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frans (Mechanical) (OP)
26 May 05 6:03
Does anybody in the forum have experience with hydraulic circuit design software. I would like to simulate operating conditions in complex circuits and get results such as flow losses, pressures and temperatures.
CanuckMiner (Mechanical)
26 May 05 8:18
I suggest having a look at Automation Studio.  I haven't tried it, but I've come across their literature, and it looks impressive.  It might do what you want.

http://www.automationstudio.com/

Cheers,
CanuckMiner
kcj (Mechanical)
26 May 05 9:18
I have been looking also.

Last time we looked, Automation Studio did great animation, schematics, training and color coding,motions, flows and steady state pressure drops, but NOT dynamic analysis of accel, decel, shock, etc.
That's what I really was looking for, so have not n\yet found something. There are several highly analytical dynamic programs, but beyond my level.

kcj
budt (Industrial)
26 May 05 10:45
Try this site for Easy5 software. If you have deep pockets it is supposed to tell all about everything just like a running circuit.

http://www.mscsoftware.com/products/products_detail.cfm?PI=414

I have not used it so I cannot say first hand how good it is.

Delta Computer Systems does some modelling of motion control circuits but I don't think it is a for sale program. You can check with Peter Nachtway at this site.

http://www.deltacompsys.com/

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

frans (Mechanical) (OP)
26 May 05 17:52
I have emailed automation studio twice in the past week requesting prices but not received a reply yet. Any idea on pricing of Easy5?
budt (Industrial)
26 May 05 19:42
When I first heard about it 10 years ago it seems the price was over $8,000.00. That was the reason for the reference to deep pockets. Even Automation Studio is over $4.000.00 the best I remember. Automation Studio doesn't claim to be true simulation but does have some variables like setting pressure and flow controls.

Here is another place to look that has a whole list of Simulation software.

http://fluid.power.net/fpn/docs/software.php3

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

kcj (Mechanical)
31 May 05 10:07
Easy5 was part of Boeing at one time. It was $$$, but also had optional mechanical, electrical, heat transfer, etc. ec. modules that would do very valuable dynamic siimulations.
k
frans (Mechanical) (OP)
1 Jun 05 0:55
I have an online demo with Automation Studio coming up. Will keep you all posted.
Helpful Member!  danhelgerson (Industrial)
6 Jun 05 11:00
I received a quote from Automation Studio about a year ago.  The basic professional program was $1,900.  The Fluid Power package was $3,440.  They would like the customers to also come for training.  You probably already have this... http://www.automationstudio.com/

Dan Helgerson CFPS, AFPI, AJPP
www.cfpsos.com

Helpful Member!(3)  EdDanzer (Mechanical)
9 Jun 05 15:12
Mathworks has their Matlab and Simulink products that will do simulations similar to Easy5. http://www.mathworks.com/products/product_listing/index.html
Some what spendy though.
Helpful Member!  PNachtwey (Electrical)
12 Jun 05 1:02
"Delta Computer Systems does some modelling of motion control circuits but I don't think it is a for sale program."

I do simulations for hydraulic servo systems and system integrators only.  What I have is not a product and not for sale.  However, we are looking into making a simulator for hydraulic servo systems available on the web.  We have found that too many people can not design hydraulic servo systems correctly.  It is no wonder.  There aren't any simple formulas for cylinder sizing.  The VCCM and natural frequency methods are incomplete and can lead to incorrect answers.  The only good way to do cylinder sizing is to use a simulator.  The down side is they cost money or require solving a system of differential equations.  

frans (Mechanical) (OP)
12 Jun 05 18:00
Actually I do not think there are too many people who can design a proper hydraulic circuit at all. I have up to now used so called hydraulic specialists working for the big hydraulics suppliers to do the hydraulics for my designs and boy more often tham not I have problems, ranging from overheating to functionality issues. It is as if these guys do not spend enough time thinking through all the potential issues - they are too keen to off-load components. The support afterwards is appalling. I have since realised that general knowledge is not enough and I need to be my own hydraulics specialist. A lot of what I do does not allow the luxury of fixing easily afterwards, so simulating it up front would be ideal.    
budt (Industrial)
12 Jun 05 18:38
frans wrote;

"Actually I do not think there are too many people who can design a proper hydraulic circuit at all."

You are not alone in your experiences. It is probably a lot more to do with Not knowing what is available, what causes heating, what is the best component that I sell, etc. than "Not thinking it through." If you decide to get the knowledge to design your own circuits you will be one of a rare breed in the industrial or mobile world of Fluid Power users.

Training in Fluid Power circuit design comes from manufacturers schools and is quick time at best. From that point on it is the College of Hard Knocks and OJT. Been there and done that.

Until industry decides they need trained, knowledgeable persons in house that have Fluid Power as their primary responsibility Fluid Power will stay the way it is. Anytime another way to perform the work normally handled by Fluid Power that way will be first choice. Electrical is always waiting in the wings to take over and they have the knowledge to do it. Lately I am seeing more jobs go to electrical power due to their constant upgrading and doing things that were unheard of even 10 years back.

Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us

frans (Mechanical) (OP)
12 Jun 05 20:42
I fully agree Bud. I actually try to use electrical whenever I can, but that does also tend to bind you to a few individuals who were involved with the design and programming and essentially the similar level of expertise needed. I used to argue that since I am not doing hydraulics every single day I am better off using someone living off the stuff - thinking they may know what is available and the individual characteristics of say a particular valve. I have done the training courses but as you say they are basic. The other day I asked so called experts at a training course to explain to me in clear terms where you would use what type of pump, gear vs vane etc - they do not know. Simple as that.

School of hard knocks I tell you - through poor design on my equipment I am learning fast! It does not come cheap though.
EdDanzer (Mechanical)
12 Jun 05 23:03
Very few collages offer hydraulic training so finding someone with formal training is difficult. My school of hard knocks has taught me to be wary of people in any industry. Having a good basic knowledge of any discipline you need to integrate into a product will cut your education costs. Reading trade publications, belonging to trade associations and getting quotes from several vendors can help define the direction to go with a project. I think there as many poorly qualified electronic people as fluid power people.
Unless you are doing very complex designs, modeling software can be overkill. Hydraulics is not any more complicated, than electrical, so a few good reference books can go a long way to checking quoted designs.
A rule of thumb that I tell people is there is no free lunch with hydraulics. Each motion function, and budget must be defined completely before choosing a pump and valve type. The greater the pressure and flow difference between functions the more difficult the problem.
PNachtwey (Electrical)
13 Jun 05 10:10
[tangent]
As far as I know the only college or university that teaches hydraulic is MSOE and Purdue.

Reading trade journals is not enough to learn the finer points.  I know because I have written several articles for H&P and the articles must be written to be more of a teaser.  One can't go into any topic too deeply with a 800 word limit and a minimum of formulas and examples.

I agree with EdDanzer's point about the number of unqualified electrical people.  I see electric servo designs that are sized in correctly so that the output from the controller saturates at 10 volts just like I see the same for hydraulic designs.
[/tangent]

I don't agree that hydraulics is not anymore complicated than electical.  One can find nice simple equations for resistors, inductors and capacitors.  Transistors and op-amps can provide gain that is very linear.  One can express the response many analog electrical ciruit using Laplace transforms.  Finally, I can buy precision parts so an electrical design will work as planned.

