# Hydraulic Ram Position System Ideas ?

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#### Neil Firmin

I need to replace a relay logic control system for a hydraulic walking foot
mechanism to a PLC based system. The walking foot is used to reposition a
conveyor head end unit. Seven hydraulic cylinders are used having a 500
mm stroke and a 200 mm diameter moving member. The control system needs to
know the stroke position of each cylinder in order to coordinate the walking
action. At present this is accomplished by using a set of switches on a cam
shaft. The cam/switch arrangement is fixed to the stationary end of the
cylinder and a pull wire attached to the moving end. When the cylinder
moves, the wire turns the cam which in turn operates the switches. The
working environment is extremely harsh with cylinders and switches normally
covered in mud, sand and water. I do not want to use the switch/wire
arrangement again as existing units are excessively corroded and prefer to
use a non contact sensing topology. I have spoken with a hydraulic company
with the view to fitting a linear type transducer inside each cylinder but a
retro fit is not an option on these types of cylinders hence I will have to
go external. The cylinders move relatively slowly and I have been
considering the use of low frequency ultrasonic transducers with sample
rates of 4 times/sec. Is there anyone out there who has been in a similar
position and is willing to share their experience?

Neil Firmin
Yallourn Energy Pty Ltd
[email protected]

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#### Pierre Desrochers

Neil - We have done a similar application twice in the past. The
environment was acid sulphuric 5% splashing everywhere and plenty of
abrasive dust/mud particals. Here is how we did this with great success.
We mounted a linear displacement encoder at the end of 1inch stainless steel
cylinder. The SS wire from the linear encoder mechanism was run inside this
1 inch cylinder wich was attached side by side with the real hydraulic
cylinder. We put two mufflers at the cylinder's intakes so no dirt would
get
inside.

We feed this signal in a PLC (in fack there where 4 of those cylinders in
the same system) with a double zone compare function we could turn off the
hydraulic of the leading cylinder making it wait for the other ones to catch
up.

This system had 4000 pound hyd. with 8" cylinders.

Gene Wilkins

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#### Peter B Simons (Jones & Jones Engineerin

Is there any reason why the cyclinders can not be modified for position?

There are options.