KUKA iiwa Digital I/O Error: Resolving Null IOGroup

A KUKA iiwa 14 R820 application can shut down when UDP communication code reads a media-flange I/O point through a null I/O-group object. The evidence-supported correction is to construct the MediaFlangeIOGroup during communicator setup and pass that same reference into UDPSender. Treat thread access as a separate, unconfirmed issue only if the failure remains.

Identify the null I/O-group failure

The pendant message establishes only that an object is null; it does not identify the object or prove that the requested I/O method is invalid. Check whether the complete I/O-group reference is null before investigating the individual pin-reading method. The reported application failed as soon as the I/O-reading line was enabled, making the I/O-group reference the first dependency to inspect.

Initialize and pass one MediaFlangeIOGroup reference

Create the media-flange I/O group in the main communicator setup, where the Sunrise cabinet reference is available:

MediaFlangeIOGroup iogrp = new MediaFlangeIOGroup(kuka_Sunrise_Cabinet_1);

Then accept that initialized object in the UDP sender constructor and assign it to the sender field:

public UDPSender(
    InetAddress externaladdress,
    int externalport,
    BlockingQueue<PRC_CommandData> UDPQueue,
    MediaFlangeIOGroup iogrp) throws SocketException {

    socket = new DatagramSocket(30001);
    address = externaladdress;
    port = externalport;
    CmdQueue = UDPQueue;
    flangeIO = iogrp;
}

Do not repeatedly recreate the group inside the sender loop with new MediaFlangeIOGroup(cabinet). The reported communicator began working after the I/O group was referenced during setup.

Transfer the I/O state in the UDP payload

The existing payload is a comma-separated string containing queue size, position, Cartesian data, and a force vector. If an I/O state replaces one of the force-vector values, serialize it as a numeric value rather than the strings TRUE or FALSE, then translate the received number back to a Boolean state in Grasshopper.

return new Integer(CmdQueue.size()).toString()
    + "," + posstr
    + "," + cartstr
    + "," + forcevector;

Verify the correction and isolate threading

1. Confirm that the communicator setup constructs the I/O group before creating UDPSender.
2. Step through the program and verify that iogrp at construction and flangeIO at the read operation are not null.
3. Run the UDP application and confirm that enabling the I/O-reading line no longer shuts it down.
4. Verify that Grasshopper receives the numeric state and converts it to the expected Boolean value.
5. If the reference is valid but the read still fails, move the same I/O operation into the main program. Success there but failure in the UDP thread indicates a possible thread-access limitation; the evidence does not confirm whether KUKA Sunrise I/O is thread-safe, so verify that behavior through official KUKA support.

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