On 3/31/2012 1:43 PM, Peter C. Wallace wrote:
> On Sat, 31 Mar 2012, Dave wrote:
>
>
>> Date: Sat, 31 Mar 2012 14:20:19 -0500
>> From: Dave<e...@dc9.tzo.com>
>> Reply-To: "Enhanced Machine Controller (EMC)"
>> <emc-users@lists.sourceforge.net>
>> To: "Enhanced Machine Controller (EMC)"<emc-users@lists.sourceforge.net>
>> Subject: Re: [Emc-users] Trajectory planning and other topics from a,
>> EMC(LinuxCNC) newbie (TheNewbie)
>>
>> My experience with steppers is that once you lose sync with the rotor at
>> speed, you have to slow down tremendously to regain sync with the rotor.
>> So once you start slipping, you are pretty much done as you have lost
>> control of the motor. I don't see how using encoders with steppers
>> really helps other than detecting when you have lost control of the motor.
>>
>> Dave
>>
> If you have high res encoders and a high enough loop rate (say 30 -50 KHz) and
> a PWM sine/cos drive, you can run step motors as 50 pole 2 phase servos, they
> can never lose steps (as the drive phase is always synced to the rotor) and
> they have ~0 input power at ~0 load torque. However the driver circuits are
> more complicated than 3 phase PMS servo motors (4 1/2 bridges vs 3 1/2
> bridges) and you have still have the same torque/vs speed curve as with a
> normal step drive so unless you need something the the step motors provide
> (low speed torque maybe) step motors make fairly lousy servos
>
>
> Peter Wallace
> Mesa Electronics
>
> (\__/)
> (='.'=) This is Bunny. Copy and paste bunny into your
> (")_(") signature to help him gain world domination.
>
>
>>50 pole, 2 phase servos....
Interesting idea.
For low speed, low power positioning tasks that require high torque a
stepper is hard to beat $ wise and oftentimes doesn't need a gearbox and
can be self protecting - if it jams up, it slips, and nothing terrible
happens.
Dave
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