From the help: Tuning rule for position lag error tolerance
The position lag error tolerance is not permitted to be higher than half of one pole length!
It refer to mechanical pole length or electrical pole length?
can anyone from BRCommunity help @Swee_Hoe ?
Hello,
i don’t understand the difference between electrical and mechanical pole length. I thought there is only one pole length.
As its a safety related question i am a bit careful…
Greetings
Michael
the electrical angle always equals 180 degree. If the max limit refer to electrical way of view, it will be always 90 degree.
Hello,
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I think the documented limit has something to do with the fact how far a motor will move if the IGBT gets defective. In this case a phase can be powered by this failure and move the motor. This movement would be dependend by the mechanical pole lenght.
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Also the mechanical pole lenght is dependend on the motor and is not a fixed value, so they could only refer to it by its name. If the electrical pole length is a fix 180° (never heard of this - learned somethink new
) i think they would have used this fix value in documentation. -
The mechanical pole lenght is typicaly also the smaller value.
I would go with mechanical pole lenght.
Greetings
Michael
From my understanding
You have a motor with pp polepairs (that’s what B&R motors use). So you have pp*2 poles. 360° / (pp*2) will be the length of one pole and thus 360° / (pp*2) / 2 will be half of that.. The position lag refers to your mechanical postion and thus for example if you have 360 units per rev, the lag error may not exceed 360/(pp*2)/2 units to not exceed one half pole
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Thanks for the comments.
I’m even more confused when I saw this:
https://help.br-automation.com/#/en/6/safety/safety_hardware/safemotion/ms-safety/geberanbau_ohne_nachweis.html
An electrical offset of <90° will not be detected sufficiently
But it follow by:
Note that an error can result in a forward movement. The maximum angle of rotation φ of the motor shaft during this forward movement depends on the motor being used.
For permanent magnet synchronous motors, φ = 360°/2p. For three-phase induction motors, there is a relatively small angle of rotation between 5° and 15°.
Above info seem like just want to tell us that the unavoidable movement angle will be 360/2p if servo is used. And it is mechanical pole pitch.
I think to detect shaft breakage, it should be more than mechanical pitch or else it detect error movement by nature of the motor.
I’m posting this to check check any proper way to determine this parameter. From the same doc, I can see:
In order to check the plausibility of setpoint selection after each power on, the axis must be moved by at least twice the configured lag error limit before the first request of a safety function, which requires a safe encoder evaluation, or at least within 15 min.
If this is not done, then the SafeMOTION module changes to the acknowledgeable FUNCTIONAL FAIL SAFE error state. Output “S_NotErrFUNC” of the function block is reset, and the drive loses all torque/power and coasts to a stop!
In the event of an error, a synchronous axis will no longer be synchronous.
I’m using B&R motor and unfortunately one of my colleague has this problem.
Hello;
SafeMOTION Anwenderhandbuch | B&R Industrial Automation
Page 751 English Version
This chapter explains the reachable Safety Functions due to the B&R Encoder Ordernumber, which is part of the Motor Ordernumber.
For all Encoders marked with the 1) it is required to use the supervison of shaft.
For all Encoders without this marking no supervision is needed.
The SafeMC functions can detect the mounting via a ParID 652: Motor: Encoder: Attribute (Default Setting)
It can be overwritten by the SafeMC Application, inside Safe Designer.
If supervision for shaft is enabled you have to:
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release the STO of the motor.
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move the motor by an larger amount that 2 times lagerror in less then 15 mins
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then you can use all the other Safety Function like SLS …
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The machine must move the axis every 24h , if no movement occurs an error will be set.
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If an error occured it can be reset and you can start from 1.
This sequence an only be used if there is a close enhousing available, to ensure that while only STO is released no user can reach dangerous movement parts.
If no enhousing is available you can switch to a motor with proof of mounting.
Greetings
Michael
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Thanks for the valuable info.
This mean I can safely disabled “Encoder monitoring - Posi-
tion setpoint alive testing (SPA) - Enable”? I’m using “DB” encoder and parid 652 show “1”.
From what I test on motor, it can’t be disable unless you use “approved by user”:
For B&R motors, the status of the fatigue strength of the encoder mounting is saved in the motor data
record.
But B&R manual told us to use “From motor data record”.
Hello,
Yes you can disable it.
This is the location where the SafeMC is deciding where to get the info of the Encoder Mounting.
If the SafeMC thinks he needs it there is an error upcoming.
I had this in case 652 is 0 and the Encoder Testing is disabled.
Greetings
Michael
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Hello,
The selection Approved by user is made for 3rd Party Motors where the ParID can’t be read from the motor, or for older B&R Motors which does not have these ParIDs.
In case you select Approved by user you have to make some note in your Safety Documentation which states, why you were alowed to select this setting and force the system to “know” that the motor has safety-Encoder Mouting.
Greetings
Michael