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Choosing kinematics software?

Choosing kinematics software?

Choosing kinematics software?

(OP)
We are doing more product design utilizing hydraulic cylinders to drive structures that must be light weight and robust. I have used Working Model and COSMOSMotion both, neither have a way to input acceleration rate, deceleration rate, maximum velocity and force into one element to simulate a simple linear actuator.
What is the best software to do this type of kinematics with so the pin forces and direction can be accurately be input in to the FEA model?

RE: Choosing kinematics software?

I don't use it myself, but I've heard good things about ADAMS (an MSC product, I think)

RE: Choosing kinematics software?

I think you may be expecting too much. I could do what you describe in ADAMS, but would use more than one component, by choice. Similarly, I could do it in in WM3D, and again, I'd use more than one element.

It might be possible to abstract the performance of the actuator down to one equation, but I'd rather try and model the processes that cause the non linearities.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

EdDanzer,

Are you saying that within your complex model of multiple lines, plates etc, that you are trying to apply the accelerations/decelerations, velocities, etc. to a single element?  If so, although I don't use the programs you mentioned, I would think they would still be able to do it...you may just have to be a little creative.  It wouldn't be a purely kinematic analysis...more like an event simulation, but I'm not sure I understand your real question.  

The accelerations, decelerations, and velocities would be determined by a single input curve as either a displacement vs. time curve using prescribed displacements or some derivation of this curve using other input types.  

I'm not sure what you are doing with the "Force"...are you trying to drive the cylinder using the forces but still apply the velocities and accelerations?

Sounds like an interesting problem...at least what I understand of it.

RE: Choosing kinematics software?

Just tinking about it you can do it in working model, but it is a bit ugly.

I can't remember the syntax for the arguments, but basically if you want to do it in a single component you need to build a single line expression for the force output of the actuator.

Here's what I would do in Working Model: simple force actuator, in parallel with a damper, to give your friction and speed limits, all in series with a mass, to govern your acceleration. If deceleration is via a different mechanism then just put in a whole second block similar to the above, in parallel.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

(OP)
Greg,
I have not looked at Working Model since 2002. At that time the acceleration rate was relative to the force value of the actuator. A low input force gave a low acceleration rate and a large force gave a high acceleration rate.
I used a 4” bore cylinder at 1000 psi, and at 15,000 psi in one example. At 15,000 psi the acceleration rate used required over 1000 hp. This gave bogus pin and contact forces so it took many steps and some hand calculations to have meaningful data.

GBor,
I’m not trying to do complex simulations. Any simulation should represent real world features. To simulate movement of a linear or rotary actuator and see the results of its interaction with the components it interacts with it is mandatory to provide a maximum acceleration rate, acceleration force, maximum velocity, maximum force available, deceleration rate and deceleration force. Many times these values are relative to the power available to drive the system and simple to define.
Hydraulic cylinders driving arms on an excavator are one example. The lift or dig force is relative to boom position and working pressure. The speed is flow driven, and the acceleration is engine power driven.

Has anyone used SimHydraulics™?

RE: Choosing kinematics software?

Hi,
I seem to remember that you can do that with CosmosMotion by using ADAMS' arguments & functions in the "motion generator" (CM's kernel is the simplification of ADAMS', but it accepts the same "language"). Btw, the latest versions of CM have probably improved a lot under this point of view. I can't be more specific because the last version of CW I saw was 2004...

Regards

RE: Choosing kinematics software?

My vote goes for Working Model.  But, it is not going to be a straight forward task, as Greg pointed out.  (Most of my experience lies in WM2D - quick and it allows me to evaluate conceptual layouts even before 3D CAD details exist - granted that 3D effects are not important).    

It is likely that you will have to scratch your head and enter formulas/expressions and not simply values when defining your actuators.  To handle limits you could make use of conditional formulas or make use of the "if" statement.  There is also an "Active when..." option when specifying actuators.  

But, of course, having sorted this out once, it will be easier for subsequent simulations.

Regards

RE: Choosing kinematics software?

