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Author Topic: How to? Long accel/decel profile  (Read 6312 times)

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How to? Long accel/decel profile
« on: November 29, 2012, 01:38:14 AM »
I will be moving a small object fast back and forth on an 80 ft. rail using one large stepper motor/driver and cable.  I need to program a smooth acceleration / deceleration profile evenly over the whole length.
Can Mach3 run this? 
TIA !

Offline BR549

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Re: How to? Long accel/decel profile
« Reply #1 on: November 29, 2012, 01:43:56 AM »
It depends on about 100 different things.

(;-) TP
Re: How to? Long accel/decel profile
« Reply #2 on: November 29, 2012, 01:58:33 AM »
OK BR549, let's narrow it down.  Step resolution is not too important, high speed is.  If the motor has about 1200 oz in. torque maybe I can drive an 8 dia drive wheel and idler wheel to move the cable at a high linear speed.
Can I program exact number of steps for the whole length and plot them along their curves?  Can Mach3 or another program compute the curve?

Offline BR549

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Re: How to? Long accel/decel profile
« Reply #3 on: November 29, 2012, 03:01:46 AM »
You have the Motion planner and the accelleration and velocity settings that are a trap curve and that is it.  IF you plan to wind it up on a drum then you also have variable diameter as the cable winds onto the drum.  Without positive engagement you can have cable slippage on the sheave.

Steppers are NOT known for their high speed. They are low speed motors. Low resolution to gain speed can drive you into the cogging problem and step loss when driving them beyond their torque curve.

Servos have a much wider operational rpm band.

I think you may want to take a look at a good VFD and motor drive setup.

How fast and what accelleration rates are you talking about ?

What is the accuracy needed for the stop points ?

(;-) TP



Re: How to? Long accel/decel profile
« Reply #4 on: November 29, 2012, 09:12:46 AM »
I'd use one of these to do what you want.

http://motion.schneider-electric.com/products/mdriveplus_overview.html?gclid=CL2Q7aCr9LMCFSemPAodJE8AlA

You can write a program and download it to the unit.

Self contained just need a Power Supply and a means to trigger input the program to start and stop. One trigger to send it home, trigger to start, trigger to stop and what ever you can think of. You can change/set the accel/decel and speed during the program run. You just write a text program and then send it to the processor. Different programs can be run depending on the trigger that is sensed. Great for repeated routines. Fun units to work with too. But Servos are so much faster and more powerful, Parker makes a GV Drive that does this also to control Servos that I have used.

Offline ger21

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Re: How to? Long accel/decel profile
« Reply #5 on: November 29, 2012, 11:47:28 AM »
The new Gecko G215 can do this on it's own, but it hasn't been released yet.
Gerry

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Re: How to? Long accel/decel profile
« Reply #6 on: November 29, 2012, 12:14:13 PM »
Thanks Gerry for the heads up
« Last Edit: November 29, 2012, 12:16:13 PM by Ya-Nvr-No »
Re: How to? Long accel/decel profile
« Reply #7 on: November 29, 2012, 04:38:19 PM »
I think you are right about servos vs. steppers.  I will plan for that.
0 to 80ft. in .5 to1 sec. moving object about 4oz. mass.  Acceleration gentle and decel the same.  But the veloc. profile needs to be sinusoidal so at midpoint (40ft) accel ceases and decel starts.  Decel could be triggered by a switch at midpoint. 
The minor amount of slip can be corrected for and zeroed each cycle by switches along the slide and a home switch.
You mentioned the Gecko G215 as a possible dedicated controller without need for a PC.  Any other options off the shelf?
The big unknown for me is how to program the specific velocity profile.
Thanks all.

Offline BR549

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Re: How to? Long accel/decel profile
« Reply #8 on: November 29, 2012, 05:11:59 PM »
80 foot in less than a sec ? That is not going to happen with Mach3.


There is NOTHING gentle about that motion curve (;-)

(;-) TP
Re: How to? Long accel/decel profile
« Reply #9 on: November 29, 2012, 05:26:21 PM »
"gentle" meaning zero velocity at each end during reversal. 

"...That is not going to happen with Mach3..."
Can Mach3 be tricked into thinking the move's more conventional by using normal speed in the instructions but multiplying the motor steps in the driver settings to increase actual distance traveled?