Hydraulics is non-linear.  Flow through a orifice or valve requires a square root function.  Hydraulic specifications are very loose.  One valve may be 10% different from another with the same part number. All of these factors makes hydraulic design harder and writing the simulators much more difficult and therefore more expensive.  It is hard to even find proper specifications that a simulator can use.  Too many assumptions must be made.
EdDanzer (Mechanical)
13 Jun 05 11:17
PNachtwey,
Your point about non-linearity is correct. I was making a general statement about simple applications either electrical or hydraulic. My experience with electric servo drives has never shown great linearity between motors and drives. Replacing either part usually requires retuning the system for stability.
I will suggest that if a drive system requires very precise control and low power electric drives are typically a better choice, partially because of closer tolerance components. For higher power drives hydraulics becomes the best choice up to about 400 hp, then electrics may become more viable.
The fluid power industry in general is resistant to change, and spends very little on R&D. My new company DEHydS ( dehyds.com), Digital Electro-Hydraulics Systems should change that. As with any new business, it is an uphill struggle to execute.
danhelgerson (Industrial)
13 Jun 05 15:18
This has been a very informative and frustrating string.  It seems clear from the comments as well as from some informal research that I have done that few people who actually need it are finding their way to the Fluid Power Society and the proper certifications that are available.  The people who are getting “Specialist” certifications are using it as a sales tool and not to truly promote the proper use of Fluid Power.  This is giving certification a poor recommendation.  Industry needs to have more qualified people on staff as a defense against the “Specialists” that are really only out to sell components.

Unfortunately, certification sometimes shows that a person knows how to study for an exam and not that they are actually competent to do the job.

I am a Certified Fluid Power Specialist and I take it seriously.   By definition, I am supposed to point clients to the best practices and the best use of Fluid Power, not to just sell a product.  That is one reason I started this forum.

Thank you for your comments and ideas.

Dan Helgerson CFPS, AFPI, AJPP
www.cfpsos.com

frans (Mechanical) (OP)
13 Jun 05 18:12
Sometimes hydraulics is simply more appropriate than electrics. One example I have is tunnel boring machines where I use electrical main drives where I can, but if prolonged operation at high torques are required over a wide range of speeds down to very low speeds, it does become a hydraulic system because of the time limitations on running a vector drive at low speeds and high torque - of course for a short period of time I can have comparitively far more torque with the electrical vector drive than with hydraulics. Technology advances all the time and maybe this will change. Also of course if you can keep the motor and drive components cool this becomes possible, but think underground robustness and reliability. Also often I work with 1000V systems - you try and find a 160kW 1000V vector type variable speed drive!

I do find that I can lay my hands on quite a few electrical control specialists who can put together a reliable and functional system with an acceptable commissioning problem level. I can not say the same for hydraulic systems sadly, and believe me, I have been through all the main suppliers in my area. That is why I now look to do my own hydraulic designs and I have been going through a process to gain the knowledge through the school for hard knocks.

First I started off studying the circuits I have been provided with and working out the suitability in my own mind. I found that I was often better at pointing out potential problems than my "experts"! But, I still lacked the practical nouse of what problems to anticipate where. Also, the appropriate design philosophy is still lacking a bit. I am learning though.     

kcj (Mechanical)
14 Jun 05 12:50
QQ  I found that I was often better at pointing out potential problems than my "experts"! But, I still lacked the practical nouse of what problems to anticipate where. Also, the appropriate design philosophy is still lacking a bit. QQ

This thread illustrates a problem my company is having: reliance on the outside experts as 'block box' solutions, without understanding it inside the company. I think the answer is a hybrid:  inside expertise to understand the application and potential pitfalls and problems as you noted, then combine that with the specialists knowledge of how to accomplishwhat we need to get done.

kcj
frans (Mechanical) (OP)
14 Jun 05 20:30
Unfortunately kcj, I don't think it work like that. I am an engineer with a masters degree and have been designing machines for as long as I can remember, so you can say I have a good grounding in just about all aspects of engineering. I understand hydraulic circuits. Unfortunately the devil is in the detail. Those "pitfalls" are things you only understand when you are intimitely involved with something. When you make a real study of it. If that is available in a book, please tell me tyhe title and my problem is solved. If not, you need the time to devote to the particular field of expertize not only theoretically, but you have to catch up with the practical day to day maintenance and problem solving to learn the nuances.
Helpful Member!  hydromech (Mechanical)
15 Jun 05 5:21
In my experience, the secret with hydraulic systems enginnering is to leave yourself room to change things. All too often designers...that's designers NOT hydraulic systems engineers, expect their designs to leap off the drawing board and start working...fat chance, it just doesn't work that way.

The mantra chanted by many many production managers all over the world is "more power, more speed". Too many hydraulically operated machines are installed,  commissioned and then abused by the customers.

Counteless times I have commissioned a system, trimmed it and got it working perfectly. 1 month later, the customers on the phone..."this machine dont work". I go back to machine to find the usual problems...compensators set above the system relief or the relief valve so high that stuffed the pump or split a manifold.

"Why have you done this?" I ask..."we wanted it to go faster" they say.

I always try to leave room for change...it is inevitably required.

My opinion on hydraulic design sofware is that it's O.K to a point. You feed information into assuming that all the information is correct...speeds...inertia...power available...torque etc. What happens if one of the paramaters is wrong? The software can't tell you. Everyone else will though...when the machine doesn't work.

All the software in the world cannot replace experiance. The best experiance is when things go wrong. Make a note of what happened and why and don't do it again.

Hydromech
Hydraulic Systems Engineer  
kcj (Mechanical)
15 Jun 05 10:03
frans:
I think we are saying the same thing. My point is that some managers (here but also at many other companies I know of) treat fluid power, and design in general, as a black box commodity that can be sourced from WalMart, kMart, or Target, whoever has the best price. As long as the project is defined in costs and schedules, the situation is 'managed' without understanding the nuances and details.

Experienced people are not respected because the outside expert has more aura and a better presentation of the latest technology. The major design decisions are frozen, the project comes back in house, and the people with the day to day engineering or operations knowledge are involved only in paperwork processing, until startup or support when it is too late to change key decisions. The old 'xx% of product life cycle costs are determined in the first 10% of decisions' or something.

I have a couple degrees, but mainly 30 years of learning and scars. Sounds similar to your background. My pipe dream, and what I was trying to say, is that all of that intimate knowledge of the details should be brought into a project early on. Use the outside vendors and experts who are up to date on the features of the latest product or technology in general. They are the people who may know better what 'can' be done. Add the experienced inside people who know what is the goal, what are we really trying to accomplish. That hybrid of closeup experience and wider view vision could be very efficient and productive.

kcj
PNachtwey (Electrical)
15 Jun 05 10:08
kcj, one of the biggest problems we have is getting the OEM to take ownership of the machines he is selling.  The OEMs claim they are too busy to watch what we are doing and then they need us back to help with the next machine. On top of that, they don't understand what is happening in the black boxes to explain how the system works to the end customer.  We do offer training courses for the motion control part.  Most companies do the right thing and send there people to be trained.  It is the other %10 that is a problem.

hydromech, I see the same problem all the time.  If the system is a sinusoidal test system, how much more power is required to increase the power by a factor of two?
Knowing the answer to this should keep people from trying to go faster than the designed speed.  Hydraulics can be fairly linear if the pressures inside the cylinder stay in the middle third of the pressure range.   Increasing the speed causes the pressures in the cylinder to swing out side of the this 'almost linear band' and the now the system is much harder to control.
frans (Mechanical) (OP)
15 Jun 05 16:35
Hydromech, why should I not expect a hydraulic system to work straight off, maybe with one or two adjustments? Relief pressures can be set beforehand. Flow regulators can be set before installation. If I spec the functional requirements to the satisfaction of the hydraulic designer he should be able to deliver a working system, or else it is either black art or he has not paid enough attention to detail.

