Closed loop vs. stepper motors -advice sought
Posted by jappiemike
|
Re: Closed loop vs. stepper motors -advice sought November 08, 2015 04:07PM |
There is NO firmware (that I know of) out there that uses feedback loop
reading encoders for positioning.
Are you planning on writing custom firmware?
20 inch linear encoder with good accuracy --- big bucks
How fast is interface to encoder?
Rotary encoder on the timing belt?
reading encoders for positioning.
Are you planning on writing custom firmware?
20 inch linear encoder with good accuracy --- big bucks
How fast is interface to encoder?
Rotary encoder on the timing belt?
|
Re: Closed loop vs. stepper motors -advice sought November 09, 2015 07:44PM |
Jappiemike Stated "using linear encoders along the X and Y axis to give me the accuracy"
Servo motor with encoder just insures motor moves as commanded
NOT
the accuracy of an end effector driven by leadscrew or belt
It appeared to me that the linear encoder would be independent of drive
indicating where the end effector is located
motor driving until encoder reports location is attained.
Most stepper motor drivers (Easydriver) have DIR, Step, enable, MS1, MS2 (Microstep)
is a servo that much better?
Digital servo is given angle command and it goes to that angle
with accuracy of the measurement device in servo.
I'm confused?
Servo motor with encoder just insures motor moves as commanded
NOT
the accuracy of an end effector driven by leadscrew or belt
It appeared to me that the linear encoder would be independent of drive
indicating where the end effector is located
motor driving until encoder reports location is attained.
Most stepper motor drivers (Easydriver) have DIR, Step, enable, MS1, MS2 (Microstep)
is a servo that much better?
Digital servo is given angle command and it goes to that angle
with accuracy of the measurement device in servo.
I'm confused?
Quote
jappiemike
Hello gentlemen,
I have been thinking of my next Arduino/Mbed project and a 3d printer/router/SLS/powder printer seems the go. I've been thinking of building a 500mx500mm welded steel (50x25mm sections) bed machine and using linear encoders along the X and Y axis to give me the accuracy that C7 ballscrews apparently won't. When using encoders why do you use quadrature code when you already know the direction the bed is moving having started to drive the motor clockwise or anticlockwise? Would using smallish DC brushed or brushless, I haven't decided on the pros and cons yet, through a zero backlash worm drive to give the higher torque be the best way to go? Because of the size of the axis would a central driving structure with supported linear rails on the outer extremes be as good as 2 drive structures alongside the rails to combat racking? And finally if I do manage to close the loop can I use a timing belt instead of the ball screws, at the moment I'm not intending to cut anything stronger than wood so there shouldn't be too much of a problem with stretching the belts.
Cheers
Mike
|
Re: Closed loop vs. stepper motors -advice sought December 11, 2015 06:54PM |
Ben Weiss article interesting (a thesis)
and uses Stepper motor.
The link to specifics on encoder [objects.reprap.org] is BAD.
since he mentions "alignment of the optical strip. I use the optical strip from the same printer as the encoder, since the encoder is optimized for a certain stripe spacing."
Probably is Linear encoder
The full pdf version of his paper much better
Edited 1 time(s). Last edit at 12/11/2015 07:11PM by cozmicray.
and uses Stepper motor.
The link to specifics on encoder [objects.reprap.org] is BAD.
since he mentions "alignment of the optical strip. I use the optical strip from the same printer as the encoder, since the encoder is optimized for a certain stripe spacing."
Probably is Linear encoder
The full pdf version of his paper much better
Edited 1 time(s). Last edit at 12/11/2015 07:11PM by cozmicray.
|
Re: Closed loop vs. stepper motors -advice sought March 01, 2016 10:31AM |
Quote
the_digital_dentist
Can anyone tell me what benefit would come from replacing steppers with the complication and expense of servo motors?
Someone who can answer you, wouldn't envision the use of servo motors/encoders for such thing as a 3D FDM printer, wood working machine or similar requiring an accuracy of 1/10th, moderate speed, no massive parts to move !
Servos, encoders have been in use for 40 years now and yet, steppers are still used (some even fitted with encoders !) despite lower and integrated electronic cost. So ?
yes, servos electronic has moved from analog to digital, but the overall cost still remains high.
Funny but for minimal requirements, like to adjust the height of a car headlights, it is a done with a servo motor and not a stepper. Stepper seems to be squeezed between low end and high end
An other thing to consider, an MDF frame with shining Heidenhain encoders and ball lead screws, the warmth of wood, the glitter of gold and steel, is a thing a beauty isn't ?
Edited 1 time(s). Last edit at 03/01/2016 10:54AM by MKSA.
|
Re: Closed loop vs. stepper motors -advice sought March 01, 2016 11:00AM |
Quote
dc42
I think the main advantage of using servo-controlled motors to control the XYZ axes of a 3D printer instead of steppers would be that it would avoid the possibility of missed steps.
When I see how most machines are poorly assembled, lack rigidity, if not poorly designed, I bet most of the "missed steps" are due to bindings, parts seizing etc..., in addition of course to asking the stepper too much in term of speed, acceleration ...
With servos, the machine would probably explode
Edited 2 time(s). Last edit at 03/01/2016 11:02AM by MKSA.
Sorry, only registered users may post in this forum.