I haven't used ADAMS/Hydraulics, but I really find it hard to believe it does not cover this in exhaustive detail. A quick look at the Help file reveals the following topics

    Connecting Hydraulic Ports  
    Creating Components  
     Accumulator  
     Cartridge Valve3p  
     Valve2  
     Check Valve3p  
     Check Valve4p  
     Counter Balance Valve4p  
     Cylinder1  
     Cylinder1f  
     Cylinder2  
     Cylinder2ff  
     Directional Control Valve2w2  
     Directional Control Valve3w2  
     Directional Control Valve4w3  
     Flow Control Valve2  
     Flow Source  
     Fluid  
     Force Source  
     Generic Pump/Motor2  
     Generic Junction2  
     Generic Junction3  
     Generic Junction4  
     Laminar Orifice  
     Mass1  
     Orifice  
     Pipe 1  
     Pipe 2ff  
     Pipe 2pf  
     Pipe 2pp  
     Pressure-Reducing Valve3  
     Pressure Relief Valve2  
     Pressure Source  
     Pump/Motor3  
     Reservoir2  
     Restrictor Valve2  
     Servovalve4w3  
     Shuttlevalve3  
     Spline Orifice  
     Sum of Flows  
     Sum of Flows2  
     Sum of Flows3  
     Sum of Flows4  
     Tank  
    Disconnecting all Hydraulic Ports  
    Disconnecting a Single Port  
    Hydraulics Copy  
    Hydraulics Default Set  
    Hydraulics Delete  
    Hydraulics Rename  
    Hydraulics Reorient  
    Modifying Components  
     Accumulator  
     Cartridge Valve3p  
     Check Valve2  
     Check Valve3p  
     Check Valve4p  
     Counter Balance Valve4p  
     Cylinder1  
     Cylinder1f  
     Cylinder2  
     Cylinder2ff  
     Directional Control Valve2w2  
     Directional Control Valve3w2  
     Directional Control Valve4w3  
     Flow Control Valve2  
     Flow Source  
     Fluid  
     Force Source  
     Generic Pump/Motor2  
     Generic Junction2  
     Generic Junction3  
     Generic Junction4  
     Laminar Orifice  
     Mass1  
     Orifice  
     Pipe 1  
     Pipe 2ff  
     Pipe 2pf  
     Pipe 2pp  
     Pressure-Reducing Valve3  
     Pressure Relief Valve2  
     Pressure Source  
     Pump/Motor3  
     Reservoir2  
     Restrictor Valve2  
     Servovalve4w3  
     Shuttlevalve3  
     Spline Orifice  
     Sum of Flows  
     Sum of Flows2  
     Sum of Flows3  
     Sum of Flows4  
     Tank  
 
 

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

(OP)
Adams/Hydraulics is not in COSMOSMotion. They do not have any accurate way to define a linear actuator. The only force options are a Springs, Dampers, Bushings, Action Only and Action/Reaction.

RE: Choosing kinematics software?

Can you use a thermal expansion to cause the force?

RE: Choosing kinematics software?

(OP)
The concern with thermal expansion would be rate and distance. Some cylinders move at 3ft/1m per second but most move less than 60ft/18.3m per minute. Strokes go up to 40ft/12m or more.

RE: Choosing kinematics software?

OK, so what are you going to do? It sounds like the problem is solvable in the right software, but not necessarily in COSMOSMotion.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

(OP)
I have sent some information to Algor and am waiting for a response. I’m waiting for a call from Mathworks about a demo. Mathworks stuff is less money than Algor but can do other things. Mathworks does not tie into CosmosWorks so data will have to be manually input so the results won’t be as good as Algor.
I have contacted CosmosWorks again about a time line commitment for a simple solution but no answer.

Today it Sucks to be me!

RE: Choosing kinematics software?

Have you looked at FEDEM?

RE: Choosing kinematics software?

(OP)
Fkmeyers,
I will look at FEDEM since I’m not familiar with it.

GBor,
The sales guy is Ed Simmons, and I can’t remember the technical guys name.

RE: Choosing kinematics software?

Had a play in WM. I built a system that would do what you asked, more or less.

Link a pair of coords by a rigid joint on a slot. join them with a linear actuator. Change it to a force type. Enter your raw force expression. Add a mass to the moving end, to limit the max accel. Add a spring between the same two coords. 0 the k part, change the damping element to limit the max speed.

It would be easy to build a pump block to create a pressure vs flow rate source, and use that pressure to drive the force actuator.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

Hi,
it seems like a great solution, GregLocock.
I don't have understood very well if the O.P. is already using something of the CosmosWorks family, since the very same solution you describe can be very easily done in CosmosMotion, if he needs.

