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shantia
science forum beginner
Joined: 07 Apr 2006
Posts: 3
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 Posted: Mon May 22, 2006 11:45 pm Post subject:
non-continuous torque transmission
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hi all
I'm having a problem in a device. its a centrifuge in fact
it has to work in two deferent speeds : 10000 rpm to perform its main
task and a speed of that small that can simply be controlable to locate
the rotor in desired angular locations.
for first speed I am going to use a high speed DC motor but because of
the accuracy of the angular positioning in the second step I have to
use a stepper motor to turn the rotor.
so stepper motor will be connected to the shaft of the rotor by some
kind of for example timming belt.
whenever we need the accuracy we will turn the rotor by stepper and
the main high speed motor will be off but
when we run the high speed motor the stepper has to turn because they
are in fact connected through timming belt . the problem is that the
stepper and timming belt would not tolerate this high speed of about
10000 rpm.
the idea is to cut the torque transmission to the stepper when main
high speed motor is running . but clatch is not acceptable because of
the slipage in clatch that will destroy the accuracy we need.
anybody has any practical Idea or some similar experiences?
thanks in advance
all replays would be appreciated
regards , Shantia |
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Charly Coughran
science forum beginner
Joined: 09 May 2005
Posts: 22
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| Posted: Tue May 23, 2006 3:33 pm Post subject:
Re: non-continuous torque transmission
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"shantia" <amin.zaribaf@gmail.com> wrote in news:1148341542.587579.79500@
38g2000cwa.googlegroups.com:
| Quote: | hi all
I'm having a problem in a device. its a centrifuge in fact
it has to work in two deferent speeds : 10000 rpm to perform its main
task and a speed of that small that can simply be controlable to locate
the rotor in desired angular locations.
for first speed I am going to use a high speed DC motor but because of
the accuracy of the angular positioning in the second step I have to
use a stepper motor to turn the rotor.
so stepper motor will be connected to the shaft of the rotor by some
kind of for example timming belt.
whenever we need the accuracy we will turn the rotor by stepper and
the main high speed motor will be off but
when we run the high speed motor the stepper has to turn because they
are in fact connected through timming belt . the problem is that the
stepper and timming belt would not tolerate this high speed of about
10000 rpm.
the idea is to cut the torque transmission to the stepper when main
high speed motor is running . but clatch is not acceptable because of
the slipage in clatch that will destroy the accuracy we need.
anybody has any practical Idea or some similar experiences?
thanks in advance
all replays would be appreciated
regards , Shantia
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Some additional details (size, hp, positional accuracy needed etc.) would
make it easier to visualize, but here are a couple things you can think
about.
Since you have the DC motor, if you put an angular position feed back
sensor (absolute optical encoder, hall effect sensor, laser reflection
targets) on the centrifuge, you can use a different motor controller
rather than a different motor to jog to position. Simple proportional
feedback control should be plenty.
Feedback control also eliminates the problem with the clutch in your
stepper motor solution. In that case, you don't need full position
feedback, just a registration mark. If you know 1 fixed point on the
centrifuge, you know how many steps to your final position.
For that matter it just occured to me that if your timming belt is a 1:1
drive, you can make a clutch that stays in register. Think of the clutch
being two disks, 1 drive, 1 driven. The drive disk has 2 pins, 1 pin on
each of two center distances. The driven disk has matching holes. As the
drive disk pins slide into the driven disk, it always registers. That
means it is also registered with the centrifuge.
--
-------
Charly Coughran
ccoughran@DELETE-TO-RESPOND-UCSD.EDU |
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Tom Sanderson
science forum addict
Joined: 22 Dec 2005
Posts: 55
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| Posted: Tue May 23, 2006 4:02 pm Post subject:
Re: non-continuous torque transmission
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"shantia" <amin.zaribaf@gmail.com> wrote:
| Quote: | the idea is to cut the torque transmission to the stepper when main
high speed motor is running . but clatch is not acceptable because of
the slipage in clatch that will destroy the accuracy we need.
anybody has any practical Idea or some similar experiences?
|
One option is the type of mechanism used to connect a starter motor to the
flywheel in a car, but instead of using a spring to engage the gear, you can
use a solenoid. That way the stepper is geared to the main shaft when it's
running, but isn't connected when the solenoid is off and you can let the
high-speed motor do its thing.
There are also very good one-way clutches used in automatic transmissions,
the backlash is functionally zero, so unless you're positioning accuracy
needs to be extremely high I don't see why you can't just use that. When
the main motor is off and the stepper turns the one-way clutch, it will
rotate the shaft. When the main motor is on the one-way will slip and the
stepper won't turn.
Tom. |
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