self-developed UDP server can receive xml file from robot, but cannot send xml successfully

Dear all,

My robot is kuka KR6-R900, with KRC4 compact and KSS 8.6.6. The version of RSI is 4.0.

I am trying to connect an external PC to my robot to achieve real time motion control. Right now I am basically following the RSI_Ethernet example in the manual while I developed a UDP server in Python 3.9 to imitate the function of Testserver.exe.

Testing with Testserver.exe is good, I am able to acquire signal and command movement. However, using my own UDP server, I am able to receive xml message from robot but send command to robot. So I guess the ethernet configuration and UDP connection are alright. What happens is RSI will stop in few seconds after the execution of "RSI_MOVECORR()", and pops out "stop by $CORRECTION function (reset or block selection required)" and "Signal flow (running): Object ETHERNET 1 returns error RSITimeout". Meanwhile my UDP server will terminate after receiving several xml message from robot.

I guess the possible cause is either the robot address is set wrong in my UDP server, or the XML format is incorrect. I put effort on checking everything but haven't sort this problem out yet. Any advice from you is appreciated!

My Ethernet configuration:

robot side:

IP: 192.168.1.2 (RSI, virtual 6)

subnet: 255.255.255.0

(I forget other settings but they are default)

external PC side:

IP 192.168.1.1

submnet prefix length 24

gateway 192.168.1.2

DNS 8.8.8.8/ 8.8.4.4

XML message from robot:

<Rob Type="KUKA">
<RIst X="445.0" Y="0.0" Z="790.0" A="180.0" B="0.0" C="180.0"/>
<RSol X="445.0" Y="0.0" Z="790.0" A="180.0" B="0.0" C="180.0"/>
<Delay D="0"/>
<Tech C11="0.0" C12="0.0" C13="0.0" C14="0.0" C15="0.0" C16="0.0"  C17="0.0" C18="0.0" C19="0.0" C110="0.0"/>
<DiL>0</DiL><Digout o1="0" o2="0" o3="0"/>
<Source1>0.0</Source1>
<IPOC>29106442</IPOC>
</Rob>

XML message sent to robot from external PC:

<Sen Type="ImFree">
<EStr>Message from RSI TestServer</EStr>
<Tech T21="1.09" T22="2.08" T23="3.07" T24="4.06" T25="5.05" T26="6.04" T27="7.03" T28="8.02" T29="9.01" T210="10.00" />
<RKorr X="0.000" Y="1.0000" Z="0.0000" A="0.0000" B="0.0000" C="0.0000" />
<DiO>125</DiO>
<IPOC>53189046</IPOC>
</Sen>

UDP server code (Python 3.9):

import socket
import os
import time
import xml.etree.ElementTree as ET


# bind UDP socket
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

#my local IP of external PC is set to 192.168.1.1, same as defined in RSI_Config.xml
# submnet prefix length 24, gateway 192.168.1.2, DNS 8.8.8.8/ 8.8.4.4
server_addr = ('192.168.1.1',59152)
s.bind(server_addr)
print('Bind UDP on 59152...')

# count bytes
cnt=0

while True:
    #receive xml file from robot
    data, client_addr = s.recvfrom(1024)

    # record initial IPOC number from robot
    if cnt==0:
        
        #record received xml from robot into a file
        f = open("input1.xml", 'wb')
        f.write(data)
        f.close()

        # find IPOC tag
        input = ET.parse("input1.xml")
        in_root = input.getroot()

        # get IPOC value
        for ipoc in in_root.iter('IPOC'):
            timestamp=ipoc.text
        print(timestamp)
        timestamp=str(int(timestamp)+4+cnt*4)
        print(timestamp)

        # prepare xml sent from extenal PC to robot
        output=ET.parse('output.xml')
        out_root=output.getroot()

        # change IPOC in output xml
        for ipoc in out_root.iter('IPOC'):
            ipoc.text=timestamp
        output.write('output1.xml')

        #send prepared xml file 
        filename = "output1.xml"
        J = open(filename,'rb')
        client_addr = ('192.168.1.2',59152)
        data = J.read(1024)
        s.sendto(data,client_addr)

    # starting from the second file received from robot, no longer record xml file
    # only calculate timestamp at interval of 4ms
    else:
        print(cnt)
        timestamp=str(int(timestamp)+4+cnt*4)

        # prepare xml sent from extenal PC to robot
        output=ET.parse('output.xml')
        out_root=output.getroot()

        # change IPOC in output xml
        for ipoc in out_root.iter('IPOC'):
            ipoc.text=timestamp
        output.write('output1.xml')

        #send prepared xml file 
        filename = "output1.xml"
        J = open(filename,'rb')
        client_addr = ('192.168.1.2',59152)
        data = J.read(1024)
        s.sendto(data,client_addr)


    cnt=cnt+1

Quote from huythai

Hi Wong!

