11
Oct, 2020

Hands-Free v2 to teleoperate robotic manipulators: three axis precise positioning study

HANDS-FREE V2

The idea of this thesis project is to improve the already developed teleoperation system presented at Ubiquitous Robotics by implementing the z-axis control. In fact, the original system only performed a xy teleoperation allowing users to move the end-effector of the robot to the desired position determined by the index finger keypoint extracted by OpenPose. However, a more interesting application also integrates a precise z-axis control and a trajectory planner, which are the key improvements of this version as seen in Fig. 1.

Fig. 1 - Concept of Hands-Free v2. By analyzing the hand skeleton using OpenPose it is possible to extract the index finger position over time to build a complete trajectory. The points are interpolated by the ad-hoc interpolator and the final trajectory is sent to the ROS node of the Sawyer robot.

SETTING UP THE SYSTEM

Due to the COVID-19 pandemic restrictions, this project has been carried out using ROS Gazebo to reproduce the laboratory set-up already seen for Hands-Free v1. The camera adopted is a consumer-end RGB camera that has been calibrated following the standard procedure described in Hands-Free v1 paper. The robot calibration has been similarly performed by setting up a simulated environment as shown in Fig. 2.

Fig. 2 - Example of the robot calibration procedure carried out into the simulated Gazebo environment.

BUILDING THE TRAJECTORY

The trajectory builder is an extension of the capabilities of the old version of the software, hence it only works in 2D considering the user frame (xy plane) and the vertical robot frame (zy plane). The procedure to use this application is the following and may be seen in the video below:

  1. Users place their hand open on the user frame in order to detect the “hand-open” gesture. This allows the system to reset the variables and move the robot to its home pose (Fig. 3)
  2. After the initialization phase, users may move their hand around the user frame performing the “index” gesture (with both thumb and index finger opened). The index finger position is extracted considering keypoint 8. Only positions which differ from the preceding one of at least 5 px are retained. Moreover, each position is extracted as the mean position detected over N consecutive frames. In this case, we set N = 3 (Fig. 4)
  3. The detected trajectory points are filtered and interpolated according to the ad-hoc interpolator developed. The resulting trajectory may be sent to the robot if the “move” gesture is performed (with index and middle fingers opened, see Fig. 5).
Fig. 3 - Example of the initialization phase performed by using the "hand-open" gesture.
Fig. 4 - Example of the definition of a trajectory by performing the "index" gesture. The trajectory points are saved and filtered according to their position with respect to the preceding point.
Fig. 5 - Example of the launch of the interpolated trajectory, performed by using the "move" gesture.

Z-AXIS CONTROL

To control the manipulator along the z-axis (which in this set-up corresponds to the robot’s x-axis) three different modalities have been studied and implemented. For now, however, the depth control is still separate from the trajectory planner.

KEYBOARD

Intuitively, by using this mode the robot may be moved home (h), forward (w), or backward (s) according to the pressed key of the keyboard. The stepsize of its movement is fixed. By pressing ctrl+c or esc it is possible to exit the modality and close the communication with the robot.
 

FINGERS DISTANCE

In this modality, the core functions of Hands-Free are retained in order to detect the hand gestures. However, in this case, only the “hand-open” gesture and the “move” gesture are detected. By checking the mutual distance between the two fingers of the “move” gesture it is possible to detect if the robot should move forward (small distance up to zero) or backward (higher distance, corresponding to the original “move” gesture with the two fingers quite separate from each other). An example of this modality may be seen in the video below.
 

KAI SENSOR

The last modality implements depth control by leveraging the Vicara Kai wearable sensor. The sensor should be wear on the hand and, according to the detected orientation of the opened hand, it is possible to determine if the robot should stay still (hand parallel to the ground), move forward (hand tilted down), or backward (hand tilted up).

RELATED PUBLICATION

C. Nuzzi, S. Ghidini, R. Pagani, S. Pasinetti, G. Coffetti and G. Sansoni, “Hands-Free: a robot augmented reality teleoperation system,” 2020 17th International Conference on Ubiquitous Robots (UR), Kyoto, Japan, 2020, pp. 617-624, doi: 10.1109/UR49135.2020.9144841.

