Hi,
It is any difference between using closed loop servo and STEP/DIR motion controller vs real close loop motion controller using encoder data from closed loop servo.
Thank you,
Coly
Hi,
It is any difference between using closed loop servo and STEP/DIR motion controller vs real close loop motion controller using encoder data from closed loop servo.
Thank you,
Coly
I assume you mean the difference where the encoder loop is returned to the trajectory planner and main controller rather than the final drive etc.
In this type, the controller is aware of what the servo's performance and actions are, as opposed to the type of control such as Mach that hands the motion control over to the drive where the encoder is returned to.
There are many advantages to the true closed loop, one features is electronic gearing and true synchronized threading for e.g., Another is if you initiate an E-stop and turn off the drives, you could conceivably move the motors/axis manually etc and on power up, the new position would be known.
and the control would not require re-referencing, these are just a couple.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
There are a couple of advantages of returning the position to the controller:
1. If the controller knows the actual position, it can monitor the actual following error (difference between commanded and actual position)
with a step/dir driver you only know the following error has not exceeded the drives preset limit (and maybe not even that)
2. If position is relayed to the controller the motor drive can be disabled (either by a fault or to allow hand movement) without losing position/requiring re-homing
3. Drives with multi-turn absolute encoders can relay absolute position information to the controller so no homing is needed at startup.
(same for absolute linear encoders)
4. In addition, drives that have full bidirectional communication to the host ( drives using various types of real time Ethernet for example)
allow the controller to monitor the drives torque and other drive parameters in real time for diagnostics and improved control
In most cases there is very little difference, I think you question is not quite correct
A servo and Drive close the loop can be driven many different ways + / - 10v Step / Dir Etc, the only difference when the loop is closed in the control ( much more complicated ) is the control is comparing the Encoder position to the coded position in the control
Just using the Servo Drive to close the loop, is doing the same thing, and just as accurate, and it compares the Encoder position to the commanded position from the same code the control put out
There are 2 types of servo drives, intelligent servo drives and dumb servo drives, so you have to decide, which you want to use Dumb servo Drive you have to close the loop in the control, intelligent Servo Drives you don't need to close the loop in the control, intelligent Servo Drives gives you the choice, you can close the loop either way
Encoder choice is very important, this will depend on what you want to control, if it is CNC equipment then you want nothing less than a 12 Bit encoder this is the minimum to use, I recommend 16Bit as a starting point
Mactec54
This in theory is correct, but in practice it is not, machines must be Homed even if they do have absolute Encoders, which most do have
I like your boards you make and the support you give with using them, but I think you are a little off track as saying there are advantages, modern Servo Drives can close the loop and feed back the position to the control if needed, which is less complicated to do if you want to track the following error, and adjust or auto correct it, they can do any of the other functions as well like torque control Etc.
As I said in my first post if you have dumb Servo Drives then you need to close the loop in the control, if you have intelligent Servo Drives it is not needed to close the loop in the control
Mactec54
Lot of info here.
Thank you!
I ask because I have samsung CSDJ drivers, I don't know if it is dumb or intelligent, and I am lucking for the motion controller.
Coly
They are intelligent digital servo drives, they can close the loop, and do most of what has been posted, so if you want a simple setup, ( Mach3 or UCCNC Etc. can be used for your control, your control does not need to no what the drive is doing, in simple terms, these drives will do it all, not the best choice because of the low Encoder count, but a very good Servo Drive
Mactec54
No, you are confusing single turn absolute encoders (which do need homing) and are common on lots of cheaper drives
with multi-turn absolute encoders which do not need homing since they always report the absolute machine position.
I stand by my list of advantages of closed loop feedback to the controller vs step/dir drives with no feedback to the controller
I have retro fitted from using Fanuc and Mitsubishi to the Very nice Galil System servo cards which are PC or stand alone based, these are very close to the industrial versions, they use ±10vdc analogue control and economical non-intelligent drive can be used, essentially trans-conductance (torque mode) amplifiers, this makes it very simple to implement a system as all the tuning is in the controller.
The tuning is actually simpler as there is virtually no tuning to do in the drive and the (only) PID loop is closed to the controller.
