XML-RPC

With XML-RPC, a program that runs on a Universal Robots cobot calls a function of your application and uses its answer: a position computed by a vision system, a number, a text. This page shows how to answer these calls with the SDK. The SDK is the server: it listens on a port of the PC, 50000 by default.

How it works

1. The robot program creates a connection to the PC with rpc_factory.
2. It calls a function of this connection. The robot waits for the answer.
3. The SDK raises XmlRpcServerRequest with the name of the function and its arguments. Your code sets Answer.
4. The robot assigns the answer to its variable, and the program continues.

URScript of the robot, where 192.168.0.10 is the address of the PC:

rpc := rpc_factory("xmlrpc", "http://192.168.0.10:50000")

pose := rpc.get_pose()
text := rpc.say_hello("UR5e")
total := rpc.sum([1, 3.5, -2])

See XML-RPC communication by Universal Robots. The address of the PC on the network of the robot is also in robot.PrimaryInterface.LocalEndPoint.

Example

The XML-RPC server is disabled by default: set XmlRpc.Enable in ConnectParameters.

static void Main(string[] args)
{
  var robot = new UR();

  var parameters = new ConnectParameters("192.168.0.1");

  // The XML-RPC server is disabled by default
  parameters.XmlRpc.Enable = true;
  parameters.XmlRpc.Port = 50000;

  robot.Connect(parameters);

  // Raised for each call of the robot program
  robot.XmlRpc.XmlRpcServerRequest += OnRequest;
  

// The robot program connects with:
//   rpc := rpc_factory("xmlrpc", "http://192.168.0.10:50000")
// where 192.168.0.10 is the address of this PC
static void OnRequest(object sender, XmlRpcEventArg request)
{
  Console.WriteLine(request.EndPoint.Address + " calls " + request.MethodName);

  switch (request.MethodName)
  {
    // URScript: answer := rpc.get_pose()
    case "get_pose":
      request.Answer = new Pose(0.4, -0.1, 0.3, 0, 3.14, 0); // m and rad
      break;

    // URScript: answer := rpc.say_hello("UR5e")
    case "say_hello":
      request.Answer = "Hello " + request.Arguments[0];
      break;

    // URScript: answer := rpc.sum([1, 3.5, -2])
    case "sum":
      double[] values = request.Arguments[0];
      request.Answer = values.Sum();
      break;

    // Without an answer, the variable of the robot is not assigned
    default:
      break;
  }
}
}

The same server works without UR:

static void Main(string[] args)
{
// An XML-RPC server, without a UR instance
var server = new XmlRpcServer();

server.XmlRpcServerRequest += (sender, request) =>
{
  if (request.MethodName == "get_counter")
    request.Answer = 42;
};

server.Start(50000);

// ...

server.Stop();
}
}

Allow the port of the server in the firewall of the PC.

Values

Answer and Arguments are XmlRpcValue. In C#, implicit conversions accept and return the native types: request.Answer = 12, = 3.5, = true, = "text", = new Pose(...), = new double[] {...}, and double[] values = request.Arguments[0].

A value that the SDK cannot read is an XmlRpcUnknownValue: its AdditionalInformation says why.

Without an answer, the function returns nothing to the robot and its variable is not assigned.

Example programs

PolyScope

xml_rpc_sample.urp calls several functions. The demo application shows each call and lets you choose the answer.

LabVIEW

The LabVIEW example answers GetPose() with the position of its front panel, and a text to the other functions:

Try it in the demo application

Everything on this page can be tried without writing code, in the Remote procedure call (XML-RPC) page of the demo application.

The demo application is open source. The C# source of this page is XmlRpcControl.cs.

Reference

What to read next

• Socket communication: exchange your own messages with the robot program.
• Read and write registers: exchange numbers with the robot program, without waiting.