Research paper assignments should be perfectly edited and proofread. You should never allow your supervisor or instructor to proofread or edit your assignment, because it will do you no good. Yes, it is understood that out of going through research papers repeatedly there is a tendency of not noticing some conspicuous errors, but this is not a justification for presenting a research paper rich in errors. To overcome this, set your completed work a side for a day or two before editing. This will help you develop a fresh look at your assignment, hence noticing your mistakes. If this is not possible, draw in a different person to edit your work.