In the field of Human-Robot Interaction (HRI), achieving flexibility in human-accompanying within real-world environments holds great potential for various applications but also poses significant challenges. Traditional methods typically restrict robots to fixed positions relative to humans, such as tracking from behind, in front, or side-by-side, which limits robot adaptability in dynamic workspaces. This study introduces a novel human-companioning strategy that uses Reinforcement Learning (DRL) to enable mobile robots to dynamically adjust their tracking positions according to varying conditions. An interaction space is defined to capture the relationship between the human and the robot while considering the environment, which serves as the basis for state spaces in DRL to assist the robot in adapting to environmental changes. A human-robot companion controller is developed by integrating Model Predictive Path Integral (MPPI) control with Control Barrier Functions (CBF), ensuring that the robot accurately follows the target's movement in both position and orientation while avoiding obstacles and enhancing social acceptance and safety. The proposed approach is evaluated in real-world scenarios, both indoors and outdoors, and compared with other studies. The results show that the proposed method improves the success rate and tracking accuracy by at least 24% and 47%, respectively, while enhancing human comfort. Experiments demonstrate the robot's ability to flexibly accompany a person walking at speeds of up to 1.7 m/s, dynamically adjusting its strategy without being confined to a fixed position. Additionally, the robot respects the human's intimate space to ensure safety, comfort, and effective obstacle avoidance.
Fig. 2 : Schematic model and generalized coordinates.
Fig. 3 : The overall structure of the system architecture. The robot observes the proposed cost functions, total cost, collision-free space, robot velocity, human position and velocity, obstacles, and previous actions. Policy determines an action index within the collision-free space and then provides a target position for the human-companion controller.
Fig. 4 : Illustration of the training environment.
Fig. 5 : Policy performance under varying hyperparameter configurations: (a) Proposed architecture and (b) RL baseline.
Fig. 6 : Simulation environment used for comparison.
Metrics
SR (%)
UT (s)
ex (m)
ey (m)
eθ (rad)
PID [ 2 ]
0
-
-
-
-
DWA [ 5 ]
34
33.0±8.5
0.97±0.25
0.88±0.22
0.71±0.18
MPC [ 31 ]
46
21.0±5.4
0.41±0.13
0.43±0.14
0.23±0.06
DRL [ 29 ]
62
27.0±6.3
0.17±0.07
0.21±0.11
0.20±0.08
Proposed
86
2.5±0.8
0.09±0.03
0.05±0.02
0.08±0.03
TABLE II : Quantitative Results of Comparison.
Fig. 7 : Distribution of robot positions relative to the human across four experimental scenarios.
Fig. 8 : Tracking performance and user scores under different interaction-space configurations.
Fig. 9 : Tracking performance of the proposed controller in indoor scenarios: relative positions of the following point to the human ( xdh , ydh ) and the robot ( xdr , ydr ), tracking errors ( ex , ey , eθ ), and the distance between the human and the robot ( dhr ).
Fig. 10 : Trajectories of the human and robot in four indoor scenarios.
Fig. 11 : Human and robot trajectories in indoor occlusion scenarios (doorway and multi-pedestrian).
Method
Success Rate (%)
Frequency (Hz)
Lighting Robustness
FoV
Camera
55
≈30
Low
110∘
LiDAR
39
≈9
High
360∘
AmfiTrack
92
≈120
High
Omni
TABLE III : Quantitative Performance Comparison of Tracking Hardware Systems.
Fig. 12 : Tracking accuracy at different walking speeds.
Fig. 13 : Tracking performance under various obstacle conditions.
Fig. 14 : Outdoor experimental environments.
Fig. 15 : Tracking performance on asphalt and brick roads.
Pedestrians
SR (%)
UT (s)
APT (ms)
5
81
1.35
9.86
10
65
2.79
10.01
15
33
7.13
10.93
20
26
9.22
11.85
TABLE IV : Quantitative Performance across Crowd Densities.
Department of Engineering "Enzo Ferrari", University of Modena and Reggio Emilia, Italy. · Department of Surgery, Medicine, Dentistry and Morphological Sciences, University of Modena and Reggio Emilia, Italy.