1756-HYD02 to be used with a saw.

I think there is some conflicting information on what the max speed of the cylinder needs to be. If you just look at the initial information which states 125mm/s max, then the flow required is only 84 L/min (see pdf attached). The parts that say 2 seconds in and out don't jive with that unless the stroke is very short.

1. mass of the load. aprox - 4 ton
2. the orientation of the hydraulic cylinder, angle - 30° Downward
3. the distance to move the load, (cylinder stroke) 16 "
4. the time to move out, 2 secs
5. time between moving, 5 secs
6. the time to move back in, 2 secs
7. the time to wait between cycles. tiempo entre ciclos. 15 secs
8. velocity and acceleration limits. 123 mm/s max no accel info

They have this proportional valve Rexroth 4WRKE 16 E1 125 L 3X 6E G24 E K31 A1 D3 M and they want to use it.
I do not know if that valve is suitable.

Valve web page: https://www.boschrexroth.com/en/us/p...es/4wrke/index

This is the data I got from cylinder dimensions.

Piston / Bore Diameter 4.75 in
Rod Diameter 2.5 in
Stroke 16 in
Pressure 1500 psi
Oil Flow 26.6218 gpm
Bore Side Rod Side
Area 17.7205 12.8118 in2
Volume 283.5287 204.9889 in3
Force 26580.8190 19217.7113 lbf
Time 2.7662 2 sec
Velocity 5.7839 8 in/s
Outflow 19.2473 36.8217 gpm
Ratio 1.3831

A real motion profile needs to be stated as the requirement and then a valve can be picked.

At Peter alluded to, valve rated flows are always for a specific pressure drop. In real applications, the pressure is changing. it is quite possible that you have a system with a valve rated 100L/min and you are using it at 180L/min or 50L/min. This is the hardest concept to get through when talking to people about proportional valves.

then throw the accumulator in there and for short periods of time you have more flow capability but then your pressure is not going to be constant as you deplete the accumulator oil.

@widelto, What does your ideal cycle look like. That is always the best basis for picking valves.
 
See attached files

@Peter
@Norm
After more than 3 years I went back to the plant and this is what I found :
They have disconnected the original Bang Bang Valves originally used for moving saw forward and back, now they used a proportional valve the same one I mentioned in post # 8 of this thread, they used a 1756-OF4 module to drive proportional valve to move the saw.
They have no feed back from saw cylinder position.
I asked them to send me a trend of this new situation, please see attached figures.
There is something I do not understand when the saw is moving forward (make a cut) they apply +3.2 V DC, when the saw is moving backward they apply -5.3 V dc, I would think that those values must be the same absolute value.
My guess that this is due to overlap.
I am going to try to use the valve they already bought, but my recommendation is to buy the one that Norm recommended.
You can see DC values applied to valve and the time they are using for cut and go back.
They use 2 secs to cut and 2 secs to return.

Proportional valve control.jpg Proportional Valve Trend.jpg
 
Widelto, hydraulic actuators tend to extend much faster than retracting as long as the pressure remains relatively constant. Therefore it takes a smaller control signal to extend than retract if going the same speeds.
The HYD02 has a method for compensating for the difference in open loop gains in each direction. That is part of the code I had to add when converting the M02AE code to HYD02 code back in the late 1990s.


The equation I used to compute the steady state velocities for hydraulic actuators is called the VCCM equation. The term VCCM stands for valve control of cylinder motion. The term was 'coined' by Jack Johnson.
There is a good discussion about the VCCM equation and why hydraulic actuators will tend to extend faster than retract with servo systems here:
https://forum.deltamotion.com/viewtopic.php?f=18&t=497
I start writing about the VCCM equation and Norm submits an example problems that we work out together. Anybody designing hydraulic servo systems should read this.
 
@Peter:
Having said so , Today I will present my proposal to that company .
I hope they buy and have all the equipment before ending january.
The only thing I do not like is that they are still stuck on Rslogix 5k V19.
I have V30 ,I will need to install V19, they have an old processor 1756-L61.
 
Widelto, hydraulic actuators tend to extend much faster than retracting as long as the pressure remains relatively constant. Therefore it takes a smaller control signal to extend than retract if going the same speeds.
The HYD02 has a method for compensating for the difference in open loop gains in each direction. That is part of the code I had to add when converting the M02AE code to HYD02 code back in the late 1990s.


The equation I used to compute the steady state velocities for hydraulic actuators is called the VCCM equation. The term VCCM stands for valve control of cylinder motion. The term was 'coined' by Jack Johnson.
There is a good discussion about the VCCM equation and why hydraulic actuators will tend to extend faster than retract with servo systems here:
https://forum.deltamotion.com/viewtopic.php?f=18&t=497
I start writing about the VCCM equation and Norm submits an example problems that we work out together. Anybody designing hydraulic servo systems should read this.

A couple of other things that can play into different signals required for the same speed in different directions are gravity and the fact that spool overlaps are not perfectly symmetrical due to machining tolerances.

I believe you said that the saw axis is at some angle from horizontal. In this case the force of the load, Fl is changing for different directions of motion.

Good luck
 
@Norm:
Yes, that makes sense.
Now I am reading info about the valve you recommended and comparing it to the one they already have.
I will meet valve salesman next week.
In case of any doubt , Can I have your attention ??
 

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