Intégration de 4 robots mobiles omnidirectionnels avec des bras collaboratifs sur colonne télescopique pour l’université de Fribourg

Integration of 4 cobots setup on a telescopic column, mounted on omnidirectional mobile robots

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Context: An experiment on robots helping out with household chores

Assistant robots designed to help with household chores (especially for the elderly or people with reduced mobility) is an issue that many researchers are working on.

Toyota, Preferred Networks, MIT, Sony and Carnegie Mellon University are all doing work in this particular area.

A robot that can identify and put away items lying around on the floor. A window cleaning robot, a robot that irons or cooks…

Intégration de 4 robots mobiles omnidirectionnels avec des bras collaboratifs sur colonne télescopique

It is in this context that the University of Freiburg
(Albert-Ludwigs-Universität Freiburg) asked us to provide them with 4 semi-autonomous robotic platforms.

These robots will be used in a project of assistance with household chores (recognition and manipulation of various items, placed at different heights).

GR LAB: Génération Robots’ engineering department

Génération Robots is a robotics integrator. We can manage your project from A to Z. We
draw up the specifications with you and deliver a full turnkey project.

We design robots that can fit a wide range of needs, we also develop softwares and algorithms necessary to the operation of autonomous or semi-autonomous robots.

We have built or heavily customize different autonomous robots, both indoor and outdoor.

Robot mobile Scoutsan by Génération Robots

Equipement selection

RIDGEBACK ROBOT by Clearpath Robotics

Ridgeback - Plateforme mobile omnidirectionnelle

TLT TELESCOPIC COLUMN by Exellix

Colonne téléscopique TLT Exellix

7 AXES ROBOT ARM by Franka Emika

Bras robotique 7 axes Franka Emika

UST-30LX LIDAR HOKUYO

LiDAR UST-30LX Hokuyo

Technical challenge #1: Design of a single button for 3 mobile elements

Why?

  • More convenient
  • Extra safety for the operator

To add extra safety and convenience, our team has set up the Ridgeback’s emergency stop button so that it stops the entire robotic solution (mobile platform, robotic arm, telescopic column,
computers).

Technical challenge #2: A telescopic column not designed for mobile robots

NO ROS COMPATIBILITY

The TLT Ewellix column did not have any ROS driver (Robot Operating System).

We developed a ROS package for the column (available on
our GitHub) and we created a digital twin of the column in
Gazebo thanks to the 3D models provided by the manufacturer.

Our engineers have also created a digital twin of the robot so that the customer can run simulations.

Jumeau numérique Cas client Freiburg

POWERING UP THE TELESCOPIC COLUMN

The Ewellix TLT column is powered with 24V, it is the output voltage of the Ridgeback mobile robot

In order to maintain a steady tension, our team added a converter (the output tension of the robot fluctuates depending on the battery charge level, it goes from 23V up to 28V).

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Technical challenge #3: An arm that requires an operating voltage of 230V

POWER COMPLEXITY

The Panda arm is controlled by a controller that works with 230V* = mains voltage

Our engineers have added a DC/AC voltage inverter to transform the 24V DC into 230V AC.

This solution makes it possible to power the arm with the battery of the mobile robot. It also offers the possibility of connecting a PC in tower format (voltage of 230 V required).

Indeed, the university needed to do object recognition with this
robot, it needed a powerful graphics card. These boards are only compatible with PC towers.

ISSUE IDENTIFIED

The battery of the mobile robot will discharge quite quickly
(1 hour of autonomy in active mode) because it is very solicited by the PC tower, the column and the arm.

POSSIBLE SOLUTION TO EXTEND THE BATTERY LIFE

Additional lead-acid batteries would be too heavy for the mobile robot (requirement: 2x 30 kg batteries ), which
already carries the column and the robot arm.

Lithium-ion or LiFePo4 batteries could be considered here. For the experiment planned by the customer, 1 hour battery life in operating mode is sufficient (1 day in
standby mode).

POTENTIAL UPGRADES

Our customer has the possibility to improve the
battery life of the robot. We have provided him with comprehensive wiring diagrams. The researchers who will be using the robotic platform have the
skills to develop such upgrades.

Axel Farenc, ingénieur en robotique chez Génération Robots

Technical challenge #4: Insufficient range of motion in the robot arm

IDENTIFIED PROBLEM

Robotic arms are usually mounted at the top of a telescopic column. This position restricts the arm’s range of motion, especially when picking up objects on the ground.

FROM CAD TO CNC

Design of a small metal platform, that will be fitted on the column, so the robot arm can be mounted at a lower level on the column.

The design and the setup of this positioning frame part had to be done in such a way that nothing would interfere with the deployment of the column.

The first part was machined in aluminum. This material turned out to be too soft and the structure sometimes entered in resonance. Machining a steel part solved this issue.

The shape of the part was also tweaked to better absorb forces and vibrations. In the end, our team managed to achieve a near-zero frequency vibration.

Modèle 3D de la plateforme en métal - Cas client Freiburg

Technical challenge #5: Teleoperation & Battery life

Intégration de 4 robots mobiles omnidirectionnels avec des bras collaboratifs sur colonne télescopique

TELEOPERABLE BUT SCABLE

Within the context of the project, the client requested a mobile robot that was ready to receive navigation algorithms and autonomous gripping algorithms.

As specified in the client’s brief, we delivered a teleoperable mobile robot, with everything setup to quickly achieve robotic autonomy. Our team added 2 Hokuyo UST30-LX LiDAR. Our, team also set up all the ROS drivers required for each component.

As part of its experimentation, the university’s researchers will be able to quickly upload their own programs.

Our team has made sure that the telescopic column can also be driven with the same joystick that controls the Ridgeback.

Conclusion

Our team delivered a comprehensive robotic solution, that
features:

  • 1x mobile robot
  • 1x telescopic column
  • 1x 7-axis arm
  • 2x LiDAR
  • 2x computers
  • 1x depth camera mounted on a pan-tilt

We have assembled, programmed and delivered in Germany 4 units of this robot. It took our team 3 months and a half to complete the project (from the brief to the handover).

As we have a subsidiary in Germany, we are able to provide a close follow-up to the customer.

Challenges successfully overcome
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