I also did a similar project as you are doing but with C# language (So I can not consult you with PYTHON :D)

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I would recommend you first to use Hercules as an intermediate level to check for both connections from the robot and PC, not directly from the PC-python app to robot RSI because It would be difficult for debugging

Next, just make sure the network transmission frames are in order of receiver and sender sockets (an example is in the picture)

Hope it helps.

BR,

Quang Huy

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Hi Quang,

Thank you so much for your advice. I was really inspired that there is a software to check connection detail. Finally I make my own program working!

Your project looks quiet fun, what's that for? Using joystick to control robot?

bests,

Arthur Wong

Quote from SkyeFire

For any RSI project, adding a Monitor object and capturing the data from inside RSI is crucial to debugging.

I would recommend using WireShark or something similar to check exactly what is being sent to the robot. Tiny formatting errors can be fatal.

Before attempting motion control, I would suggest trying an RSI program that just receives some data from your server and echoes it back. Isolate the motion issue from the communications issue.

Hi Skyfire,

Thank you so much for your advice, they are really helpful. Using wireshark I am able to analyze what is the exact process of UDP communication. Finally I got me bugs fixed, now my server can be used to control robot! Appreicate it!

bests,

Arthur Wong

For anyone who may face the same issue as mine, I would like to summarize my mistakes for your information:

Regarding the error "Signal flow (running): Object ETHERNET 1 returns error RSITimeout" there are two causes, one is the Ethernet communication isn't set up correctly, the other is the IPOC tag.

1. Port number: I used the same port number for server and message sent to client (robot) by the server, which is wrong. The port number of client can be defined, but in this case it is automatically allocated by robot itself, and it is not 59152. A naive mistake.

2. IPOC: I guess this IPOC tag in xml file is used as timestamp. In the packets back and forward between example Testserver.exe and robot, they have the same IPOC number. (I guess) With some level of tolerance, a same IPOC number should be sent back to robot within 100 cycles, otherwise this RSI timeout error happens.

3. xml.etree.ElementTree: the functions from this library needs some time to execute, be caution of timing.

and the following is my UDP server code:

import socket
import os
import time
import xml.etree.ElementTree as ET
count = 0
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
server_addr = ('192.168.1.1',59152)
s.bind(server_addr)

print('Bind UDP on 59152...')
cnt=0
timestamp=0
output='<Sen Type="ImFree"><EStr>Message from RSI TestServer</EStr><Tech T21="1.09" T22="2.08" T23="3.07" T24="4.06" T25="5.05" T26="6.04" T27="7.03" T28="8.02" T29="9.01" T210="10.00" /><RKorr X="0.000" Y="1.0000" Z="0.0000" A="0.0000" B="0.0000" C="0.0000" /><DiO>125</DiO><IPOC>'+str(timestamp)+'</IPOC></Sen>'
while True:
    data, client_addr = s.recvfrom(1024)
    if cnt==0:
        
        f = open("input1.xml", 'wb')
        f.write(data)
        f.close()
        input = ET.parse("input1.xml")
        in_root = input.getroot()
        for ipoc in in_root.iter('IPOC'):
            timestamp=ipoc.text
    else: 
        timestamp=str(int(timestamp)+4)
        output='<Sen Type="ImFree"><EStr>Message from RSI TestServer</EStr><Tech T21="1.09" T22="2.08" T23="3.07" T24="4.06" T25="5.05" T26="6.04" T27="7.03" T28="8.02" T29="9.01" T210="10.00" /><RKorr X="0.000" Y="0.0000" Z="0.0000" A="0.0000" B="0.0100" C="0.0000" /><DiO>125</DiO><IPOC>'+str(timestamp)+'</IPOC></Sen>'
    cnt=cnt+1
    print(client_addr)
    s.sendto(output.encode(),client_addr)