Regards

RE: Choosing kinematics software?

I also added a pure friction term... and discovered why you never do that.

The seal/ring friction in a shock absorber is of the order of 300N, so I added a force actuator which supplied a force of

300*(1-2*(shock.v.x<0))

As you can imagine it never stops moving, it just jitters around the equilibrium position. Real systems don't do that, I need to think of a better way of modeling friction. Funny though.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

Greg, I did not look into this but if you could align a slot with the prime actuator, WM2D allows you to model friction via the script menu (by simply specifying the coefficient).

I guess specifying a friction FORCE (rotating with body = ON) will give the same problem you desribed above.

RE: Choosing kinematics software?

A damping element of type -c (as opposed to -c.v) looks like friction, but seems to apply just a constant force, it doesn't oppose the direction of motion. I'll have a dig around for a better friction model, it is a bit interesting to me.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

(OP)
GregLocock,
The problem with adding mass for limiting the max acceleration is you change the acceleration forces, output forces at different positions, and inertia when stopping.

I talked with Hari Padmanabhan with Cosmos today about what I was trying to do and how to implement it. The short answer is I want to see the resultant actions of a solid model driven by an off shelf drive energy source. Examples of an energy source are a servo motor, electric motor, hydraulic motor, air motor, linear electric motor, air cylinder, electric cylinder and hydraulic cylinder. This would be like testing a car with different engine power to now how it would affect the frame or other components.
It appears that current Kinematics software does not model power available. You can assign part of the power components to a model but not all in the same study at the same time.

RE: Choosing kinematics software?

"It appears that current Kinematics software does not model power available."

Well, I don't really agree. For example, in my powertrain model (which plugs into my standard vehicle model) I'd have an engine torque vs rpm curve. Then my driver model applies a certain throttle %age. The solver looks up the current rpm, and delivers that % of that torque to the crankshaft. This then goes through the rest of the driveline model, via inertias, springs, damping, gaps and gears and whatever, to the contact patch.

That's overkill for most vehicle dynamics work, but it is there.

So the problem seems to be that the kinematics software bundled with Cosmos is less powerful than the standalone products. I don't think that is surprising - using ADAMS less than 2 days a week would be frustrating, and I normally edit the code by hand, in parallel with the GUI.

"The problem with adding mass for limiting the max acceleration is you change the acceleration forces, output forces at different positions, and inertia when stopping."

Sure. All of these models work better if you don't trick them, but model the actual process in the mechanism. So if your pump has an inertia, put it in. If the fluid in the lines has an inertia, put it in. If there is a pressure restrictor, or a one way valve, put it in. Replacing a 5 element block, as suggested above, by one transfer function is /possible/ but is hard to debug.

As another example my power steering model has a simple pressure vs engine rpm vs flowrate delivery map to represent the hydraulic pump side. That's not really good enough for what I want, so the next step is to put the hoses and so on into the model, as I am interested in elasticity and resonant effects. I could cheat and add some arbitrary first order systems in there to represent those resonances, but ultimately it is more robust to model the real system than abstract it down to a very complex equation.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

At the risk of upsetting Garland (Garland, I am apologizing in advance here) I would say just be careful before buying Algor.  I will say no more on the subject.  You have been advised.  

I do not use motion software myself but have found the nonlinear transient analysis capability in Nastran to be adequate for my needs.  I would recommend the below motion package that a colleague is using and swears by...

http://www.fedem.com

Check them out and lets us all know


RE: Choosing kinematics software?

Come on, Frank, surely you don't think I get upset just because you disagree with me?  Actually, I didn't bring Algor up...I hope you noticed that atom

I'm not convinced that I understand the problem and Greg seems to have a working solution.  I do know that Algor has a function coming out that may be appropriate, but this problem seems like it should boil down to a well-planned time-displacement curve to handle the velocities and accelerations.  I apparently don't understand the force issue and really haven't taken the time to try and get it...I called Ed Simmons to make sure he understood.

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group

RE: Choosing kinematics software?