If you want a system such as this there is the Dynomotion and Kanalog system see the forum here.
The advantages and features available by closing the loop in the controller out-ways the drive closing any loop by far.
Al.
.
.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
No not taking about single turn Absolute Encoders
It has nothing to do with the Encoder, you have not used any modern machines, if they loose power, or you turn them off, when powering up they auto Home, you have no choice, even with battery backup, which most have, for Absolute Encoders, they are only good for retaining the last position for up to 30min, there are a lot of Absolute Encoder that only have a capacitor for the back up power, once this drains then it does not know where it was at, so it is always a safe practice to Home any machine no matter what the Encoder is, there are some exceptions for machines which have/use different Homing system
Was not talking about just step / dir drives, intelligent drives do it all plus more, than what you had in your list, including control feed back, here is what some of the quality AC Servo Drives offer
Pulse / Analog / RS232
Modbus RTU RS485
EatherCat
Can
There are other control methods as well but not all are created equal, and easy to use / install, a snip below of EatherCat use, this and Modbus are widely used in the industry for CNC Machines, Robots Etc
There are no advantages when using these Servo Drives as they can communicate with the control, just as well or better, than the old out a date system you are talking about, it also uses a lot less electronics and wiring to do the same job
Adaptive Tuning on the fly
8 Bit and 12 Bit security for the transfer of signals
Mactec54
Correct, always look at the encoder count though, this is important as to how smooth your machine will run, ( without the jerk factor ) the higher the PPR the better, if you already have the drives and motors, then you can try what you have, they are not the easiest to setup, others have used them before so there should be information posted some where of there setup, they have software you can down load and connect to each servo drive to set it up, they also have auto tuning, you can use once you have setup the basic parameters
Mactec54
That appears to be a fairly small motor at 100w.
The 2048p encoder will give you 8192 pulse resolution when the customary quadrature x4 is used.
This should give ample positioning resolution AKA Least Input Increment, which can be calculated by the distance movement of the axis for one motor revolution divided by (2048x4) 8192.
That resolution should give perfectly satisfactory results.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.
I agree this is normal, nothing new about this,
Battery is not months, it's about 2 years on average, some even longer
I don't no of any Encoders that are using super capacitors, ( Do you ) that would make that claim, on average they only guarantee to retain position information for 30min
There is no such thing they don't need to be Homed, theory yes practice no, they all use homing no matter what the type of encoders they use, as I said most new machining centers you have no choice they auto Home at power up you can't stop them from doing this, whether they need it or not, it's hard coded into the machine startup, most tool changers don't use encoders, and have to be Homed, this is part of the machines Homing routine
Mactec54
Nope.
There have is several big brand manufacturer been more than ten year producing machines which do not need homing at all. Just turn machine on and wait it boot up and start machining. There is no need move axis at all, encoder or scale will send absolute machine position information to to controll whitout any need of movement.
Its realy nice in daily use, but when you lose parameters and setup information or need change encoder then it is not so simple to get all settings tuned up.
I have currently machine with siemens control with absolute encoders. There is no home switches installed at all.
There is only power cut off switches for mailfunction at end of each end off axis stroke. If there is no fault or mailfunction you can not get machine to move to to these limit swiches not even if you intrntionaly try.
Lähetetty minun B15 laitteesta Tapatalkilla
I think you miss understand, your machine is homing even though you don't know or see it move, yes there are a lot of machines / controls that do this, that don't have Home switches, it is in the posts above, the different methods machines use, Okuma being one of the best at doing this, and the first to ever use this technology to it fullest
What you are experiencing when you can't reach the hard limits /end of stroke, is called soft limits, all machines have this, even hobby home built machines, this can be setup in the software like Mach3 and UNCNC and most other Hobby control software
Which way is the best is up to the users thinking, physical homing, or moving the machine around, helps the machine move the lubrication around before you start to run, at high speed, Spindle run warmup cycle is a must on any machine, if you don't do this your machines life will be less, so over all you gain nothing from your machine having this type of technology, 3 Axes Homing only takes about 20 seconds , on an average size machine
Mactec54