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Universal Robots Client Library

• Universal Robots Client Library
  • Requirements
  • Build instructions
    • Plain cmake
    • Inside a ROS workspace
  • Use this library in other projects
  • License
  • Library contents
  • Example driver
  • Architecture
    • RTDEClient
      • RTDEWriter
    • ReverseInterface
    • ScriptSender
    • Other public interface functions
      • check_calibration()
      • sendScript()
    • DashboardClient
  • A word on the primary / secondary interface
  • A word on Real-Time scheduling
  • Producer / Consumer architecture
  • Logging configuration
    • Change logging level
    • Create new log handler
    • Console_bridge
  • Acknowledgement

A C++ library for accessing Universal Robots interfaces. With this library C++-based drivers can be implemented in order to create external applications leveraging the versatility of Universal Robots robotic manipulators.

Requirements

• The library requires an implementation of POSIX threads such as the pthread library

• Socket communication is currently based on Linux sockets. Thus, this library will require Linux for building and using.

• The master branch of this repository requires a C++17-compatible compiler. For building this library without a C++17-requirement, please use the boost branch instead that requires the boost library. For the C++17 features, please use those minimum compiler versions:

  Compiler	min. version
  GCC	7
  Clang	7

Build instructions

Plain cmake

To build this library standalone so that you can build you own applications using this library, follow the usual cmake procedure:

cd <clone of this repository>
mkdir build && cd build
cmake ..
make
sudo make install

This will install the library into your system so that it can be used by other cmake projects directly.

Inside a ROS workspace

If you want to build this library inside a ROS workspace, e.g. because you want to build the Universal Robots ROS driver from source, you cannot use catkin_make directly, as this library is not a catkin package. Instead, you will have to use catkin_make_isolated or catkin build to build your workspace.

Use this library in other projects

When you want to use this library in other cmake projects, make sure to

• Add find_package(ur_client_library REQUIRED) to your CMakeLists.txt
• add ur_client_library::urcl to the list of target_link_libraries(...) commands inside your CMakeLists.txt file

As a minimal example, take the following "project":

/*main.cpp*/

#include <iostream>
#include <ur_client_library/ur/dashboard_client.h>

int main(int argc, char* argv[])
{
  urcl::DashboardClient my_client("192.168.56.101");
  bool connected = my_client.connect();
  if (connected)
  {
    std::string answer = my_client.sendAndReceive("PolyscopeVersion\n");
    std::cout << answer << std::endl;
    my_client.disconnect();
  }
  return 0;
}

# CMakeLists.txt

cmake_minimum_required(VERSION 3.0.2)
project(minimal_example)

find_package(ur_client_library REQUIRED)
add_executable(db_client main.cpp)
target_link_libraries(db_client ur_client_library::urcl)

License

The majority of this library is licensed under the Apache-2.0 licensed. However, certain parts are licensed under different licenses:

• The queue used inside the communication structures is originally written by Cameron Desrochers and is released under the BSD-2-Clause license.
• The semaphore implementation used inside the queue implementation is written by Jeff Preshing and licensed under the zlib license
• The Dockerfile used for the integration tests of this repository is originally written by Arran Hobson Sayers and released under the MIT license

While the main LICENSE file in this repository contains the Apache-2.0 license used for the majority of the work, the respective libraries of third-party components reside together with the code imported from those third parties.

Library contents

Currently, this library contains the following components:

• Basic primary interface: The primary interface isn't fully implemented at the current state and provides only basic functionality. See A word on the primary / secondary interface for further information about the primary interface.
• RTDE interface: The RTDE interface is fully supported by this library. See RTDEClient for further information on how to use this library as an RTDE client.
• Dashboard interface: The Dashboard server can be accessed directly from C++ through helper functions using this library.
• Custom motion streaming: This library was initially developed as part of the Universal Robots ROS driver. Therefore, it also contains a mechanism to do data streaming through a custom socket, e.g. to perform motion command streaming.