I agree with allowing flexibility in designs. I agree the functional requirements has to be specified properly.

I do all this and I still get systems that do not work.
PNachtwey (Electrical)
15 Jun 05 23:59
"I do all this and I still get systems that do not work."

Why not?  If you have an data acquisition system you can see where your assumption were incorrect and learn to make better assumption or calculations. Data acquisition should be a new thread.

I have a system in the warehouse where I have position feedback and pressure sensors on all the ports of the servo valve.  I use this to verify my models.  I can acquire up to 16 data streams with 8 of those being external data at periods as short as .5 milliseconds.
frans (Mechanical) (OP)
16 Jun 05 0:05
Not all hydraulic systems uses data acquisition. It is nice if cost is not a problem, and I do have those, but not always. Secondly, how does that absolve hydraulic designers from coming up with proper designs in the first place?
PNachtwey (Electrical)
16 Jun 05 1:47
"Not all hydraulic systems uses data acquisition. It is nice if cost is not a problem, and I do have those, but not always."

The data acquistion tools are not part of any one particular project.  After you get the project installed then you take the data acquistion sensors and electronics with you.  This way you only pay for the sensors, AtoD converters and software once.

"Secondly, how does that absolve hydraulic designers from coming up with proper designs in the first place?"

I use my simulator.  As mentioned above, there are packages like the Automation Studio.  I saw the Automation Studio at the last IFPE in March.  I was impressed.  However, I don't think the simulations are as good as they should be, but I can see they are on the right track.   If Automation Studio can do what my simulator can do then it will be a must buy.  By the way, Automatin Studio can do many things my simulator can't do and it is a polished package whereas mine is not.

When I was at the IFPE show, I gave the specifications to my hydraulic system to the Fanuc ( the compay that sells Autmation Studio ) sales manager.  He quickly entered the data.  It took about 10-15 minutes.  When the simulation was started I could see the pressures, speed and velocity change.  However,  there was no way to see the values at any time in the simulation so I could not compare his results with my results.  It is this lack of quantitive data that keeps me from giving Automation Studio an unreserved must buy.
 

hydromech (Mechanical)
16 Jun 05 4:42
Frans...

Theoretical spec from a hydraulic systems engineer to a customer.

1. The power available to drive the hydraulic system will be infinite.

2. The noise emission might not be lower than 90 dBA.

3. The fluid used will be a standard 32 CST mineral oil.

4. All actuators will be located within 5 metres of the power unit.

5. All  of your inertia calculations will be accurate to within 1 mtr/sec/sec.

6. There will be no limits to the size of the pipework and the pipework installation will not be compromised and will not deviate from our requirements.

7. You will surrender the right to change any part of the  design of the machine once we have started to design the hydraulic system.

8. The fluid will be clean to ISO 4406 level 18/15/12.

9. Once the machine is commissioned by our engineers, all valve and pump adjustments will be sealed to prevent tampering by unqualified persons.

10. You will deal with third party warranty claims. If any part of the hydraulic system under performs due to efficiency problems caused by the hydraulic OEM's(pump or valve supplier)inability to publish accurate performance data we will not be liable.

11. We will charge you a fair agreeable amount for commissioning the system and training your staff on hydraulic systems maintenance.

Failure to comply with the above will void the warranty.


Lets face it Frans...this aint gunna happen.

In lots of cases the specification placed upon the hydraulic engineers requires a specific solution. That specific solution is shall we say..."the ideal".

The hydraulic engineers pass "the ideal"  system solution to the the customer or to the mechanical designers or to the electrical department.

Hydraulic systems engineers are a pragmatic collection of people, "the ideal" solution does consider every one else...it has to. Unfortunately, that concideration is not often reciprocated. The usual replies are "You can't put that there" or "that pipe will have to go around the machine" or " you cant have a motor that big...we haven't left enough room for you.

Already the hydraulic systems engineers are on the back foot...compromised...playing catch up and these are the known problems, they don't include cock ups and design failures.

Many many overall design failures manifest themselves in the performance of the hydraulic system. All the fingers point at the hydraulic systems engineers.

Frans...it should go right and it usually does. Hydraulic systems engineering is not a black art and my attention to detail is often offset other peoples lack of knowledge and experience.

Hydraulically operated machines cannot be delivered preset. I have seen brand new presses snapped clean in halve because some left a relief valve at a test pressure. I have seen the machining head on a brandnew boring machine fly clean off because the flow control valves was "preset"...fully open! It is best practice and basic common sense to shut all flow control valves and back off all relief valves to the lowest possible pressure bofore shipping the machine.

Hydraulc systems engineers : "Would you like us to commission the machine for you?"

Customer : "Nah it's O.K...I mean how difficlut can it be...it only turning a few knobs...isn't it?

1 month later...

Customer : "this machine wont work...there's something wrong with the hydraulics...we've had a got at it but its just getting worse...WARRANTY!"

Everyone has a different experience...this is just mine.      
frans (Mechanical) (OP)
16 Jun 05 5:57
You all make fair points. However, in my case the standard of expertise, design skill and professionalism offered by the hydraulics suppliers, and I have tried all the majors, who all offer to do the design for me, is not up to scratch. They want to sell components, they do not want to support or be held accountable. In general I do not find this with electrical control system suppliers. Or rather, I can easily pinpoint those indivicuals with the knowledge and skills to deliver what I need. Not with hydraulics.

Unlike the hydraulic suppliers I am accountable to my customers. Therefore I am moving to do my own designs or at very least being able to analyze what I am being offered. When i do mechanical machine design I calculate stresses and and strains and displacements and moments and forces etc, but I have never seen a hydraulics expert calculate in detail the flow losses, and heat build-up and dynamic response etc. Yes, I am a "it works and stay working after commissioning" type guy.  I fully accept there are individuals out there capable of doing so. Only I have never come accross them.

Patchey, I take your point on instrumentation and data acquisition. I gather you feel automation studio is not the final answer? Is the simulated data calculated, dispayed and then discarded - not stored in a file somewhere accessible?

Hydromech, I take your point on commissioning. See, I am learning.

hydromech (Mechanical)
16 Jun 05 6:24
Frans...

       You are right about the big OEM's.

       I have had experiences with all of them. Parker..Vickers...Rexroth...Denison. They are the same.

       At the front end the sales people...who generally don't know beans about what they are selling or how to correctly apply what they sell.

       Behind them are the product engineers...kept so far away from the customer...they couldn't give a toss.

       I have been working in the fluid power business for 17 years and every day is still a school day. If you ever hear anyone say they know everything about hydraulics...run away from them...they are dangerous.

       Lets not forget the name of this web site Eng-tips.com...this thread started as a question about design software and look where we are now...? I though the idea was to help each other out.

       There are lots of people out there giving hydraulic a bad name...I want to try and put a few things straight.

