How do I change the boom lift speed at the end of the operation using hydraulic cylinders and motor? 1

[Alex-1985]

Hello there!
I am designing a boom for load pickup, which also has to rotate. And one of the requirements is to reduce the speed of extension and rotation of the boom at the end of the ligting. What I mean by this. For the first 30 seconds, the boom has to lift at a speed of 0.3 m/s, and for the last 10 seconds, the lift speed has to be 0.03 m/s. I'm not very familiar with hydraulics, I'm just starting to learn it. So far I have realized that I need to use a hydraulic proportional valve and adjustable axial piston pump. I understand a little bit about l-s control when the pump changes pressure if the load on the boom changes. But I can't figure out how to forcibly change the boom extension speed when the boom load is unchanged. Could you please advise me in which direction to look and what equipment to pay attention to? And also how it can be organized.

Thank you!

 

[BrianPetersen]

I should add that my own hydraulics experience isn't with lifting booms but rather with hydraulic presses - and the desire to have a fast approach stroke and a slow, final, carefully controlled motion is also seen there. "How" that's done, covers the entire spectrum:

- Old fashioned manual handle-operated spring-centered directional valve with the flow coming from a fixed displacement hydraulic pump. The spool in the valve is designed to give you some control of how much fluid goes to the cylinder and how much bypasses, the further you move the handle the more it sends flow in that direction. There's another common application that works like this ... Old school farm tractors. (I grew up around those.) No electronics in the whole machine. These are always completely manual.
- Dual hydraulic pumps. Fast approach stroke from a big-displacement pump. Slow final stroke from a small-displacement pump that's in parallel - the big-displacement pump has a directional valve on its outlet that either sends flow into the pressure circuit, or it blocks the pressure circuit and dumps that flow back to tank.
- Dual hydraulic cylinders in parallel. Small-bore cylinder to move the tool quickly (but roughly) into position - during this motion, a check valve lets the main tonnage cylinder suck oil in from the tank. When you apply pressure supply to the main tonnage cylinder, that check valve closes and it applies pressure to the tonnage cylinder.
- And, of course, the fancy machines have proportional control valves and position feedback to a CNC controller.

The overhauling gravity load of the tooling requires consideration in the hydraulic circuit with all of these.

 

[FluidPowerUser]

Thanks Brian, that all makes sense.

Personally, I'm still not sure of the intent / purpose of the this website. It's nice to be able to guide others towards their goals and in the past I have tried to lead the OP to their goal by asking for more information and by giving some inputs here and there to get to the best solution. The trouble was, and I'm not suggesting that's case here, other people, with unhelpful and unqualified "advice", would derail the conversation with some bad anecdotal references.

All said, this website can only do so much. To safely and satisfactorily drive and control any machine requires deep knowledge and understanding of fluid power or electronics, also control theory as well. That equates to about $10,000 in course fees and 10,000 hours of empirical learning. On that basis, I try to keep it as simple as possible as most OP's state that they have limited knowledge and these things get awfully complicated very quickly.

I just looked at the description on the home page. It's described as a place for members to share and learn at the best source of peer-reviewed engineering information on the Internet. That sounds good, but anyone can be a member and who's to know what the right solution is?

 

[Alex-1985]

Thanks for all your replies!
It would be nice to have the big picture, but I have never designed such a system until now and I have lack of knowledge because this is a new field for me, and hard to understand all the requirements. Could you recommend YouTube videos, websites, or books where I could read more about how to design and develop such a system: how to choose a hydraulic pump, how and where to connect the pilot line, how to design such systems in general, and how to calculate them?

 

[FluidPowerUser]

Hi Alex

Is your "boom" entirely hypothetical? Could we possibly substitute "boom" with "swing" and convert linear motion to angular motion and still achieve your objective? Is your objective a learning objective or do you have a real application. Either one is fine, it just helps people to give the best answer.

So far, we have discussed a generalised approach to controlling linear displacement and the first derivative, velocity. People offering solutions will automatically think about the bigger picture.

