Swash plate pump, bottom of page.
http://www.pumpmarket.co.kr/tecinfo-principle.htm
The image shown is the reverse of what the pumps are like. Rather than the body spinning the plate spins. They may have something like a ball bearing riding on the plate pushing on the piston rod. On the other side of the piston they may have a spring to return the piston when the swash plate spins and reduces pressure on the bearing. If I find a better image I'll post it later.