       If you need help...ask. Thats what we are here for. You will get an honset answers for free. There aren't many places that can offer that.
EdDanzer (Mechanical)
16 Jun 05 11:39
Depending on one manufacture to design and supply a complex system that will work flawlessly is not going to happen in any area, hydraulic, electric, electronic control, machining, fabrication, ect.
No one manufacture supplies best of breed in all hydraulic components, yet they will use marginal components to be sole supplier. I use components from both Sun and HydraForce even though they make products that do the same function. The reason is, each company has their own design for different valves and one may out perform the other is specific applications, the only way to find out is to test. If simple projects are failing, then the information given to the supplier must be suspect, not everyone can screw up every project.
We just went through a problem with a machine tool where the ladder logic and user interface would not work correctly or the same every time you pushed a button.
Simulation software will help, but if every detail is not set and followed, the results will be different. The size and in some cases changing the ID of a tube or the manufacture of the fitting or hose end will compromise the system. Long runs of pipe or hose can have ill effects. Then some problems are freak. I designed a system using a HydraForce CV08-21 check valve. The flow was high enough that the back pressure was a little to high, so I installed a CV10-20. This valve caused a malfunction. After much testing and instrumentation, we found the designs were different and the CV10 could float open during a pressure balance condition. Some things in life, are just learned the hard way, trial and error. No software could simulate these valves to determine if this condition existed as HydraForce didn’t know this could happen. Obtaining values for hydraulic valves would require testing valves constructed with minimum, average, and maximum tolerance, then using that range for simulation. The next problem would be hose, hose ends and fittings.
PNachtwey (Electrical)
16 Jun 05 18:56
"Obtaining values for hydraulic valves would require testing valves constructed with minimum, average, and maximum tolerance, then using that range for simulation. The next problem would be hose, hose ends and fittings."

We shouldn't have to do the testing though.  The manufacturers  should supply this data.  This is the biggest problem I see with simulators or even doing the calculations manually.  There isn't enough accruate data.

I want to know what the capacitance of pipe and hose is.  I want to know the equation for the spool area on a Bosch NG16 with a nic spool.  I want to know how to model the compensator on the pump.   Is the response of the compensator exponential or is it a combination of exponential and slew rate limited?  This information is not available.

Frans, Automation Studio looks close, but ready for use as a design tool yet.  Fanuc is pushing Automation Studio for class room or training purposes.   I will dust off an example of one my simulations.  I have a .pdf site where I can post it later.

  

PNachtwey (Electrical)
16 Jun 05 23:33
Here is my attempt at a simulator.
ftp://ftp.deltacompsys.com/public/PDF/Mathcad%20-%20Hydsim-ps.pdf

I, actually my customers, do a lot of hydraulic servo control. This is a Mathcad worksheet that I use to sanity check designs.  I can see how the pressures will change as a function of time.  I can also check to see if the actuator will accelerate and decelerate properly.  In this example the pressure graph on page 7 is most important.  I can see the pressures are getting close the system pressure and the blind end pressure is getting close to cavitating.  Also, notice the ringing at the end of motion.  This system is not very stiff.  This system did not work well.  It had to be re designed to use 3.25 in diameter cylinders to get the required stiffness.  This was for a flying shear and it must track within .010 inches.  If the cylinder is not stiff the 'slinky' effect can be greater than .010 inches.

This simulator is solving a system of differential equations  using iterations of increments of 125 microsecond.  I have more information on how the simulator works here.
ftp://ftp.deltacompsys.com/public/PDF/Mathcad%20-%20HydSim.pdf
It use a numerical integration technique call advanced Euler.  It is being rewritten to use Mathcad 12 and the Runge Kutta method.

The program is actually a little more sophisticated than the  documention says it is.  I have added pump flow and accumulator volume to the simulation.  What is neat is that I can try different things like running the piston to the end of the cylinder to see how the pressures change.  I can hang a mass veritically and see the actuator cavitate on the  cap side.
frans (Mechanical) (OP)
17 Jun 05 5:41
I agree fully with PNachtwey: "We shouldn't have to do the testing though.  The manufacturers  should supply this data.  This is the biggest problem I see with simulators or even doing the calculations manually.  There isn't enough accruate data."

Maybe one of you guys specializing in hydraulics should compile a standardized component information framework covering the test and specification information that should idealy be made available by components suppliers.

You may even be able to set up a site such as Tomshardware to compare different brands on standard tests and make money out of it.

Patchey, your simulation is impressive. Again, you may find a market if you add enough block components so users can build systems. I build complex spreadsheets for machine design because I know the stuff so well, but it would take me far too long to set up hydraulic simulations like you have done. Hence my search for something off the shelf - I do not develop my own FEA software for instance, even though I can do it from first principals! Used to do that years ago to be fair. Just too busy now.
Helpful Member!  HCMechSys (Mechanical)
19 Jun 05 13:31
Has anyone tried the free PCBathFP software for hydrualic circuit simulation?

I teach basic hydraulics and have gotten the students to use it to creat basic hydrualic circuit diagrams. I'm thinking of incorporating some basic simulations as well into the course. As someone previously posted, I believe simulation can only do some much before you have to build prototypes and try some experiments. But I thought an exposure to simulation is important as well.

Any thoughts on the software greatly appreciated. It can be downloaded from:
http://www.bath.ac.uk/mech-eng/ptmc/pc_bathfp/pc_bathfp.html

frans (Mechanical) (OP)
23 Jun 05 23:52
I tried it and it works well, but is limited in the components that are available. To get components added you have to contact the University and I can just imagine how long it will take our theoretical cousins to add just one component - so as a practical tool unfortunately I think of limited use.  
HCMechSys (Mechanical)
24 Jun 05 10:10
frans,

Yes, I've tried the "support" and its definitely not the fastest. But for a free tool, that's to be expected.

Have you tried the simulation capability? I've tried a simple example involving an unloaded hydraulic motor, pressure-compensated throttling valve and counterbalance valve and have had problems getting the results to agree with measurements from a corresponding circuit I put together using a Parker training station. The program seems to play with the volumetric and mechanical efficiencies and prevents me from adjusting things to get the results to agree. I've tried the "support" and they've never gotten back to me.

I was curious if this sort of thing is common with other tools like Easy5, Automation Studio, etc or is this a quirk of the BathFP program. Any thoughts or examples to try most welcome....
HCMechSys (Mechanical)
30 Jun 05 13:10
I thought it might be a useful exercise to try to run PNachtwey's servo-valve example using the PCBathFP software.

A summary of the simulation and comparison of results is at:

http://ca.geocities.com/hchesser@rogers.com/Ex-Eng-Tips.pdf

I found that the analysis basically confirmed what PNachtwey was saying the system is not stiff enough to drive the heavy load. However I found that the PCBathFP software did not let me set the initial conditions for the accumulator and line pressures so I was not able to replicate the simulation. I've e-mailed the Bath people to see what can be done. In the meantime, I think I've thought of a way of setting up the right initial conditions.

I did have a question about the initial line pressures - why were these particular equations/pressures chosen?
PNachtwey (Electrical)
30 Jun 05 21:47
Wow, nice effort.  Thanks.  I haven't had time to examine the BathFP software.
I think there are a number of things that make the two simulations different.

1. You should have used 35 bar instead of 70 part for rated flow for each land of the spool.  Notice my ValvePSID/2.

2. You used linear instead of cosine ramps.   Linear ramps have high frequency components that will induce oscillations.   Cosine ramps have only the one frequency component.

