velocity - hydraulic motion

I want to do a hydraulic motion and i need to command a proportional valve from analog output 0-10V from PLC. The measurement of position is made with an encoder.

I need help. I am beginer in hydraulic motion.

I want to know how to calculate velocity with acceleration and deceleration ramp without jerk for obtain maxim speed and short time?

hecttorr said:

I want to do a hydraulic motion and i need to command a proportional valve from analog output 0-10V from PLC. The measurement of position is made with an encoder.

I need help. I am beginer in hydraulic motion.

I want to know how to calculate velocity with acceleration and deceleration ramp without jerk for obtain maxim speed and short time?

Click to expand...

you want control valve with push botton or varible ?

You don't have to calculate the velocity, if you use a pressure compensate flow valve. Or use a feedback to your analog output.

In my opinion, it is inpossible to calulate the velocity, as there are to many things what matters.

Jack

Go to http://www.deltamotion.com/, Peter has a lot of good info about hidraulic motion cotroller.

I need help. I need to calculate analog output signal to command a proportional valve. This signal must be proportional with velocity.

from Reuter: control valve is varible with acceleration and deceleration ramp.

One would implement a PID control system.

Search your help documentation of the controller for more info. Or use google!

You could calculate a loading profile, but you'd be crazy to if this is only a beginner level project.

Honga said:

One would implement a PID control system.

Search your help documentation of the controller for more info. Or use google!

You could calculate a loading profile, but you'd be crazy to if this is only a beginner level project.

Click to expand...

I agree, just use a PID so you're using feedback from the machine you like to controle.
There is no other way in my opinion.
If you want to calculate the velocity of your oil, you have to know the velocity at a fixed temperature, and you have to know how many heat is put into the oil while using it, and how many it's cooling during the process, and there are some things like the life-time of you're oil.
You need also to know the exact position of the plunger in your valve, this gives you also feedback.

What kind of hydraulic motion do you have?

Jack

As a beginner you would be wise to use a purpose built motion controller such as those available from Bosch Rexroth or Delta.

They are made to address the issues that arise from trying to do motion control with hydraulics.

More importantly, do you know anything about selecting the proper valve, cylinder and feedback device? How about the way the machine is mechanically designed. If you get these things wrong, you may not get the motion you desire with any type of control.

I hate threads like this. The questions are too big or vague. The OP asks a one or two line question expecting a book to be written in reply.

I always start with: "I need to move how much mass how far in how much time".

Hecttorr seems to be obsessed with knowing how to write the motion profile generator but as Norm pointed out the hydraulic design must be right first.

As a beginner Hecttorr should get some training or find someone that has experience at doing similar applications what ever that is.

OK, Hecttorr asked for it. Here is a 3rd order motion generator.
http://www.deltamotion.com/peter/Maxima/Seg1234567.html
Now what? Are you going to write that in a PLC?

I did not give many details about my motion. Sorry.

I need to move a cart with a mass 0,25 tons , on a distance 1 metter, time is 0,6 secounds.

For begin I want to use these equations in the PLC:

1 for acceleration
velocity_valve = ( encoder distance / acceleration distance )* velocity_target;

2 for maximum velocity:
velocity_valve = velocity_target;

3 for deceleration:
velocity_valve = [ (distance target - encoder distance) / deceleration distance]* velocity_target;

where:

*data input - acceleration distance, deceleration distance, distance target and velocity target are taken from HMI.
- encoder distance is current distance taken from the encoder device.

*data output - velocity_valve

The analog output signal is given by velocity_valve
The analog output signal 0-10V command proportion valve.

I have attached a image with velocity graphic.

I am open to any opinions and any advices.

hecttorr,

Have you calculated the acceleration or maximum velocity? You are in the 1.25g acceleration range and getting close to 100 in/s for the max velocity.

Is this a real project or just an exercise? If it is a real project you will need a motion controller (and a cylinder bigger than you would think with low friction seals, and a great feedback, and a good valve, and help ...)

If this is just an exercise then party on!

The cart is not caught directly from the cylinder. The cart is moved by a lever
and the mass of 0.25 tons is approximated with addition, probably the real mass is 0.15 tons.

hecttorr said:

The cart is not caught directly from the cylinder. The cart is moved by a lever.

Click to expand...

So why do you need the hydraulics?

Perhaps you should make a sketch...

The cylinder move the cart by lever.

hecttorr said:

I am open to any opinions and any advices.

Click to expand...

You will not accomplish this in a PLC. If it can be done at all it will be with a dedicated motion controller.

BUT
Unfortunately we still do not know enough to even begin. We actually know less because you never mentioned the lever before. The lever arm adds complexity, and more importantly, reduces the stiffness of the system.

Perhaps you should make a sketch...and post it

Click to expand...