[etherlab-users] Omron Servo Drive with Distributed Clocks

[Henry Bausley]

When using an Omron Servo Drive we are getting synchronization errors
reported from the drive . 

Our code is bascially the dc_rtai example with the API rtos being a
little different.  We use xenomai and use a PowerPC 1Ghz w/ RTL8168
etherlabmaster 1.5 and operate based upon a H/W interrupt from a clock
that can have see ~20usec of worse case jitter.  Omron in Japan
currently has the drive what they report is as follows.



-------- Forwarded Message --------
From: Satoshi.Kuramoto at omron.com
To: Henry Bausley <hbausley at deltatau.com>
Subject: Re: Fw: ECAT testing between PMAC and G5
Date: Wed, 29 Feb 2012 16:48:40 -0800

Henry san, 

I am sorry to keep you waiting. 

I and Nakashima-san tested the EtherCAT connectivity between OMRON
servos and some EtherCAT masters including the latest PMAC. 
Unfortunately only PMAC had communication error. 

The reason would be that PMAC has the inaccurate timing in EtherCAT
frames,  compared to the other masters. 
OMRON servo, which equips 1 buffer , can not accept the inaccurate
timing of the master frames. 

<Test result between PMAC and OMRON servos> 

WKC=2 was confirmed under the condition of the LRW , so Write was
completed successfully but Read error occurred. 
This means writing MPU ->ASIC was not completed during read instruction
from the master. 

Normally there has to be timing gaps between a master and slaves, but
the EtherCAT master has functions to compensate the timing  by checking
into the timing of a slave. 
By utilizing this function, Acontis , Beckhoff , and OMRON can realize
the synchronous communication with OMRON servos. 
PMAC also has this function , but it seems not to work well. 

When PMAC is connected to Yaskawa and Sanmotion who have 3 buffers, no
communication error will exist. 
However 1 buffer slaves like OMRON showed the communication error,
because of smaller margins of the inaccuracy of frame timing. 

The reason for OMRON to have the 1 buffer is to realize higher accurate
synchronous control than 3 buffer.

------------------------


We have used Control Techniques, Sanmotion , Yaskawa, Kollmorgen , ABB,
Copley w/ DC without any issues.  

Does any one have any ideas for either proving or disproving Omron's
theory so we find a solution?




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