3. Some how you got the actuator to retract too far and back up against the cap end of the cylinder at 1.35 seconds.  The BathFP software does exactly what I would expect it to.   My simulation did not hit the end of the cylinder.

"I did have a question about the initial line pressures - why were these particular equations/pressures chosen?"

Are you are referring to Pa0 and Pb0?  If the initial velocity and acceleration are 0 then there must not be a net force on the piston.   Just to the right of where I set Pa0 and Pb0 is calculate the force on each side of the piston to make sure the force on both sides of the piston are equal.   I can also use this simulation to handle vertical loads.   In this case the load force on the rod will be non zero.

If you are referring to P0 ( pre-charge pressure ) or P1 ( system pressure ), the system pressure be high to keep the system as linear as possible for the motion controller.  The pre-charge pressure is high relative to most hydraulic systems.   I like to keep the system pressure as constant as possible to make tuning the motion controllers easy and reduce following errors.

HCMechSys, I think you should be able to fix items 1 and 3 fairly easily.  It would be nice to rerun the BathFP simulation.   I am also interested in the feedback you get from BathFP.   I will work on making my simulation metric friendly.
HCMechSys (Mechanical)
1 Jul 05 9:12
Thanks, I thought it was useful for me anyway.

1. Regarding the 35 bar vs. 70 bar - I saw your dp/2 equation but thought the software was asking for the full drop across the valve. I think you're right though...

2. Unfortunately the profile you can enter is limited to 10 steps, so I couldn't put in more points to fill in the cosine function a bit better. That is a fairly big limitation.

3. Yes because more of the flow is diverted to the accumulator early in the simulation and less at the end of the simulation, the cylinder manages to get back all the way to the cap end.

My question was referring to the Pa0 and Pb0 and yes I did notice that intially the forces are balanced. But what is the rationale behind the pressure values used? If we were running the machine with a relief valve setting of 2500 psi and lets say we had just retracted the cylinder, then I would expect 2500 in the rod side line and something less (2500Ab/Aa, I think) on the cap side...
PNachtwey (Electrical)
1 Jul 05 10:54
Actually, just about any set of pressures will do as long as the net force is zero.   I have found from research ( playing ) with my hydraulic system, that the pressure does not reach system pressure on the rod side while just holding position without a load.  In fact the steady state pressures will be different after an extend move and a retract move.  This means that a move from 10 to 20 inches after a move from 20 to 10 inches is different from a move from 2 to 10 inches, stop, and then move to 10 to 20 inches.
When I say different, I mean the pressures will be different.  The motion controller makes sure the net force and therefore the acceleration and velocities position the same.

My hydraulic system has pressure transducers on all the ports of the servo valve which is a Bosch NG10  -803.  I can monitor position and the pressures at .5 millisecond time intervals and record, save and display the data.  I can also use triggers to start the data acquistion like a logic analyzer.  These features are built into the motion controller.  I used these tools to gain knowledge of how a hydraulic servo system works.

ftp://ftp.deltacompsys.com/public/jpg/PA080005.JPG

I verified my model against my system.  It is close, but my hydraulic system is just one system.  I have been able to use my simulator to keep customers out of trouble by showing them the simulation of their design was not good.  Just like the example above.  I need to spend more time doing research ( play ). This is good stuff.

I/We make and sell hydraulic motion controllers.   I am interested in the physics of hydraulics and how to really control it.
HCMechSys (Mechanical)
8 Jul 05 16:14
Well I finally got around to modifying the BathFP analysis so that I could reflect the same initial conditions as the analysis in PNachtwey's post.

The updated inputs and outputs can be found at:

http://ca.geocities.com/hchesser@rogers.com/Ex-Eng-Tips2.pdf

Overall the results are much closer now than before. I suspect the only differences now are due to line sizes and minor things I didn't set properly in the BathFP objects.

PNachtwey, do you have measured results from your set-up (thanks for the picture of that by the way - nice equipment) to compare with this analysis? It would be interesting to see how close the analysis comes...

PNachtwey (Electrical)
8 Jul 05 19:45
That simulation was for a customer's system that didn't control very well.  I increased the size of the cylinder in the model until the motion was stable and the A and B port pressure were in the middle third between system pressure and 0.  They ended up with a 3.25 inch cylinder instead of the original 2.0.  They didn't like having to redo their system.

[detour]
I find that sizing cylinders if very tricky.  I don't trust any one set of equations.   The natrual frequency method and the VCCM method have flaws. Choose the maximum between the two will generally get good results.  However, I prefer the simualtions for the final word.  It is too bad that it takes so much effort to get a simulation set up.
[/detour]

I can get the data for my system, in the picture, and I have a simulation for it but that will have to wait till next week as I am going home time.  I will comment about HCMechSys's new simulation when I get home and have more time.

EdDanzer (Mechanical)
8 Jul 05 20:53
PNachtwey,
The picture of the test device brings up some comments that may affect stability of the system.
1.    The aluminum block that the valve is on will cause some volume variations if pressures run very high.
2.    The tube running to the rod end is probably too small and too thin of wall for optimum performance.
3.    The cylinder barrel wall is probably too thin for maximum performance.

Depending on the accuracy needed, back pressure caused by too small of plumbing to the cylinder ports can effect response time.
As the cylinder stroke becomes longer in relation to the bore, pressure expansion of the port tubes and the barrel will affect the stiffness of the system.
PNachtwey (Electrical)
11 Jul 05 17:13
EdDanzer,  except for the LVDT feedback being inoperable right  now my system in the picture is almost perfect.

ftp://ftp.deltacompsys.com/public/jpg/after%20tuning%20wizard%20bw%205pt1%20hz.png
ftp://ftp.deltacompsys.com/public/jpg/after%20tuning%20wizard%20bw%205pt1%20hz.plt

The links show how accurately I can move this system.  The position units are on thousandths of inches so 4000 is 4 inches.   Notice that the red line ( actual position ) covers the cyan line ( target position ).   This shows the system is perfectly tuned.  The lines are color coded.  I used my tuning wizard ( auto tuning ) to calculate the gains for the motion controller.
The .plt file is a text version that can be imported into Excel or Mathcad to plot the way you want.  This is how I do my research.  The time periods are really increments of 1/1024 seconds so 4 means 4/1024 seconds.  Notice also the sum of errors squared in the gray box.  It is only 435. This is the sum of the error at each timer period squared and
summed for the whole graph.  An error of 2 thousands would show as an error of 2 and add 4 to the sum of errors squared.   Some people call this the ISE or integrated squared error.  The goal is to minimize the ISE or sum of errors squared when tuning a system.

Ed,  the simulations in the previous post above are for a customers systems, not mine.  The links in this post above are for my system.

1.  The aluminum block has the connections for the pipe leading to the rod end.  It also has the P and T pressure sensors as well as the P and T ports.  How do you get rid of the block and still have all these ports?

2.  The pipe to the rod end look big compared to the ports.    How big can the be?  What choices do I have?

3.  The pressure that I am operating at is only 1500 PSI.  I doubt I am streching the cylinder in a noticeable way.  At least the motion controller doesn't seem to care.

