Brad,
Question:  Is it possible to inhibit z actuator downward motion when
park cylinder switches are indicating not retracted?

Background:
Whenever the park cylinders are not retracted, the pump will be forced
to low pressure (hardwired by Kurt).  With maximum specimen weight and
no static support (blowers off), we will need low pressure set above
1000 psi to lift the load.  If we assume the load is balancing on two
park cylinders and all 4 z actuators get commanded down in low pressure
(say 1200 psi, can't get to high with park cylinders up), then the
maximum force on each of the two park cylinders is 76,000 lb.  Rated
capacity of cylinder locks is 50,000 lb, so locks would be overloaded.
This condition may never happen (load balanced on two cylinders,
operator commands z down), but it is possible.  If the z actuators can't
pull down with park cylinders up (S/W inhibit), then the maximu force on
each of two park cylinders due to the weight alone is 36000 lb, well
under capacity.  If we assume 3 park cylinders are supporting the weight
and all 4 z actuators get commanded down in low pressure, then the
maximum force on each of the two park cylinders is 50,700 lb, slightly
over capacity but still probably OK.  Manufacturer says overloads on
locks cause peening/yielding on rod which may have to be repaired at
some time.  Lock does not fail on overload and the rod does not buckle
at 76,000 lb.  Best solution is to prevent overload from happening.
Manufacturer does not have higher capacity locks.
During normal operation we will want to be able to command z actuators
up slightly to take the load off the park cylinder locks before release,
so we will need to be able to move up when park cylinder rods are
indicating not retracted.  So we can't have an overall motion inhibit
when park cylinders are not retracted.  Looking at not retracted signal
instead of locked signal prevents the z actuators from driving the park
cylinders down during their retraction which may intensify the oil and
overpressurize the park cylinders, valves, and tubing.

Yes, I know software engineers always have to bail out mechanical
engineers and their problems, but I ask for so little . . .

Jeff L.
