We have had trouble with air somehow getting into our rams, even after bleeding the system several times. It seems as if air is somehow getting sucked into the rod seal on our low friction rams. We have had the sales rep and ram tech rep from parker take a look at the system, and they have suggested that we change the seals to standard type.
There is alos a fair amount of play in the spherical bearing on the rams rod eyes. This is not helping with the control system, and the combined play and air in the system is making tuning very difficult. We are hoping we can swap the bearing for higher tolerance types to reduce the play.
Once we have eliminated these issues, we will carry out further tests, but I fear it part of the problem is having a rotary encoder attached to the mechanism, instead of using transducer built into the rams, unfortunately we couldn't afford the latter. The only other thing we are going to try is to pre-load the ram with a spring acting against the push stroke, this should eliminate any play in the mechanism and bearings.