The stiffness of the system will vary a lot depending where you are in the stroke.  The cylinder stretch does not affect this in any significant way.

ftp://ftp.deltacompsys.com/public/PDF/Mathcad%20-%20Natural%20Frequency.pdf

This is not for my system, I just want to assure you I know how to calculate natural frequency as a function of cylinder length.

I will get the HCMechSys data tonight hopefully.
PNachtwey (Electrical)
11 Jul 05 22:52
HCMechSys, your simulation look pretty close after you let the BathFP simulation reach a steady state condition before start the control sequence to the valve.  There are a lot of place where BathFP and I could make different assumptions that would cause the rest of the difference.   I think I do many more updates.  My simulation looks a lot more rounded than the BathFP simulations.  This could be cause I use 125 microsecond periods.   The BathFP periods could be a lot longer.

You are right to use the sqrt(35bar) for calculating the pressure drop.  If you go to the BoschRexroth website you will see the same thing.  I appreciate your efforts.   Are there any suggestions you have for me besides using SI units?
I know my simulation is not perfect.  I don't think any simulation will be.  I will try to show a simulation of my almost perfect hydraulic system.

EdDanzer,  where would I get the capacitance of the cylinder or pipe.  I don't see this number published anywhere.


HCMechSys (Mechanical)
12 Jul 05 9:40
PNachtwey,

I looked at your previous posts and see that you are thinking of making this into a web-based tool. I like that as an idea - here are my thoughts as to how to go:

- on the technical side, I do think you should explore the parameter space of the model to see what are its limitations in terms of system pressure, flowrates, command signals, etc. This is where "playing" with the system you have would come in very handy. This would provide valuable advice to your users as to valid input parameter ranges.
- also, I would check your results against other software tools especially for parameter ranges not easily tested with your system. This is after all why one turns to simulation - to see what system changes produce better/faster performance without having to physically experiment - of course there are limitations to that as many have already noted above.
- the code itself can only analyze the behaviour of the valve-controlled cylinder, which of course is a very common circuit - but on the other hand it would be nice to be able to plug and play with components to make your own circuit - that's where tools like Automation Studio and BathFP are kind of nice
- one thought I had (since I've been "playing" with equipment at the college where I work) is that it would be handy to be able to tune the system parameters to match measured results - a sort of system ID tool, not sure what's out there that does that now - anyone?
- I assume the intention is to add a browser-based GUI, which sounds like "fun" (depending on your definition of course)

I'll look up that Bosch Rexroth valve and see what catalog data they have - hmm - this may be an "excellent" (again depending on your prespective) test question for my students actually....
PNachtwey (Electrical)
12 Jul 05 10:44
I was thinking of a Java applet.  The trick is to get enough detail to make the simulation accurate enough with out making the simulation to difficult to setup with too many parameters.  For instance, EdDanzer suggested the cylinder expands.  Yes, it does.  This has been mentioned to me before at the last IFPE show is Las Vegas.  If I have a typical default valu, I would use it.  This way a user could just use the default value unless he knows a better value.  I am even more interested in the capacitance of pipe and hose because the capacitance of the hose and pipe is so much higher than the cylinder.  I don't see capacitance ratings for those item either.  How is one suppose to design a decent system without knowing all the facts?

-I would only simulate servo valve controlled cylinders.   That is all I am interested in and simulating counter balance valves, sequence valves etc is just more parts that must be modeled.

-The graph of the motion of my system above used my auto tuning algorithm.   I can ID systems as a gain and a time constant or a gain and a damping factor and natural frequency.   This is good enough for auto tuning.  I can then select the desired bandwidth and the tuning software will select either an overdamped or critically damped response that will achieve the desired bandwidth.

Where do you teach?
HCMechSys (Mechanical)
12 Jul 05 13:09
PNachtwey,

I believe the capacitance of the hydrualic line is related to the stiffness of the line - just as an electrical capacitor stores charge/voltage, the hydraulic line stores pressure by expanding (like your cylinder). The line stiffness is related to the material (as well as diameter and wall thickness) of the pipe in question. This is basic pressure vessel stuff - I'll see if I can find a readily available reference for you on this. If the line has significant bends, etc then it gets more complicated. But for a basic tool a simple model should be sufficient as a starting point anyway.

For your GUI, you could have a range of picks for line models - like Schedule 40 steel pipe, SAE 100R, etc. Maybe as a first cut, you could also offer a "rigid line" or "ignore line capacitance effects" pick.

I agree that from a control systems standpoint the circuit can be simplified to a first or second order block, but what is more useful for hydraulic designers is to leave the details of the components in. The power of the Automation Studio or BathFP or tools like it is that it allows the designer to see the effect of swapping in new parts - not a 4-digit accuracy prediction of what happens, just enough to know if you're on the right track.

I teach at a technical college in the Toronto area, we use Parker stations to run experiments on - the biggest limitation I find is not being able to load the circuit...
PNachtwey (Electrical)
12 Jul 05 22:35
I know what hydraulic capacitance is.  I just don't have values for pipes, hoses, and cylinders.   Hydraulic capacitance is defined by

volume
-------
bulk modulus of oil

This is for the fluid itself in a vessel that doesn't expand.  A cylinder, pipe or hose should have a multiplier like 1.005 for a cylinder which wouldn't expand much or 1.4 for a hose that does.  It is this multiplier that the manufacturers don't provide.  The capacitance value would allow one to easily combine capacitances in parallel or in series by using the same rules as for electrical capacitors.

BTW, the units or dimensions for capacitance is length^5/force or m^5/N in SI units.
The change in pressure is equal to the change in volume / capacitance.
The rate of change in pressure is equal to the flow / capacitance.  Try it! You will see the units work out.

Simulating a simple second order transfer functions is not enough.  It is important to do the hydraulic modeling because of the non-linearitiess.  I use the model to tell me if the system will not work.   If the model works that does not mean the real system will work because there are things like hose that aren't taken into account.   However, if the model doesn't work, the real system will not work.   If the simulator indicates the system just marginally works, the model will give a pretty good idea of what needs to be improved.

Not being able to load the system is a problem.  My problem is that I have only one hydraulic system.   I need to use modeling to test on different systems.

We will look at the BathFP software.   It looks good enough to keep people out of trouble.
EdDanzer (Mechanical)
13 Jul 05 12:28
Sorry to take so long to respond, and I have to make this short, but will try to provide more information over the weekend.
PNachtwey,
I was not trying to say the system didn’t work, or was poorly designed. These were just observation of possible areas of concern when tuning, and over all system stiffness.
Some of the capacitance of a hydraulic system comes from size change due to pressure, and flow restriction through plumbing, fittings and hose ends. Size change from pressure is mostly diameter increase. This link will show diameter change in a barrel for a seal application: http://www.danzcoinc.com/html/step_lock_piston_seal.html
PNachtwey (Electrical)
13 Jul 05 14:05
Oooh.  Good info.  Now I will must figure out how to use it.  I will report back if it makes a signficant difference or not.  At least I will know and can put this nagging question in the proper perspective relative to pipe and hose.  I still think the affects of cylinder swell are small.

BTW, do you have the same kind of data for hose and pipes?  I can just use these values as typical/default values.

I figure you must sell the seals?   If so you must be on top of the subject of cylinder expansion.  I may be back with questions.  What do you know about pipes and hose swell?  Thanks, another star for you.  Maybe, I am giving them out too easily both both cylinder epansion and BathFP links are gold.  Now I just have to fiquire out what to do with them.

