Lizzy, I'm sorry that I don't have much time today to look at this, but here's a quick analysis of your code:
1) you start by configuring the serial port - looks good
2) enter the sequence struture and send all three strings from the front panel controls to the serial port (from your description, it didn't seem like this is what you wanted to do). At the same time, you go into the event structure, but there are no events defined, so your program will hang at this point - obviously a problem here
3) if we pretend the event structure isn't present, you will go the the second frame of the sequence structure and enter the while loop - okay
4) in the while loop, you read the contents of the serial buffer (which, if the \r command stimulates a response, should contain something for the first iteration). You'll get a prompt for a file name from your write to spreadsheet file vi (but nothing is wired to it), and then the process will repeat as quickly as you can hit the cancel button in the file dialog (unless you never depressed the Forward DC motion start button, in which case the program will end). To end the program, you'll have to turn off the Forward DC.. button (which will be tricky with that file dialog popping up as quickly as possible)
So, it looks like you've got the right stuff in here, but not necessarily in the right order, or the best way. To keep things really simple, I'd use three frames in the sequence structure. The first frame would just send the \s command (and no event structure), the second frame will have your while loop, and the third frame will send the \b command. In the while loop, I'd just have a stop button to stop the acquisition (you don't need the forward and reverse buttons - the machine starts when you hit the run button on the vi) and a wait function to time the acquisition. Every iteration of the loop will send a \r command, and then look for a response on the serial port. Take the data and build an array using the shift registers. You can put the write to spreadsheet vi outside of the loop so it only executes at the end (when you click the stop button) assuming you don't run this program so long that it eats up all your memory. If Force and Displacement are coming in from the serial port, you can use a waveform chart to plot them both versus time. If you need to plot Force vs. Displacement, you will have to get a little more creative, but it really depends on what the data coming in is.
Sorry, I don't have more time right now, and I can't post code in 6.1. Work on it for a little while and post back. I might be able to help more later. Hopefully I understood what you were trying to do.
Chris
