Open Loop Batch Control

Hello again, and thank you for taking the time to view my blog. Batch control, what is it? When you think of a factory with a bunch of little robotic arms for example working on an assembly line doing the same job over and over again, this is what batch control is.

In order for me to demonstrate a batch control process, one of my college teachers (Hassan Saberi)  dug up an old robotic arm from deep within some dusty closet room to spark life back into it (Thank you Hassan).



What the robotic arm looked like before I started working on it

Unfortunately this robotic arm required a lot of work to function properly. It would leak air all over the place, the valve array had 2 malfunctioning switch valves in it, and the hoses would get tangled all the time. However with the help of another instrumentation student (Dave Bertin), his scrounging through storage cabinets would show me that the college had many salvageable pneumatic parts that could solve many potential problems with the robotic arms. Many little valve arrays were in bags, along with replacement seals, pneumatic cylinders, and even pneumatic pressure regulators were found, so what I decided to do was gather all valves to make a whole new set of switches for the arm. I also added a 3rd arm to the table to enhance the batch process.

The new valve array uses a desecrate switching process (meaning it has a basic set of on/off switching connection points all bundled up together) which will eventually be connected to a DAQ controller. With the help of some new 0.6 mm internal diameter polyurethane tube (polyurethane had to be used because it was more flexible then polyethylene tube) and used salvageable tube fittings from an old pneumatic controller, I was able to restore these robotic arms to a more professional display setup. Plus with an added bonus, I even made a whole new pneumatic hook up port on the back of the arm table to make it more portable afterwards.



What the robotic arms look like after I fixed them up

The next task was to design an interface that I can use to control these robotic arms. Thanks to my previous knowledge that I acquired in the Electronic Engineering Technology program, I was able to whip up a fast and simple testing interface using Hex FET technology. What I used was transistor models IRF9Z34NPBF (which is a P-Channel FET) to switch 24 volt logic using 5 volts or less, and a bunch of 3904’s to shift the switching polarization to positive rather than negative switching then plugged it into a basic NI USB DAQ.

Because the valve array requires higher voltages to operate then what a USB
Port of a computer can offer, this switching interface allows this to happen
by using 5 volts to switch 24 volt logic

Now we get into the good stuff, building the batch control interface program. For this project, I used LabVIEW 2010 to make a quick interface which can be used to demonstrate what someone at a control console would see if they were tasked to monitoring a factories instrumentation. The program has both a manual control and an automatic setting which follows a set of step functions written in an initialization file (a *.ini file) for easy accessibility.

This is what a control console would look like when designed with
LabVIEW 2010

This is what a program made with LabVIEW 2010 actually looks like
close up.

So why is it called “Open Loop” batch control? Well it’s really quite simple; this robotic arm doesn’t have any sensors what so ever to report any kind of data back to the computer. The program does everything on a time coordinated sequence (and yes that also means if any of the arms didn’t operate the way it should in the second that the step sequence was switched, it would screw up the sequence that makes the block of wood move from arm to arm) which is called a sequence controller. A closed loop batch control would have sensors to report what each state cylinder is in since they are duel acting cylinders (that means you require air pressure to extend and air pressure to retract, single acting would have a spring so you only require one air pressure feed). This would allow an automatic waiting period so that each step will complete the way it should before entering the next step sequence.