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Topic: Position control (Read 2548 times) previous topic - next topic

Hey guys....I need your advice on making a decision.

I am trying to make an actuator to push a hydraulic clutch master cylinder and I don't want to sped over $1000 on it. I am curious if I can get accurate position control probably within the .0325" range if I use this magnetic encoder http://store.makerbot.com/magnetic-linear-encoder-v1-2-kit.html

And I want to control the position of this actuator http://www.parker.com/portal/site/PARKER/menuitem.de7b26ee6a659c147cf26710237ad1ca/?vgnextoid=fcc9b5bbec622110VgnVCM10000032a71dacRCRD&vgnextfmt=EN&vgnextdiv=&vgnextcatid=6147618&vgnextcat=COMPACT+EHA+ELECTRO-HYDRAULIC+ACTUATOR&Wtky=ACTUATORS

I am also curious if I should use a rotary encoder to send a signal for the position or should I use a potentiometer?

I want to hook it all up to the arduino so that when I pull a lever the rod moves in conjunction with how much I pull the lever, if the lever is half pulled then the rod is half extended. I want full range control of the rods position via the lever.

I am super new to the arduino stuff but I do have a basic understanding of how things work, I need your opinions before I spend $500 on the actuator.

Let me know if this will work.

Thanks,

zoomkat

Quote
I am trying to make an actuator to push a hydraulic clutch master cylinder and I don't want to sped over $1000 on it.


Perhaps you should consider getting an electric linear actuator that has an internal pot (probably less than $150).
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Quote
I am trying to make an actuator to push a hydraulic clutch master cylinder and I don't want to sped over $1000 on it.


Perhaps you should consider getting an electric linear actuator that has an internal pot (probably less than $150).


Can't....not enough force vs speed I can get high force but low speed and vice versa!

Need to move a clutch master cyl 1.2" as fast as possible!

zoomkat

Quote
Need to move a clutch master cyl 1.2" as fast as possible!


How fast? How much force required? In automotive clutch applications the speed of a master/slave hydraulic system may be limited by the size of the tubing connecting the two cylinders. Are you sure the electrohydraulic actuator you have chosen will meet your specifications? In hydraulic systems that require quick response, pressurized accumulators are usually used as the hydraulic pumps themselves may not move the fluid very fast.
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Quote
Need to move a clutch master cyl 1.2" as fast as possible!


How fast? How much force required? In automotive clutch applications the speed of a master/slave hydraulic system may be limited by the size of the tubing connecting the two cylinders. Are you sure the electrohydraulic actuator you have chosen will meet your specifications? In hydraulic systems that require quick response, pressurized accumulators are usually used as the hydraulic pumps themselves may not move the fluid very fast.


This is a stand alone hydraulic unit with built in resivoir and pump.....max speed of unit is 3.1" a second and it has a hiqh force that will be adequate for what I am doing. This actuator will work but it is just a dc motor driving it! I need some sort of position control for my application.

Thanks,

zoomkat

Quote
This is a stand alone hydraulic unit with built in resivoir and pump.....max speed of unit is 3.1" a second and it has a hiqh force that will be adequate for what I am doing. This actuator will work but it is just a dc motor driving it! I need some sort of position control for my application.


You could attach a linear pot to the moving shaft, or simply use foward and reverse travel limit switches.
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John_S

Quote
I am curious if I can get accurate position control probably within the .0325"
I doubt you could get that sort of positional accuracy. Hydraulics tend to be for brute force rather than pinpoint precision. having a system that's capable of such precision would require the right pump and valves rather than any electronic position sensor.
http://jsrintervalometers.blogspot.ca

retrolefty


Quote
I am curious if I can get accurate position control probably within the .0325"
I doubt you could get that sort of positional accuracy. Hydraulics tend to be for brute force rather than pinpoint precision. having a system that's capable of such precision would require the right pump and valves rather than any electronic position sensor.


I strongly disagree. I worked at a oil refinery and we used many different forms of hydraulic actuators for things like throttle control on large steam driven turbines and other large mechanical equipment. Such control required very high precision positioning and a well designed system could have both large brute force strength combined with pinpoint precision. Typical position feedback sensors used were LVDT sensors ( http://www.ni.com/cms/images/devzone/tut/a/f841fe69729.gif ) mechanically coupled to the moving actuator arm or shaft. Electronic P&ID controllers were used to sense the actual position Vs desired position (setpoint) and drive the electro-hydraulic control in a classic feedback loop. The various electro-hydraulic components were very expensive made to very tight tolerances, there was no slop and minuet movements as well as fast movements could easily be made.

Lefty


Quote
This is a stand alone hydraulic unit with built in resivoir and pump.....max speed of unit is 3.1" a second and it has a hiqh force that will be adequate for what I am doing. This actuator will work but it is just a dc motor driving it! I need some sort of position control for my application.


You could attach a linear pot to the moving shaft, or simply use foward and reverse travel limit switches.


If I use a pot as a feedback device then use another pot as an input device to change the position? For every change of voltage the shaft will move a certain distance? Would that work?

retrolefty



Quote
This is a stand alone hydraulic unit with built in resivoir and pump.....max speed of unit is 3.1" a second and it has a hiqh force that will be adequate for what I am doing. This actuator will work but it is just a dc motor driving it! I need some sort of position control for my application.


You could attach a linear pot to the moving shaft, or simply use foward and reverse travel limit switches.


If I use a pot as a feedback device then use another pot as an input device to change the position? For every change of voltage the shaft will move a certain distance? Would that work?


In theory, yes. I reality it depends on the quality, resolution, environmental ruggedness of the pot as well as how well and backlash free your mechanical connection to the pot is. The only time I saw pots used in commercial actuator applications is where it was built inside the actuator body itself.

Lefty

John_S

Lefty, I didn't know about hydraulics as you described. I've only used typical farm implements (front end loader, dump wagon, ect).

I think we are both correct though. Hobbyist-budget hydraulics are not meant for pin-point precision, although with the right equipment (and money) it could be done.
http://jsrintervalometers.blogspot.ca

retrolefty


Lefty, I didn't know about hydraulics as you described. I've only used typical farm implements (front end loader, dump wagon, ect).

I think we are both correct though. Hobbyist-budget hydraulics are not meant for pin-point precision, although with the right equipment (and money) it could be done.


Actually I didn't know there were any hobbyist-budget priced hydraulic components available. Perhaps if purchased surplus or second hand?

Lefty

The actuator I listed is high speed and good precision, it's priced at roughly $6-700 bucks. Is anyone able to point me in the right direction of creating the position control for this?

Thanks,

zoomkat


The actuator I listed is high speed and good precision, it's priced at roughly $6-700 bucks. Is anyone able to point me in the right direction of creating the position control for this?


What in the specs you provided for your actuator implys it has "good presision"? it appears that this is the product of "wishful thinking" to make the actuator work for your project.
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