A "boom" that is lightweight and moving light loads slowly will look and behave much more differently from a "boom" that has to lift 30 tons, work against gravity, lift people and mitigate against hose burst and also have flow sharing and priority flow control too.

In the modern context, moving a small and lightweight boom would be accomplished with a linear actuator. However, extending a boom on a tele-handler requires a different approach that is going to require a fluid power solution. The basic approach being something that is discussed earlier in this thread.

If you are set on a hydraulic boom, then you need to start with knowing the mass you want to move and how quickly you need to move it. This will tell you the power required. Pump selection is way down the list of requirements. There are a bunch of legal requirements and safety standards that need to be addressed before you need to decide on the type of pump.

Your opening comment at the top of the thread says that you want to design a boom to pick a load up and rotate it. Just doing these two operations will be subject to enormous changes depending on the load, the lifting point and the speed of the operation. It's all entirely possible and I am speaking from experience as I have designed machines and I currently design systems for all sorts of booms, from tele-handlers, to excavators, to crop sprayers, to access platforms and cherry pickers. With all due respect and you are right to ask for help, if you have no experience to draw from, why are your starting with such a challenging project as boom control? There are easier ways to start to learn.

YouTube is OK for general guidance and it's free. But that needs to be balanced with the fact that reference books are expensive for a reason and likewise, the courses are very expensive. As the Joker says...if you are good at something, never do it for free. Just search "Fluid Power Books" in a search engine and you'll get lots of options.

If you are in the UK, then you can get a good book from the BFPA for £9 and that has lots of good help. Likewise, the NFPA has information too, if you are US based.

If there are specific questions to ask, this forum can be helpful too.

 

[Alex-1985]

Thank you!

 

[PNachtwey]

All said, this website can only do so much. To safely and satisfactorily drive and control any machine requires deep knowledge and understanding of fluid power or electronics, also control theory as well.

Few in the hydraulic world have even figured out the control theory for controlling hydraulics. You won't find it in a book. Buy a hydraulic motion controller unless the system is very basic. A simple PI or PID control is not enough.

Personally, I'm still not sure of the intent / purpose of the this website

Me neither.
I/we have solutions but without info we can do nothing.
This isn't rocket science.

if you have no experience to draw from, why are your starting with such a challenging project as boom control? There are easier ways to start to learn.

Ditto.

It would be nice to have the big picture, but I have never designed such a system until now and I have lack of knowledge because this is a new field for me, and hard to understand all the requirements. Could you recommend YouTube videos, websites, or books where I could read more about how to design and develop such a system: how to choose a hydraulic pump, how and where to connect the pilot line, how to design such systems in general, and how to calculate them?

This is a huge learning curve unless the requirements are very small/simple.

As the Joker says...if you are good at something, never do it for free.

Yes!

Just search "Fluid Power Books" in a search engine and you'll get lots of options.

That won't be much help.
The fluid power books cover only the basics. The don't really get into motion control, just which way the actuator will move.
How do you calculate the natural frequency of a hydraulic motor and its load? You won't find that in book let alone what to do if the load moves away from the axis of rotation so its inertia increases.
What is the significance of natural frequency?

You don't find how to do this in a book.

https://deltamotion.com/solutions/pipe-handling-oil-gas

Honestly, I know it took the hydraulic and mechanical designers some trial and error to get it right.
We have our own labs. We design systems to be difficult and teach students how to control them. This a student controlling a load that goes over center so instead of pushing, it pulling once it goes over center. The gains/inertia are changing as the angle changes.
The swing arm is commanded in degrees, but this must be translated to linear positions, velocities and accelerations.

https://deltamotion.com/peter/Videos/Non-Linear-Lab_Medium.mp4

Peter Nachtwey
Delta Motion

http://www.deltamotion.com

http://forum.deltamotion.com/

IFPS Hall of Fame Member

 

[FluidPowerUser]

I have 36 years of experience on fluid power component and system design. To keep up with the modern methods and also because I'm interested, I had an intensive course on control of electro-hydraulic and mechatronic systems. That course gave a glimpse of PID control and opened up to Laplace, Nyquist, Bode, frequency response, phase margin, stability criterion. Etc. It's only when you try to write software to drive a machine, that you really see how these things work. The theory is in a book or on paper, actually doing it and making money from it is 10,000 hours of empirical learning. The suggestion is read a book, if you are still interested, then come back and seek more help.


