How to Connect an LP-Research IMU to ROS (UPDATE)

This article describes how to connect an LP-RESEARCH inertial measurement unit (IMU) using a Robot Operating System (ROS) node. We are happy to announce that our IMU ROS sensor driver has been accepted into the official ROS package repository. The Robot Operating System, or ROS in short, is an open-source de-facto standard for robotics sensing and control. With the package openzen_sensor now provided as part of the ROS distribution Melodic Morenia it just became a whole lot easier to use our sensors in robotic applications.

Installation of IMU ROS Driver

All that’s needed is to install the package openzen_sensor via the distribution’s package manager. In Ubuntu, with the ROS Melodic Morenia distribution installed, use the following command:

Once the IMU ROS driver package is installed, we use the following command to start the OpenZen node:

This will automatically connect to the first available IMU and start streaming its accelerometer, gyroscope and magnetometer data to ROS. If your sensor is equipped with a GPS unit, global positioning information will also be transferred to ROS.

Once a sensor has been connected via the motion sensor driver, the data from the sensor is exported via ROS topics which can be consumed by other ROS components. This is for example a navigation and path planning system.

Published ROS Driver data topics

These are the ROS topics which get published by the OpenZen ROS driver:

Message Type Description
/imu/data sensor_msgs/Imu Inertial data from the IMU. Includes calibrated acceleration, calibrated angular rates and orientation. The orientation is always unit quaternion.
/imu/mag sensor_msgs/MagneticField Magnetometer reading from the sensor.
/imu/nav sensor_msgs/NavSatFix Global position from a satellite navigation system. Only available if the IMU includes a GNSS chip.
/imu/is_autocalibration_active std_msgs/Bool Latched topic indicating if the gyro autocalibration feature is active

Outputting IMU sensor values on the command line can now be easily done with:

and the data can be plotted with:

More information on the usage of the OpenZen IMU ROS driver can be found here.

The image above shows an angular velocity output graph in the ROS MatPlot application from an LPMS-IG1 sensor.

Robot Operating System and LP-Research IMUs? Simple!

Update: This is outdated. For new projects please consider using the openzen_sensor package which is distributed with ROS Melodic.

Robot Operating System (ROS) is a tool commonly used in the robotics community to pass data between various subsystems of a robot setup. We at LP-Research are also using it in various projects, and it is actually very familiar to our founders from the time of their PhDs. Inertial Measurement Units are not only a standard tool in robotics, the modern MEMS devices that we are using in our LPMS product line are actually the result of robotics research. So it seemed kind of odd that an important application case for our IMUs was not covered by our LpSensor software: namely, we didn’t provide a ROS driver.  We are very happy to tell you that such a driver exists, and we are happy that we don’t have to write it ourselves: the Larics laboratory at the University of Zagreb are avid users of both ROS and our LPMS-U2 sensors. So, naturally, they developed a ROS driver which they provide on their github site.  Recently, I had a chance to play with it, and the purpose of this blog post is to share my experiences with you, in order to get you started with ROS and LPMS sensors on your Ubuntu Linux system.

Installing the LpSensor Library

Please check our download page for the latest version of the library, at the time of this writing it is 1.3.5. I downloaded it, and then followed these steps to unpack and install it:

I also installed libbluettoth-dev, because without Bluetooth support, my LPMS-B2 would be fairly useless.

Setting up ROS and a catkin Work Space

If you don’t already have a working ROS installation, follow the ROS Installation Instructions to get started. If you already have a catkin work space you can of course skip this step, and substitute your own in what follows.  The work space is created as follows, note that you run catkin_init_workspace inside the src sub-directory of your work space.

Downloading and Compiling the ROS Driver for LPMS IMUs

We can now download the driver sources from github. It optionally makes use of and additional ROS module by the Larics laboratory which synchronizes time stamps between ROS and the IMU data stream.  Therefore, we have to clone two git repositories to obtain all prerequisites for building the driver.

That’s it, we are now ready to run catkin_make to get everything compiled and ready.  Building was as simple as running catkin_make, but you should setup the ROS environment before that.  If you haven’t, here’s how to do that:

This should go smoothly. Time for a test.

Not as Cool as LpmsControl, but Very Cool!

Now that we are set up, we can harness all of the power and flexibility of ROS. I’ll simply show you how to visualize the data using standard ROS tools without any further programming.  You will need two virtual terminals.  In the first start roscore, if you don’t have it running yet.  In the second, we start rqt_plot in order to see the data from our IMU, and the lpms_imu_node which provides it.  In the box you can see the command I use to connect to my IMU. You will have to replace the _sensor_model and _port strings with the values corresponding to your device.  Maybe it’s worth pointing out that the second parameter is called _port, because for a USB device it would correspond to its virtual serial port (typically /dev/ttyUSB0).

Once you enter these commands, you will then see the familiar startup messages of LpSensor as in the screenshot below. As you can see the driver connected to my LPMS-B2 IMU right away. If you cannot connect, maybe Bluetooth is turned off or you didn’t enter the information needed to connect to your IMU.  Once you have verified the parameters, you can store them in your launch file or adapt the source code accordingly.

Screenshot starting LPMS ROS node

Screenshot of starting the LPMS ROS node

The lpms_imu_node uses the standard IMU and magnetic field message types provided by ROS, and it publishes them on the imu topic.  That’s all we need to actually visualize the data in realtime.  Below you can see how easy that is in rqt_plot. Not as cool as LpmsControl, but still fairly cool. Can you guess how I moved my IMU?

animation of how to display LPMS sensor data in ROS

Please get in touch with us, if you have any questions, or if you found this useful for your own projects.

Update: Martin Günther from the German Research Center for Artificial Intelligence was kind enough to teach me how to pass ROS parameters on the command line.  I’ve updated the post accordingly.