TieBot: Learning to Knot a Tie from Visual Demonstration through a Real-to-Sim-to-Real Approach

Abstract

The tie-knotting task is highly challenging due to the tie's high deformation and long-horizon manipulation actions. This work presents TieBot, a Real-to-Sim-to-Real learning from visual demonstration system for the robots to learn to knot a tie. We introduce the Hierarchical Feature Matching approach to estimate a sequence of tie's meshes from the demonstration video. With these estimated meshes used as subgoals, we first learn a teacher policy using privileged information. Then, we learn a student policy with point cloud observation by imitating teacher policy. Lastly, our pipeline learns a residual policy when the learned policy is applied to real-world execution, mitigating the Sim2Real gap. We demonstrate the effectiveness of TieBot in simulation and the real world. In the real-world experiment, a dual-arm robot successfully knots a tie, achieving 50% success rate among 10 trials.

Video Summary

Pipeline Overview

Our pipeline first apply local feature matching and keypoints detection to estimate the mesh of the tie in the human demonstration, with a given mesh model. Then, we learn to select grasping points for robots using RL, and train a student policy to imitate the teacher policy. Finally, we learn a residual policy when deploying to real robots.

Human Demonstration

Human demonstration of the first tie-knotting task.

Human demonstration of the second tie-knotting task.

Human demonstration of the towel-folding task.

Local Feature Matching

We use LoFTr to build feature matching between two consecutive images. Here are some examples of feature matching results.

First tie-knotting task

Second tie-knotting task

Towel-folding task

Keypoints Detection

In our Real2Sim pipeline, we use existing estimated results to train keypoints detection model. Here we illustrate several detection results. The blue arrow is the predicted z-axis. The green arrow is the predicted x-axis.

First tie-knotting task

Second tie-knotting task

Real2Sim Results

Here we show several estimated meshes using our Real2Sim pipeline. The first and third columns are point clouds extracted from human demonstration video, and the second and forth columns are estimated meshes.

First tie-knotting task

Second tie-knotting task

Towel-folding task

Real-World Experiment

We test our real-world policy 10 times. Each time the initial positions of the tie are slightly perturbed about 5cm. The final success rate is 50%.