Organizations: State Key Laboratory of Mechanical System and Vibration, Institute of Robotics, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China
Collaborative robots are increasingly deployed in industrial scenarios characterized by frequent product changeovers. As an intuitive programming method, kinesthetic teaching facilitates rapid robot deployment. However, users may overlook the configuration of the robot during kinesthetic teaching, leading to degradation in operational performance. Operational performance refers to the capability of the robot to generate motion and can be quantified by the Minimum Singular Value of the Jacobian matrix. To address this issue, this paper proposes an online dynamic force guidance method that integrates performance constraint and optimization mechanisms. Specifically, variable admittance control maintains the operational performance of the robot above a predefined threshold, while a virtual force actively guides the user to drag the robot towards configurations with improved performance. Experiments are conducted on a 6-DOF collaborative robot, comparing three typical paths in the task space. To evaluate the quality of the taught trajectories, trajectory playback experiments are conducted to analyze the relationship between the operational performance of the robot and the work efficiency. The results demonstrate that the proposed method effectively enhances the operational performance of the robot and consequently improves the work efficiency, holding significant value for reducing production takt time in industrial deployment.
Figures & tables
Figure 1: Paths crossing and bypassing the singularity. The red dashed line indicates the shoulder singularity, which is a cylindrical surface centered at the base coordinate origin.
Figure 2: Block diagram of the control structure. The performance constraint module dynamically adjusts the controller parameters based on the robot state. The performance optimization module generates a virtual force, which is combined with the operational force and sent to the adjusted admittance controller. The controller outputs the desired end-effector velocity, which is converted to joint velocity via the inverse Jacobian matrix and sent to the robot.
Figure 3: Influence of control parameters on dynamic force. (a) Admittance parameters. (b) Virtual force. The control parameters can be reasonably selected according to task requirements to adjust the magnitude and effective range of the dynamic force.
Figure 4: The mechanism of the dynamic force guidance. (a) Kinesthetic teaching with dynamic force guidance. (b) Control principle.
Figure 5: Experimental platform.
Performance constraint
Performance optimization
Parameter
Value
Parameter
Value
ζH
100
fmax(N)
15
ζL
15
k
24
σ0
96
lH
1
lL
0.5
Admittance parameters
Table 1: Control parameters used in the experiment
Figure 6: Experimental setup and performance indices. (a) Guide rails for three typical paths. (b) Taught trajectories and corresponding performance indices.
Figure 7: Real-world kinesthetic teaching demonstrations. (a) DT strategy on Path 2. (b) DFGT strategy on Path 2. (c) DT strategy on Path 3. (d) DFGT strategy on Path 3. The situation for Path 1 is similar to that of Path 2. The DT strategy reaches the singularity under both Path 1 and Path 3, leading to the termination of the kinesthetic teaching process.
Figure 8: Joint velocity and virtual force under different control strategies. (a) Direct Teaching. (b) Variable Admittance Teaching. (c) Dynamic Force Guided Teaching. Each row corresponds to one predefined path.
Figure 9: Statistical results of evaluation metrics for different control strategies on Path 2. (a) Trajectory length. (b) Minimum Singular Value. (c) Actual execution time. Asterisks indicate statistical significance: ∗∗p<0.001 .
Strategy
Length (mm)
MSV
Tex (s)
Fhmax (N)
DT
420.22
23.92
7.66
4.76
VAT
435.80
70.83
7.00
8.83
DFGT
444.62
77.15
6.87
6.96
Table 2: Evaluation Metrics under Different Control Strategies on Path 2
Figure 10: End-effector velocity and MSV over time during the playback process. (a) Direct Teaching. (b) Dynamic Force Guided Teaching.