Example driver

In the examples subfolder you will find a minimal example of a running driver. It starts an instance of the UrDriver class and prints the RTDE values read from the controller. To run it make sure to

• have an instance of a robot controller / URSim running at the configured IP address (or adapt the address to your needs)
• run it from the package's main folder (the one where this README.md file is stored), as for simplicity reasons it doesn't use any sophisticated method to locate the required files.

Architecture

The image below shows a rough architecture overview that should help developers to use the different modules present in this library. Note that this is an incomplete view on the classes involved.

The core of this library is the UrDriver class which creates a fully functioning robot interface. For details on how to use it, please see the Example driver section.

The UrDriver's modules will be explained in the following.

RTDEClient

The RTDEClient class serves as a standalone RTDE client. To use the RTDE-Client, you'll have to initialize and start it separately:

rtde_interface::RTDEClient my_client(ROBOT_IP, notifier, OUTPUT_RECIPE, INPUT_RECIPE);
my_client.init();
my_client.start();
while (true)
{
  std::unique_ptr<rtde_interface::DataPackage> data_pkg = my_client.getDataPackage(READ_TIMEOUT);
  if (data_pkg)
  {
    std::cout << data_pkg->toString() << std::endl;
  }
}

Upon construction, two recipe files have to be given, one for the RTDE inputs, one for the RTDE outputs. Please refer to the RTDE guide on which elements are available.

Inside the RTDEclient data is received in a separate thread, parsed by the RTDEParser and added to a pipeline queue.

Right after calling my_client.start(), it should be made sure to read the buffer from the RTDEClient by calling getDataPackage() frequently. The Client's queue can only contain 1 item at a time, so a Pipeline producer overflowed! error will be raised if the buffer isn't read before the next package arrives.

For writing data to the RTDE interface, use the RTDEWriter member of the RTDEClient. It can be retrieved by calling getWriter() method. The RTDEWriter provides convenience methods to write all data available at the RTDE interface. Make sure that the required keys are configured inside the input recipe, as otherwise the send-methods will return false if the data field is not setup in the recipe.

An example of a standalone RTDE-client can be found in the examples subfolder. To run it make sure to

• have an instance of a robot controller / URSim running at the configured IP address (or adapt the address to your needs)
• run it from the package's main folder (the one where this README.md file is stored), as for simplicity reasons it doesn't use any sophisticated method to locate the required files.

RTDEWriter

The RTDEWriter class provides an interface to write data to the RTDE interface. Data fields that should be written have to be defined inside the INPUT_RECIPE as noted above.

The class offers specific methods for every RTDE input possible to write.

Data is sent asynchronously to the RTDE interface.

ReverseInterface

The ReverseInterface opens a TCP port on which a custom protocol is implemented between the robot and the control PC. The port can be specified in the class constructor.

It's basic functionality is to send a vector of floating point data together with a mode. It is meant to send joint positions or velocities together with a mode that tells the robot how to interpret those values (e.g. SERVOJ, SPEEDJ). Therefore, this interface can be used to do motion command streaming to the robot.

In order to use this class in an application together with a robot, make sure that a corresponding URScript is running on the robot that can interpret the commands sent. See this example script for reference.

Also see the ScriptSender for a way to define the corresponding URScript on the control PC and sending it to the robot upon request.

ScriptSender

The ScriptSender class opens a tcp socket on the remote PC whose single purpose it is to answer with a URScript code snippet on a "request_program" request. The script code itself has to be given to the class constructor.

Use this class in conjunction with the External Control URCap which will make the corresponding request when starting a program on the robot that contains the External Control program node. In order to work properly, make sure that the IP address and script sender port are configured correctly on the robot.

Other public interface functions

This section shall explain the public interface functions that haven't been covered above

check_calibration()

This function opens a connection to the primary interface where it will receive a calibration information as the first message. The checksum from this calibration info is compared to the one given to this function. Connection to the primary interface is dropped afterwards.

sendScript()

This function sends given URScript code directly to the secondary interface. The sendRobotProgram() function is a special case that will send the script code given in the RTDEClient constructor.

DashboardClient

The DashboardClient wraps the calls on the Dashboard server directly into C++ functions.

After connecting to the dashboard server by using the connect() function, dashboard calls can be sent using the sendAndReceive() function. Answers from the dashboard server will be returned as string from this function. If no answer is received, a UrException is thrown.