4
Jun, 2019

Real-Time robot command system based on hand gestures recognition

With the Industry 4.0 paradigm, the industrial world has faced a technological revolution. Manufacturing environments in particular are required to be smart and integrate automatic processes and robots in the production plant. To achieve this smart manufacturing it is necessary to re-think the production process in order to create a true collaboration between human operators and robots. Robotic cells usually have safety cages in order to protect the operators from any harm that a direct contact can produce, thus limiting the interaction between the two. Only collaborative robots can really collaborate in the same workspace as humans without risks, due to their proper design. They pose another problem, though: in order to not harm human safety, they must operate at low velocities and forces, hence their operations are slow and quite comparable to the ones a human operator does. In practice, collaborative robots hardly have a place in a real industrial environment with high production rates.

In this context, this thesis work presents an innovative command system to be used in a collaborative workstation, in order to work alongside robots in a more natural and straightforward way for humans, thus reducing the time to properly command the robot on the fly. Recent techniques of Computer Vision, Image Processing and Deep Learning are used to create the intelligence behind the system, which is in charge of properly recognize the gestures performed by the operator in real-time.

Step 1: Creation of the gesture recognition system

A number of suitable algorithms and models are available in the literature for this purpose. An Object Detector in particular has been chosen for the job, called “Faster Region Proposal Convolutional Neural Network“, or Faster R-CNN, developed in MATLAB.

Object Detectors are especially suited for the task of gesture recognition because they are capable to (i) find the objects in the image and (ii) classify them, thus recognizing which objects they are. Figure 1 shows this concept: the object “number three” is showed in the figure, which the algorithm has to find. 

Fig. 1 - The process undergone by Object Detectors in general. Two networks elaborate the image in different steps: first the region proposals are extracted, which are the positions of object of interest found. Then, the proposals are evaluated by the classification network, which at the end outputs both the position of the object (the bounding box) and the name of the object class.

After a careful selection of gestures, purposely acquired by means of different mobile phones, and a preliminary study to understand if the model was able to differentiate between left and right hand and at the same time between the palm and the back of the hand, the final gestures proposed and their meaning in the control system are showed in Fig. 2.

Fig. 2 - Definitive gesture commands used in the command system.

Step 2: creation of the command system

The proposed command system is structured as in Fig. 3: the images are acquired in real-time by a Kinect v2 camera connected to the master PC and elaborated in MATLAB in order to obtain the gesture commands frame by frame. The commands are then sent to the ROS node in charge of translating the numerical command into an operation for the robot. It is the ROS node, by means of a purposely developed driver for the robot used, that sends the movement positions to the robot controller. Finally, the robot receives the ROS packets of the desired trajectory and executes the movements. Fig. 4 shows how the data are sent to the robot.

Fig. 3 - Overview of the complete system, composed of the acquisition system, the elaboration system and the actuator system.
Fig. 4 - The data are sent to the "PUB_Joint" ROS topic, elaborated by the Robox Driver which uses ROS Industrial and finally sent to the controller to move the robot.

Four modalities have been developed for the interface, by means of a State Machine developed in MATLAB:

  1. Points definition state
  2. Collaborative operation state
  3. Loop operation state
  4. Jog state
Below you can see the initialization of the system, in order to address correctly the light conditions of the working area and the areas where the hands will probably be found, according to barycenter calibration performed by the initialization procedure. 
 
If you are interested in the project, download the presentation by clicking the button below. The thesis document is also available on request.
DOWNLOAD THE PRESENTATION

Related Publications

Nuzzi, C.; Pasinetti, S.; Lancini, M.; Docchio, M.; Sansoni, G. “Deep Learning based Machine Vision: first steps towards a hand gesture recognition set up for Collaborative Robots“, Workshop on Metrology for Industry 4.0 and IoT, pp. 28-33. 2018

Nuzzi, C.; Pasinetti, S.; Lancini, M.; Docchio, M.; Sansoni, G. “Deep learning-based hand gesture recognition for collaborative robots“, IEEE Instrumentation & Measurement Magazine 22 (2), pp. 44-51. 2019