs and not have to take the time to learn about systems  integration. 

The valves in the fluidics system are manufactured by Rheodyne. They were selected based on their ability to  handle the pressure in the system as well was their ease of integration with the NI hardware. The first 6-position,  7-port valve has the fluid head exposed to the user of the system. This allows them to place the 6 inlet tubes into  sample or wash containers of their choice. The next valve is another 6-position, 7-port selector valve with four  ports blocked, allowing the valve to be used as a two-way diverter valve. The next valve is a 2-position, 6-port  unit that is used combination with the two-way diverter valve allow the user to alternate between loading the  sample loop and emptying out to the drain, or pushing the fluid through the system to the spray nozzle. 

Each of the valves has a built-in position control board and motor system powered by 24 VDC. Control of the 6- position valves is handled by what is described by Rheodyne as 4-channel Binary Coded Decimal logic. Four  input channels allow the user to select the position of the valve by sending the appropriate coded position logic  signals according to the following chart:

Table 1 - 6-position, 7-port Valve Position Control Logic 

The 2-position, 6-port valve is controlled by simple line logic. Position 1 is selected by sending a logic high signal  and position two is selected by sending a logic low signal. All of the valves in the system also communicate their  state of operation, either done or busy as well as communicating if an error has occurred during a commanded  move by setting the appropriate error feedback logic line to high. 

The spray nozzle completes the fluidics system. This hardware was used in the previous version of the system.  Sono-Tek provides a control box that allows the power of the ultrasonic atomizing signal to be controlled by  LabVIEW. The Broadband Ultrasonic Generator, or BUG, has two differential analog input channels. The first  channel is the external trigger channel that allows the user to turn the nozzle power on or off. The second  channel controls the power applied to the nozzle. The power channel is a 0-10 VDC signal, where 1 VDC  increment = a 2 Watt power increment at the nozzle. 

The vaporized spray is directed towards the target by the Nitrogen gas plate. The flow of Nitrogen gas is  controlled by an Aalborg Gas Mass Flow Controller. Control of this flow valve is through a differential 0-5VDC  analog signal. 

The final piece of equipment specified by the customer to be controlled by LabVIEW was an external HEPA filter  that attached to the spray box using a three-inch diameter hose. The Sentry Air System model 200 Floor Sentry  Hepa filter was selected based on its ability to provide low volume flow of 80 CFM or below. The Sentry Air  Systems HEPA filters are not designed for external control, so a random-on solid state relay will be used to turn  the exhaust fan on and off. The SSR control signal can range from 3-32 VDC.  

The following table details the channel mapping for the system IO and which hardware. The Analog signals are  connected to the PCI-6722 via the SCC-68. All the digital control for the valves is being handled by the general  purpose digital IO available on the motion control card. 

Table 2 – System IO Connections

 

Figure 1 – System Schematic 

Summary 

This application expands the functionality of a previous testing application and creates an OEM instrument based  upon National Instruments LabVIEW and NI Hardware. This system can be used to spray a multitude of target  items with ultrasonically vaporized liquids.