Note: In order to make this more useful developers are expected to wrap this bare interface into something that checks the returned string for something that is expected. See the DashboardClientROS as an example.

A word on the primary / secondary interface

Currently, this library doesn't support the primary interface very well, as the Universal Robots ROS driver was built mainly upon the RTDE interface. Therefore, there is also no PrimaryClient for directly accessing the primary interface. This may change in future, though.

The comm::URStream class can be used to open a connection to the primary / secondary interface and send data to it. The producer/consumer pipeline structure can also be used together with the primary / secondary interface. However, package parsing isn't implemented for most packages currently. See the primary_pipeline example on details how to set this up. Note that when running this example, most packages will just be printed as their raw byte streams in a hex notation, as they aren't implemented in the library, yet.

A word on Real-Time scheduling

As mentioned above, for a clean operation it is quite critical that arriving RTDE messages are read before the next message arrives. Due to this, both, the RTDE receive thread and the thread calling getDataPackage() should be scheduled with real-time priority. See this guide for details on how to set this up.

The RTDE receive thread will be scheduled to real-time priority automatically, if applicable. If this doesn't work, an error is raised at startup. The main thread calling getDataPackage should be scheduled to real-time priority by the application. See the ur_robot_driver as an example.

Producer / Consumer architecture

Communication with the primary / secondary and RTDE interfaces is designed to use a consumer/producer pattern. The Producer reads data from the socket whenever it comes in, parses the contents and stores the parsed packages into a pipeline queue. You can write your own consumers that use the packages coming from the producer. See the comm::ShellConsumer as an example.

Logging configuration

As this library was originally designed to be included into a ROS driver but also to be used as a standalone library, it uses custom logging macros instead of direct printf or std::cout statements.

The macro based interface is by default using the DefaultLogHandler to print the logging messages as printf statements. It is possible to define your own log handler to change the behavior, see create new log handler on how to.

Change logging level

Make sure to set the logging level in your application, as by default only messages of level WARNING or higher will be printed. See below for an example:

#include "ur_client_library/log.h"

int main(int argc, char* argv[])
{
  urcl::setLogLevel(urcl::LogLevel::DEBUG);

  URCL_LOG_DEBUG("Logging debug message");
  return 0;
}

Create new log handler

The logger comes with an interface LogHandler, which can be used to implement your own log handler for messages logged with this library. This can be done by inheriting from the LogHandler class.

If you want to create a new log handler in your application, you can use below example as inspiration:

#include "ur_client_library/log.h"
#include <iostream>

class MyLogHandler : public urcl::LogHandler
{
public:
  MyLogHandler() = default;

  void log(const char* file, int line, urcl::LogLevel loglevel, const char* log) override
  {
    switch (loglevel)
    {
      case urcl::LogLevel::INFO:
        std::cout << "INFO " << file << " " << line << ": " << log << std::endl;
        break;
      case urcl::LogLevel::DEBUG:
        std::cout << "DEBUG " << file << " " << line << ": " << log << std::endl;
        break;
      case urcl::LogLevel::WARN:
        std::cout << "WARN " << file << " " << line << ": " << log << std::endl;
        break;
      case urcl::LogLevel::ERROR:
        std::cout << "ERROR " << file << " " << line << ": " << log << std::endl;
        break;
      case urcl::LogLevel::FATAL:
        std::cout << "ERROR " << file << " " << line << ": " << log << std::endl;
        break;
      default:
        break;
    }
  }
};

int main(int argc, char* argv[])
{
  urcl::setLogLevel(urcl::LogLevel::DEBUG);
  std::unique_ptr<MyLogHandler> log_handler(new MyLogHandler);
  urcl::registerLogHandler(std::move(log_handler));

  URCL_LOG_DEBUG("logging debug message");
  URCL_LOG_INFO("logging info message");
  return 0;
}

Acknowledgment

Many parts of this library are forked from the ur_modern_driver.

Developed in collaboration between:

  and   .

Supported by ROSIN - ROS-Industrial Quality-Assured Robot Software Components. More information: rosin-project.eu

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 732287.