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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]
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]