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?
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?
RE: Choosing kinematics software?
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?
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?
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?
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?
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?
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?
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?
RE: Choosing kinematics software?
RE: Choosing kinematics software?
RE: Choosing kinematics software?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Choosing kinematics software?
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?
RE: Choosing kinematics software?
Who did you contact at Algor?
Garland
Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
RE: Choosing kinematics software?
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?
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?
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?
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?
I guess specifying a friction FORCE (rotating with body = ON) will give the same problem you desribed above.
RE: Choosing kinematics software?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Choosing kinematics software?
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?
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?
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?
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?
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?
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?
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?
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?
I will try posting pictures later today.
RE: Choosing kinematics software?
http://picasaweb.google.com/EdDanzer/EngTip/
RE: Choosing kinematics software?
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?