*Need Your Ideas* on Mechanically Automating the Reciprocation of a Hydraulic Cylinder

[Sam Burris]

The Question:
-How would you go about automation the reciprocation of the hydraulic cylinder?
-How would you mechanically automate this system?

Context:
-I made a material piston pump that is powered with a hydraulic cylinder...
-The material pump needs to be on demand so I am using a variable flow pressure compensated piston pump to supply flow when needed.

Current Solution:
-I am currently using proximity sensors on either end of the stoke to sense when its time to switch direction
This will turn on or off a latching relay which powers a directional control solenoid valve.

The Problem:
-For the application this is a "fragile/ unreliable" control system (relay logic)
-And near impossible to diagnose when something is wrong (and I'm the one who designed it)
-Also the switching speed is slow (this is bad because the pump will stop for a second causing inconsistent pumping and hydraulic pressure spikes)

Question Recap:
-How would you go about automation the reciprocation of the hydraulic cylinder?
-How would you mechanically automate this system?


Thanks for any input.

-Sam

 

[zeusfaber]

This thing you're trying to make is called an "Engine"

Look at the way they did it on steam engines - you might look at fitting a small flywheel and modifying Stevenson Valve Gear. Alternatively, try using end stops on your ram to nudge a spool valve from one end of its travel to the other.

Adapting steam engine gear can be a bit fiddly with an incompressible working fluid and a single double-acting cylinder- you may find it's hard to get things restarted if the engine stops right at the end of the stroke. Nudging a spool valve from one extreme to the other is likely to give you some interesting pressure spike.

A.

 

[Compositepro]

Mechanical cranks are usually the best way to get reciprocating motion due to the natural sinusoidal velocity profile. Any instantaneous reversal of motion results in jerk, which can become severe as velocity increases.

 

[Sam Burris]

@zeusfaber I like the idea of the end stop valve...
How would you go about building this? What parts are out there that might work that you are aware of?

As far as the rotary style actuators go, Its a good idea for the pressure curve but to get a big enough one to handle the torque and speed required it would use twice the flow rate of a cylinder and be way to large for the application.

Target Hydraulic PSI = 1500-2500psi
Material Pump Output flow = 100gpm = 50 strokes per min.
Material Pump Output PSI = 100psi = ~7000 ft.lbs. of force on shaft
Material Pump Stroke = 6in = 3in Crank Radius

ft.lbs. of torque = ft.lbs. @ 12in from center of rotation

3in = .24 of 12in
so
7000lbs/4(3in radius crank is .25 of 12in)= 1750 ft.lbs. of torque required for a rotary actuator.

If you continue to do so numbers a large enough rotary actuator to get the torque would be about 10-12 GPM

As the hydraulic cylinder will only take 4-5 GPM.

What I never mentioned is that this will be on a mobile trailer unit so yes rotary will work however when space and $$$ are a concern efficiency is key

Less efficiency = bigger engine, bigger more expensive hydraulic pump, bigger hydraulic res., more weight, more expensive motor vs less expensive cylinder and the list goes on.

 

[hydtools]

Use a pilot-operated directional valve. Take pilot signals from the cylinder as the piston passes a port and sends the pilot pressure to the directional valve. The valve can reverse the direction of the piston. Repeat.

Ted

 

[Sam Burris]

I like the sound of this...
@hydtools

What type of cylinder are you thinking?

The first thing that comes to my mind is...
Maybe using the concept of a cushioned cylinder but instead the cushioning port draining internally the port would go to a sequence valve.

and if the area of cushioning cone on the piston is less then the area of the other side
it would create a pressure multiplier enabling a sequence valve to work....

Another Thing I forgot to mention is that it is a double cylinder...

@hydtools
What type of cylinder are you thinking?

 

[BrianPetersen]

If you have electricity available (and you must, if you are using prox sensors and relays), ditch the relay circuit and use a simple PLC to operate a 3-position double-solenoid directional valve. Same sensors you've got now, probably the same valve you've got now, except now you'll have flexibility to program the PLC to do what you need it to do.

 

[Sam Burris]

use a simple PLC

Know of any water resistant/ outdoor rated PLC's?

 

[BrianPetersen]

It's as weather-resistant as the electrical box that you put it in.

 

[tygerdawg]

I vaguely recall that I have seen something like what you want, but it was done with pneumatics. Take a look at this guy's (Pete Vree's) pneumatics laboratory exercises on yoootooob. He has a beaucoup of really well done pneumatics tech lab exercises. Perhaps the logic of LAB14 given here can be applied in some way to your hydraulic system. You might need to dig around and find another that is a better fit.

https://www.youtube.com/watch?v=jNWR-FJ0cOE

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[hydtools]

Maybe a valve:

https://www.brevinifluidpower.ie/hy...tional-control/automatic-reciprocating-valves

Ted

 

[hydtools]

Or:

Ted

 

[73lafuite]

Hello,
If I had to do this, I would use a common mobile directional valve with an open center without a centering spring. And I would position 2 legs on the movable part of the cylinder which would reverse the movement at each end of the stroke by actuating the lever or the spool. Then with a little imagination you have to make a system with a spring hooked on the one hand to the lever and on the other hand to a rocker which will switch at each reversal