I recently got an Android POS device with built in printer. They provided some .so library files and a sample/demo program. I had #Walter Flores here in the forum do up a wrapper for the library and it is printing very well - no problems.
It will all depend on how your printer is connected. My guess is that it is on a serial port in which case you might try the direct serial output. I am including a program that worked for me on my device without the library. The device has a serial port that I connected an external DataMax ticket printer to and it printed with no problems. If you device is connected directly (which I suspect it is) to a RS232 port then you would just need to find the name of the serial port to use it. Mine was /dev/ttyS2