(OP)
Greg,
The problem with tricking the system is sometime you trick yourself into thinking you have done the tricks correctly. That is what I have been doing and probably increases the total design time by a factor of 2.
I need to do 1 or 2 studies per month maximum. If the ability to input values for motors and cylinders are not similar to what you read in the manufactures specifications then you have to translate them. Like translating languages or units of measure, the chance of making a mistake goes up especially if you don’t use those methods regularly.

Fkmeyers,
I sent contact information to Fedem but no response yet.

GBor,
I received a response from Algor late yesterday and I’m not sure they (or maybe it is me) how your input power affects driving a structure.

If you look at setting up a servo drive on a CNC machine control your motor and amplifier limit the acceleration rate and maximum velocity of the motor. The control will work for small machines or big machines depending on how you program the drive parameters. If  we have a CNC machine we need to run a heavier than specified part on if we reduce the acceleration, deceleration and maximum velocities we can run the part without damaging the drive system.

RE: Choosing kinematics software?

Ed,
I am a Fedem Employee, and would like to come with some enlightenment, if possible.

From what I understand of your problem, Fedem is quite capable of doing what you want in some way or another. Fedem has a simple control system module that lets you control most input parameters for the different elements. (Springs, prescribed motions, Forces etc.) A common thing is to actually model the actuators in the model (like electric motors) using the control system, and apply the resulting force to the appropriate part. Often including some speed-measurement etc.
 
In addition Fedem is designed to work directly with FE-parts,
making it possible to get the structural results directly.

But I am not quite sure that I actually understand what you are looking after. When you say "off the shelf energy source" dou you mean you have a fixed set of them, and want to test new designs with all of them ? Or do you think in means of a general parameterized energy source ?

Anyway I am quite sure that you can do it in Fedem, but I do not understand enough to say how easy it will be to build the model.

Jacob Støren
Fedem Technology AS

RE: Choosing kinematics software?

(OP)
Storen,
 We do need to use “off the shelf energy source” item. With hydraulic cylinders we can obtain some bore and rod size combinations at a lower cost so we try to use them first. We start a design by making a basic structure with pin locations to obtain the range of motion the customer requires, then we add the customers load to see if the performance requirements are met. It is best to do 4 to 6 “what if” studies with different geometries and a few different cylinder sizes to be comfortable meeting the customer’s needs, manufacturability and cost of manufacture. The pin load information is used for FEA of the structure.

RE: Choosing kinematics software?

Danzer,

As I understand, your original question had to do with a simple way of modelling hydraulic cylinders/linear actuator based on accelerationrates, max forxe and max velocity.

Fedem has no component that does that out of the box, but it can be built using the control system and some standard elements. Which means that the parametres you want to enter can be entered in the model (and subsequent models) directly.

I would like to check out how to do this in our software if you would help me with the information on how it is supposed to work.

The main thing I am uncertain on is what "driving" input you want on this actuator?

The geomerty/hardpoint positions is very fast and simple to change in Fedem. You do not need any Cad models while experimenting.

The pin loads can be exported to ASCII, DAC and RPC3, but the best thing would be to use your FE models directly in Fedem to skip the export/import loads step, I guess.

Jacob Støren
Fedem Technology AS

RE: Choosing kinematics software?

(OP)
The last project I worked on had to be modeled with 4 different standard hydraulic cylinders. The product is a roll out bucket for a front end loader. The movement is 95° and the bucket with material weighs about 17,000 lbs. The goal was actuation at 2000 psi into the cylinder (14,000-25,000 lbs. force) .5 G max acceleration, and 5 seconds to move the 95°.
I will try posting pictures later today.

RE: Choosing kinematics software?

That mechanism is easy to analyse in WM or ADAMS. The thing that makes it hard is your desire for a simple black box to replace the hydraulic cylinder.


It could certainly be done - by writing a user subroutine in ADAMS. For example, our electronic stability control software is a black box, that gets called by the solver during the run, which just gives it the necessary state variables, and gets the black box output back.

Perhaps it would be easier to write a user subroutine that would generate the appropriate lumped model for you - so when you clicked on the cylinder it would ask you for the five parameters (or however many it is), it would then create the aprropriate geometry connectors and parts, and then you'd run the model in the usual fashion. That's how I build varaible ratio steering racks, the manufacturer has supplied a subroutine that cranks out the model, given a few user specified values.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Choosing kinematics software?

(OP)
Thanks for all the feed back I have contacted all the vendors posted. When I have more information I will let you know.

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