Origin search - different position

[pszczepan 2]

Hi

I have servo motor controlled by smartstep 2 and controlled by PLC with pulse output.

Origin search I have set as below

Sometimes I have problem with correct home position. Normally when original Input signals become ON drive slows and after 1 cm I have home position due to slowning ramp, but somtimes drive stops immediately on the edge of original input sensor.

I have no idea why it is like that. Maybe you can advise sth or get some clue

thanks

in advance for any help

[pturmel 157]

Use a two-phase homing operation.  Typically high speed to make the signal, then very low speed in the other direction until it turns back off.  That makes the process insensitive to initial search deceleration.

[pszczepan 2]

What do you mean two-phase homing operation. I connected smartstep2 and PLC as it is in manual W450-E1-02  - page 232.

I have 2 more axles in this project with smaller motors 400W and there I don't have any problem with home position - similar origin search method. Some speeds only are different

 

[BobLfoot 301]

3 hours ago, pszczepan said:

What do you mean two-phase homing operation. I connected smartstep2 and PLC as it is in manual W450-E1-02  - page 232.

 

i dont have the manual or a lot of omron servo experience, but the detection method drop down currently is method 1.  I'll wager one of the other methods does the find marker , lose marker homing that @pturmel  suggested.  And you will find that more accurate and repeatable.

[pszczepan 2]

I used method 2, because I wanted to have better accuracy as you see below

Now you suggest to change to method 1. - OK, I can do that, but why manual say sth. different?

 

 

[pturmel 157]

Apparently, the homing method I described is not available.  Unless there are more than those three methods.  Method 2 as described appears to require two separate signals--one to slow down and the other to finish.  It is possible to scramble the result if the origin signal is already on when starting the search.  But otherwise, the origin signal and position complete signal must be far enough apart to ensure the latter can only come on when the motion is slow.

If there really isn't a way to change direction for the second phase of homing, using the one signal, I would avoid this drive like the plague.

[pszczepan 2]

Maybe you are right, I am not very familiar with that. From page 254 mentioned manual there are descriptions of each searching method, but for me it is hard to choose the most accurate. Maybe someone who uses Omron and these searching method can write sth from his practice?

[BobLfoot 301]

Can you provide a link for the manual?

Or at least the pages about Detection Method, not just Mode.

[pszczepan 2]

This is a link

https://assets.omron.eu/downloads/manual/en/v1/w450_cp1h_cpu_unit_operation_manual_en.pdf

 

and origin search starts from page 256 (pdf 290).

 

Thanks for your time

[BobLfoot 301]

I am not an omron expert, but reading page 258 of the manual I propose the following:

You have two signals at play here - "Origin Proximity Input" and "Origin Input".

Using Detection Method 1 your system does the follwoing:

1) Moves at High Speed

2) Sees the "Origin Proximity Input"

3) Slows Down to Search Speed

4) Sees the "Origin Input"

5) Stops.

What I suspect is happening is your two sensors are close together and some times the system see the "Origin Input" at the same instance as the "Origin Proximity"

I would physically seperate the two sensor flags if practical and look for things to change.

@pturmel  Tell me I'm not all wet here.

[pturmel 157]

1 hour ago, BobLfoot said:

Tell me I'm not all wet here.

Heh.  I didn't read the manual.  What you describe is not only plausible, but seems likely to me.

[lostcontrol 23]

@pturmel,

the functions used are PLC config, not the drive.

These applications need to be connected exactly as per the manual to work. It is possible that this is not the case for the OP.

 

If it were me, I’d be rolling my own code based on what is actually installed. All that is needed is a home sensor .

[pszczepan 2]

Yes I have 2 input signals, but "origin input" comes from Servomotor encoder's and it is phase-Z input; I cannot change physically any distance between origin proximity and origin input or I don't know how to do that.

 

 

Edited 18 Dec 2022 by pszczepan

[pturmel 157]

You will have to make mechanical changes to shaft angles.  This can involve significant mechanical rework of the servo mount or gearbox or coarse origin sensor position or all of the above.I recommend ensuring ½ to ¾ turn is clear between the edge of the coarse position sensor and the motor Z pulse.