All agreed. It's only when you have to create a model of the system and generate transfer functions for a valve, cylinder, hose, motor, fluid and so on, that you really get to understand the function of integrated systems. By function, I mean the way that system components respond to each other, before you even exert any sort of load on the system. Natural frequency and frequency response form the basis of the majority of systems.

It's only experience that really reinforces the dynamics of a mechanical system where the load is going over centre. The cylinder is pushing the load to start with, then the load is almost zero when the mass is vertical, before the load is then pulling the cylinder. The work done by the valve is constantly changing, so the gains have to change. It all changes again on the way back as the forces and flow to and from the cylinder are not the same for both directions of travel.

In this case, where the OP is asking about boom control, with limited knowledge of fluid power, it doesn't seem appropriate to ask if they have modelled the system as an LTI system to determine the phase margin or the number of poles. I tend to keep it more basic, still knowing that we can only achieve so much. Hence I am still wondering what the goal of this site is.

 

[Jacc]

Alex-1985, people are asking about the big picture. It is critical to understand your system so that we can help you.
You are not giving us any information at all which makes it hard to imagine what you are trying to achieve, a lot of guessing.

Here is some key questions, if you answer these we get closer to the "big picture":

How long is the boom? 5 feet? Or 50 feet?

How much will this machine lift? 100lbs? Or 100 ton?

Are the items being lifted sensitive? Are you lifting granite rocks? Or ceramic vases from the Ming dynasty?

Do you need to stop very accurately? Plus minus 1 mm? Or +/- 4 inches?

Will this machine be operated automatically from a PLC? Or will it be operated by a human pulling a lever?

Will this machine work 24/7 all year around? Or will it just operate once or twice a month?

 

[PNachtwey]

@FluidPowerUser. I have a YouTube channel called Peter Ponters PID. It is advanced and covers many topics not just hydraulics. You better be up on your Laplace transforms and differential equations. I cover motor, temperature, level control too.
I could teach control theory. I just happened to apply it to hydraulic motion because I was selling hydraulic motion controller.
There are many good books on hydraulics. Versma and Merrit are good, but they don't cover the control theory at all.
Jack Johnson has some good books that better cover hydraulic design for motion control.
I have many articles on the "Power and Motion", formerly "Hydraulics and Pneumatics", magazine but I don't go too much in to control but some articles have more info than those books I mentioned.

That course gave a glimpse of PID control and opened up to Laplace, Nyquist, Bode, frequency response, phase margin, stability criterion. Etc.

PIDs alone don't hack it for servo hydraulics. A glimpse is certainly not enough but that is probably all the instructors know. Teachers teach what they have been taught. Few have been in the trenches. I still see some teach "flow makes it go"

BTW, we have a forum that get gets more technical for Motion System Design.
This is a good thread.

https://forum.deltamotion.com/t/the-vccm-equation/378

Too many believe "flow makes it go" and that leads to many design errors.
We have the know-how, but we need info.
I think I have saved people more money by avoiding the mistakes than anything else when it comes to design.


Peter Nachtwey
Delta Motion

http://www.deltamotion.com

http://forum.deltamotion.com/

IFPS Hall of Fame Member

 

[FluidPowerUser]

Thanks Peter

The term “flow makes it go” boils my pee as it’s just not true and in the world we live in currently, too many people try to boil things down to make them less scary or less complicated. That does everyone a disservice.

I have access to many different controllers and software etc from my company. Thanks