All works stops, I figure this out now.

PNachtwey (Electrical)
13 Jul 05 17:50
My conclusion is that cylinder capacitance is too big to be ignored but it can be taken into acount by fudging the bulk modulus of oil and making it a little smaller.  This is normally done anyway to account for air in the oil.

Although the cylinder capacitance changes with pressure, the change is not enough to make a difference and it can be ignored.

ftp://ftp.deltacompsys.com/public/PDF/Mathcad%20-%20cylinder%20capacitance.pdf

Ed, I noticed that you must use Mathcad too.
Back to work.
kcj (Mechanical)
14 Jul 05 10:47
I can open page 2, but barely read it. Should I download to anothe rapplication somehow?
k
PNachtwey (Electrical)
15 Jul 05 1:32
Page 2 of what?   My files are .pdf files.  You can expand them using the Acrobat reader.
HCMechSys (Mechanical)
15 Jul 05 9:10
For tube capacity, the correction for bulk modulus is the same as for the cylinder. I found the correction formula in the Keller reference on pg. 63. As PNachtwey points out the hydraulic capcitance is volume/(effective bulk modulus), with the effective modulus corrected to account for tubing and I guess the cylinder as well. The correction is based on radial strain of a cylindrical pressure vessel.

For line models, BathFP uses a similar bulk modulus correction formula given in Keller. The BathFP formula doesn't involve Possoin's ratio, so all you need for the tube material in question is the Young's modulus. BathFP comes with 3 predefined materials - steel (E=207 GPa), a Aluminum/Nickel/Brass alloy called Tungum (E=117 GPa)- used in marine systems, or "flex hose" (E=4.3 GPa).

I was going to try these different values in the BathFP model I did of PNachtwey's system. But the performance is already not that great and it sounds like he doesn't have measured performance of it anyway. Can you supply more appropriate values (maybe for the system you've got at your office), PNachtwey? I'm going to change the line diameter to 3/8" anyway since this is a more typical value than the 1" I have now. Perhaps I should change the cylinder diameter to 3.25" instead of 2"?

One other thing I spotted in your Mathcad simulation, the formula:
MinRodVol=MinCapVol+0.5*CylLen - not sure the second term is dimensionally correct...both of volumes - Cap and Rod - refer to line volume, correct?
kcj (Mechanical)
18 Jul 05 10:24


pg 2 I was referring to EdDanzer's link

k
PNachtwey (Electrical)
18 Jul 05 13:15
"But the performance is already not that great and it sounds like he doesn't have measured performance of it anyway."

Actually, I do.  I am trying to resolve some differences.   It seems my perfect system works OK for motion control but as a research systems it is lacking.   Ed was right.  The pipe to the rod end is too small.  The outside diamter is .75 inches.
There is also too much hose between the accumulator and the system.   All this hose is 3/4inch inside diameter hose.  One other problem is that the system is on a stand and the stand vibrates.  This vibration adds another frequency to the pressures or net force.

My model and the VCCM formula predict my system should travel at 52 inches per second while extending.  The maximum that it can really do is only 47 inches per second.   My model does not include loss for hose and piping.  I need to get my stuff together before continuing.

"
 Can you supply more appropriate values (maybe for the system you've got at your office), PNachtwey? I'm going to change the line diameter to 3/8" anyway since this is a more typical value than the 1" I have now. Perhaps I should change the cylinder diameter to 3.25" instead of 2"?
"

My system has a bosch NG10 -803 spool 27 GPM valve.  The cylinder is a Purakal 2 x 24" with a 1.375 in rod.  The load is 600 lbs that rolls on wheels.

The reason why I like the idea of capacitance is that is takes into acount the volume.  If the bulk modulus of pipe is used, it still needs to be scaled by the length of pipe used.

Here is a link to a simulation of my system
ftp://ftp.deltacompsys.com/public/PDF/Mathcad%20-%20hydsim-delta.pdf

Reality differs from my simulation in two ways.  The simulation goes faster.  There is nothing wrong with my calculations.  The VCCM formula predicts the same speed.  I just don't my calculations are complete because it doesn't take into acount the hose ( too small and too long ) between the accumulator and the valve and the pipe between the valve and the cylinder's rod end.  If I lower my models system pressure I can get the same results.   Another difference is that the simulation doesn't show the effect of the stand vibrating.   At least I think it is the stand.   Finally,  the graphs of the data is much different extending and retracting.   The extending looks similar to the simulation.   Notice there is no overshoot in the simulation and there isn'[t in the actual system.   However, there is ringing when the system is stopped.  Why.  Does the system go from being underdamped while stopped to overdamped while moving?   In the retract direction the actual system overshoots and looks quite different.  Why?   I think it is the stand and how it is braced.

I can post lots of .jpgs of my physical system.  It would be easier for me just to post the raw data.  This way you can import it into Mathcad,  Excel or our own software that is free on the web and analyze it instead of just look at it.  I need to fix some things before I continue.

   
EdDanzer (Mechanical)
18 Jul 05 14:02
Guy’s,
I was not able to put together the information over the weekend, to many other unfinished projects so this will be short also.
Kcj,
Try blowing up the page by hovering over it and using the expand button or print it.
PNachtwey,
The expansion for the port tube, is done the same as the barrel. Be sure to multiply the diameter expansion by the length to obtain the volume change created by pressure change. What is the wall thickness of the ¾” tube?
When the cylinder is retracting the pressure in the rod side will be higher than then when extending, yet the flow is less. Depending on the direction of movement the back pressure of the oil exiting the cylinder, on each end of the cylinder will be different through the valve because of area differences and plumbing differences.
The vibration could be coming from the valve modulating to maintain the speed demand.
A 27 gpm valve seems large for a 2” bore cylinder, if the valve has to do a lot of metering at full speed the bore to rod flow differences could cause some problems.
It is best to hard plumb the accumulator with large passages as close to the valve as possible for the best performance.
PNachtwey (Electrical)
18 Jul 05 22:53
I think the wall thickness or the pipe to the rod end is .035 but can't say for sure.
 You can see ( look at my .pdf above ) the capacitance change due to pressure expanding the cylinder wall very small.  It can be ignored.
 The pressures in my system are relatively low.  My system pressure is 1500 PSI.  I will do the calculations on the rod end pipe though.
 I admit the rod end pipe is too small because the oil must travel too fast.
Roger the accumulator location and piping.  There is a consensus on that.

At this time I am trying to figure out why the damping factor on my system is so much higher than what most text books say the damping factor should be.   Most books say the damping factor should be about .05 to .1.  My system has a damping factor close to 1 while extending and about .6 while retracting.  


jonnycowboy (Mechanical)
27 Sep 05 11:13
Does anybody have a copy of pc_bathfp that they could send me?  the website dosen't work anymore.
thanks
HCMechSys (Mechanical)
27 Sep 05 20:14
You can get it from:

http://ca.geocities.com/hchesser@rogers.com/pc_bathfp.zip

its the previous (alpha) version, not the version that everyone is waiting for...
jonnycowboy (Mechanical)
28 Sep 05 0:18
thanks incredibly!
95yukon (Mechanical)
10 Dec 05 17:23
Try this - you can do just about anything but drive the vehicle right out of the screen.  

http://www.cat.com/cda/components/securedFile/displaySecuredFileServletJSP?fileId=96607&languageId=7

If this is too much, Hysan from Hydrasoft is something I've used in the past that allows you to model components / systems.

