Developing a robotic app
Developing a robotic app
(OP)
I am developing a robotic app which requires quick changes
in direction and speed.
For reliability, I want to avoid brushes and so it seems my
choice is either 3-phase induction (squirrel cage) or
brushless DC.
The app will require approximately 3/4hp & 0-2400rpm.
My power will be wall current (120V AC) and I will use a
microcontroller with appropriate inverter for either
approach. It would be great if the motor could reverse in
100-200ms. Position control does not need to be precise
so a stepper or servo (as I think is usually used for this
type of app) is not warranted.
Which motor type would be best for this? If both can
generally meet the performance requirements, does 3-phase
have a cost advantage over brushless DC?
Thanks,
dpenney
in direction and speed.
For reliability, I want to avoid brushes and so it seems my
choice is either 3-phase induction (squirrel cage) or
brushless DC.
The app will require approximately 3/4hp & 0-2400rpm.
My power will be wall current (120V AC) and I will use a
microcontroller with appropriate inverter for either
approach. It would be great if the motor could reverse in
100-200ms. Position control does not need to be precise
so a stepper or servo (as I think is usually used for this
type of app) is not warranted.
Which motor type would be best for this? If both can
generally meet the performance requirements, does 3-phase
have a cost advantage over brushless DC?
Thanks,
dpenney





RE: Developing a robotic app
RE: Developing a robotic app
Can you elaborate on why DC is better for this than 3-phase
AC (both are brushless)? Obviously, I would prefer to get
by with 3-phase AC if it were possible, for the lower cost.
RE: Developing a robotic app
RE: Developing a robotic app
The squirrel-cage induction motors are normally not designed for frequent reversals. It would need a heavy duty service inducton motor product. It is more expensive and heavier to dissipate the heat.
RE: Developing a robotic app
Rich Schmidt
RE: Developing a robotic app
Some more application detail would be nice.
ElMimino, sorry but I got a little laugh about your comment on making a rotary orientation linear induction motor. Isn't that just a regular AC Induction motor (or are you talking about a ring-track bearing and a round aluminum reaction plate?).
If you need too reverse cycles at a high frequency, then a mechanical system (as Steventyj was stating) may be the way to go - Crank or cam type sytem.
Cameron Anderson - Sales & Applications Engineer
Aerotech, Inc. - www.aerotech.com
"Dedicated to the Science of Motion"
RE: Developing a robotic app
dinasour types, but much faster moving) that is interactive.
So there may be slow movement in one direction, but then an
abrupt reverse and/or speed increase (or fast movement and
speed decrease), in response to some stimulus. Several
motors will be needed for several axis of motion and much of
the movement will be random, non-repetitive, controlled by
a PC.
So, does it still sound like I can get the performance I
need (at the lowest cost) with the 3-phase AC induction
motor (but heavy-duty type per jbartos input), using servo
control?
Thanks for all your responses.
RE: Developing a robotic app
RE: Developing a robotic app
RE: Developing a robotic app
As far as the reliability concerns, induction beat brushless DC motor. On the other hand, efficiency will be higher in brushless DC than in Induction motor which is an advantage in the long run.
One more thing I need to add is the physical size comparison. Brushless DC will be smaller than induction motor for the same power level.
RE: Developing a robotic app
Can an AC induction motor perform the same way?
Or does it require an impractical amount of current to do so?
automatic2- I considered a hydraulic system but decided to avoid it due to the high pressure required for the faster movements. Also, hydraulics are even farther out of my area of expertise!
If AC induction can't provide holding torque then I think I would sacrifice reliability and resort to using universal motors (brushed). But then I think there are additional problems from the high voltages of the quick direction changes, not to mention safety issues if it sparks.
moturcu - I would like to learn more on how to beat the heat problems by dynamic braking or regenerative operation. Can you point me to any web resources on it? Is it as simple as shunting the inductive kickback voltage into a capacitor?
I don't think the poorer efficiency and larger size of AC induction vs. BLDC is a problem for my app. Efficiency means less power required, and less heat, which is beneficial but I guess wouldn't outweigh the cost advantage. Any other efficiency implications?
Thanks,
dpenney
RE: Developing a robotic app
Whereas Dynamic brake approach is to connect proper resistance across DC bus during reversal.
Speed reversal takes place in two steps:decelaration and accelation to other direction. During decelaration stage, motor acts as generator, and pumps the energy to DC bus capacitor. This increases DC bus voltage. A simple controller, connects resistor during this high time of the DC bus to absorb energy and keep the voltage level constant.
Following web site may be helpful.
www.reliance.com/prodserv/standriv/appnotes/d7733.pdf
RE: Developing a robotic app
They make all types of motors, Brushless Servo, AC Induction, Regen, Open-Loop Vecotor, Closed-Loop Vector. Talk to one of their Applications Engineers and they can help you determine what control system will be best for your application.
If linear actuators can help do the movements, maybe even like through a Stewart Model, take a look at Exlar, www.exlar.com for Electro-Mechanical actuators.
Good Luck!
Cameron Anderson - Sales & Applications Engineer
Aerotech, Inc. - www.aerotech.com
"Dedicated to the Science of Motion"
RE: Developing a robotic app
RE: Developing a robotic app
RE: Developing a robotic app
RE: Developing a robotic app
http://www.hydrofloamerica.com/products/dcdrive.html
for an electronic overload protection in DC SCR Variable Speed Drive that prevents the permanent magnet motor demagnetization. If the electronic protection is somewhat off or malfunctions, the permanent magnet motor will eventually become demagnetized to a noticeable extent.
RE: Developing a robotic app
Current control is an inherent feature in a permanent magnet DC motor based system. Controller and current regulator will always make sure current will not exceed certain prescribed level while they shape the current as sinusoidal or trapezoidal. So we should not worry about the demagnetization as long as current regulator is there.