I'm not aware of hydraulics simulation software that individuals can afford - they are very costly to develop.
PNachtwey (Electrical)
17 Mar 06 18:56
We just bought a copy of 20sim.  It has saved us a lot of time because we can simulate so many different sizes of hydraulic servo systems.   We can even simulate the whole machine shaking as it moves because the machine is not bolted to the earth.   It would have cost me much more to write anything approaching 20sim so I think it is a bargin.

http://www.20sim.com/
EdDanzer (Mechanical)
17 Mar 06 23:35
Did you get Standard or Professional?
How easy is it to learn?
Gkranz (Mechanical)
31 Mar 06 11:18
Quote: "Actually I do not think there are too many people who can design a proper hydraulic circuit at all."

Another quote: "I have up to now used so called hydraulic specialists working for the big hydraulics suppliers to do the hydraulics for my designs and boy more often tham not I have problems, ranging from overheating to functionality issues."

This subject comes up every so often and we get the same answers in the posts. Correct answers;

Stop trying to get FREE designs by purchasing components, and then complaining about poor designs. Second, there are very good hydraulic designers out there working, but you know what, they do not charge for the design, then give you free parts?

Hydraulic simulation software - I have used most including Easy5, and again without expernice and knowledge, correct inputs of data and knowing how to interpet the results. These packages simply get you to the wrong answer faster than without them.

Software for dummys is what most people are looking for, and we are not there yet.  "We can even simulate the whole machine shaking as it moves because the machine is not bolted to the earth."  I really like this one, only Peter could come up with a statement like this, gotta love this guy?

Westerndynamics.com

frans (Mechanical) (OP)
31 Mar 06 16:54
Obviously it touched a nerve with you Gkranz. Fact is, component suppliers offer to do the design - it is part and parcel of their offer: They claim to employ design engineers, they offer to quote on what you need, they provide you with a hydraulic circuit schematic listing the required components - they are doing the design. It is not about free or not free - you pay for it in the price of the components for sure.

Rest assured, I do not mind paying and in fact I have now found an independent that I use (and pay).

I agree with your notion about garbage in and garbage out in relation to software for dummies. I am irritated with the hydraulics component suppliers because they do not deliver to me what they promised. By own admittance I am not an expert, I do not have the time or potential immersion to become one either. I am not talking about reading a circuit - I can do that too - I am talking about the type of experience only a professional in an industry can have. I have an obligation to my customers to make sure what I build works and continues to do so.
Gkranz (Mechanical)
31 Mar 06 18:56
Dear frans,
Didn't bother my nerves at all. I think your kidding yourself about suppliers offering to do design.

First you never see a seperate line item charge for design?

Second, if you take the time to check component pricing, it is the same with or without their help.

Component suppliers are like Wal-Marts, one on every corner and the hook they use is "we can design circuits for you if you buy the parts from us, we are designers?

When something does not work, the warranty is limited to component replacement or repair, never design. Generally it is the way you used or put "their" design together that comes out of their mouth when circuits do not work.

Do you have any performance contract, who owns the design when it is given to you, are we free to pass it around to your customers, who pays when the circuit does not work, and have you provided an out line of what and how the circuit should work.

"I am irritated with the hydraulics component suppliers because they do not deliver to me what they promised." With all due respect, it was your nerve that is hurting not mine.

I do not know your location, but out West (Oregon, Washington) suppliers do manifold designs for customers, only one small problem though. None of them will give the customer a copy of the manifold drawing, just a circuit drawing, that way no one can shop the price around and you are locked into them for more manifolds.

Nothing wrong with component suppliers, if you use them for their intended purpose, selling parts.  Well anyway, hope things work out better for you and your customers.
Best Regards,
Gkranz


Westerndynamics.com

PNachtwey (Electrical)
1 Apr 06 10:02
"Did you get Standard or Professional?"
We got the standard.  1 seat.

"How easy is it to learn?"
It didn't take too long to get the basics.  It has its own programming language.  You should know how to program if you want to create your own projects.

There are demo versions at 20sim.  Try it.  We are going to make an example hydraulic servo actuator project that those with the demo version of 20sim can load.  Unfortunately there will be a lot of parameters to modify.  I will post it on our FTP site when we are done.  That way those with BathFP can compare.

"These packages simply get you to the wrong answer faster than without them."

Yes, and you must know enough to sanity check the results.
Simulators will not think for you.  You must still understand the physics of hydraulics to design a good system.  However, the simulator will show flaws is designs faster if you can interpret what you see correctly.

"Software for dummys is what most people are looking for, and we are not there yet."
We never will be.  The dummys must get smarter.

""We can even simulate the whole machine shaking as it moves because the machine is not bolted to the earth."  I really like this one, only Peter could come up with a statement like this, gotta love this guy?"

Have you ever been in a saw mill where the machine are mounted on steel frames in the air instead of bolted to the concrete below?  The whole frame shakes when the actuators move heavy loads like logs and saws quickly.  When the whole frame shakes it is absorbing energy that should have gone to moving the actuator and load.  This is a problem since we are trying to move actuators accurately and not the mill.  The more compliant the foundation is the more energy it will absorb.

A lot of what I do deals with how energy is moved from one point to another and how quickly it can be moved or removed.
If takes a LOT of power over short periods of time, to compress oil rapidly.
HCMechSys (Mechanical)
1 Apr 06 22:30
"We are going to make an example hydraulic servo actuator project that those with the demo version of 20sim can load.  Unfortunately there will be a lot of parameters to modify.  I will post it on our FTP site when we are done.  That way those with BathFP can compare."

Sounds good, I'd like to give it a try with BathFP...
Gkranz (Mechanical)
3 Apr 06 0:01
Quote - "Have you ever been in a saw mill where the machine are mounted on steel frames in the air instead of bolted to the concrete below?"

And Peter, these steel frames just float in mid air not conected to earth?  I always get a kick out of cutting logs down to 0.0005, when I go to buy 2x4, cannot find any two the same size.  And the saw filer sharpens the saws +/- 1/8 of an inch.

Quote - "A lot of what I do deals with how energy is moved from one point to another and how quickly it can be moved or removed."

And we call that hydraulics Peter?
As always Peter, take care old buddy.
Best Regards,
Gkranz




Westerndynamics.com

PNachtwey (Electrical)
3 Apr 06 10:58
"And Peter, these steel frames just float in mid air not conected to earth?"
Sometime not well enough.

"  I always get a kick out of cutting logs down to 0.0005, when I go to buy 2x4, cannot find any two the same size.  And the saw filer sharpens the saws +/- 1/8 of an inch."

At least the hydraulics controlled by our controllers aren't responsible for that.

"And we call that hydraulics Peter?"
I wish more hydraulic designers did.  You know as well as I do that the text books you and I have deal with constant or steady state velocity calculations, not acceleration or jerk which involve moving energy in and out of the system.  The best most can do is calculate F=m*a with the assumption force and acceleration don't change.  Required power is just Force*velocity.  Never have I seen Pcap(t)*Acap-Prod(t)*Arod - friction(v) = m*a(t) except in hydraulic modeling software.



Gkranz (Mechanical)
3 Apr 06 11:10
Ha, Ha.  I agree with you, I just like giving you a hard time.
Best,
Gkranz

Westerndynamics.com

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