Multi-Reference Impedance Control for Multi-Pin Robot Assembly
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Solution Overview
Problem
Industrial robots face difficulties in performing complex assembly tasks, such as inserting multiple pins into multiple holes, due to challenges in detecting and correcting minor misalignments, and existing impedance controllers require intricate gain tuning that is application-specific and unintuitive.
Innovation Solution
An impedance controller using multiple reference centers with only translational spring-damping gains, where the same gain factors are applied across all centers, simplifying tuning and eliminating the need for rotational gains, calculates spring-damping forces based on reference center positions and velocities, and sums these with measured contact force and torque to determine a new component pose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional impedance controller with one reference center and two groups of gains (linear and angular) is used, then the robot can perform impedance control for assembly tasks, but the gain tuning becomes difficult and unintuitive, especially the relationship between angular gain and linear gain
Solution Approach 1:
The patent segments the impedance control into multiple independent reference centers, each with its own spring-damper model. This allows the complex angular gain tuning to be broken down into simpler translational gain adjustments at each reference center, making the system easier to tune while maintaining reliable impedance control performance
Solution Approach 2:
The patent changes the parameter representation from angular gains to translational gains at multiple reference centers. By using position and velocity parameters at each reference center with translational spring-damper coefficients, the system achieves the same control objective with more intuitive and easier-to-tune parameters
2Reliability
If a system model is tuned to one assembly application, then it achieves good performance for that specific application, but it cannot be applied to other applications with different part geometries or structural properties
Solution Approach 1:
The patent creates a universal impedance control framework using multiple reference centers that can be applied to different assembly applications. By defining reference centers at key geometric features and using translational gains, the same control structure adapts to various part geometries and structural properties without requiring complete retuning, achieving both reliability and versatility
3Device complexity
If a single reference center impedance controller is used, then the control structure is simple, but it cannot effectively handle complex misalignments in multi-pin insertion tasks
Solution Approach 1:
The patent segments the single reference center into multiple reference centers distributed at key locations on the component. This segmentation allows the controller to detect and correct misalignments at multiple points simultaneously, improving alignment accuracy for multi-pin insertion while keeping each individual reference center's control structure simple
Solution Approach 2:
The patent extends the control from a single-point (0D) or single-axis (1D) reference center to multiple points in 3D space. By distributing reference centers throughout the component geometry, the system gains dimensional coverage that enables detection and correction of complex spatial misalignments while maintaining computational simplicity
Data Source
AI summary
A method for controlling a robot to perform a complex assembly task such as insertion of a component with multiple pins or pegs into a structure with multiple holes. The method uses an impedance controller including multiple reference centers with one set of gain factors. Only translational gain factors are used—one for a spring force and one for a damping force—and no rotational gains. The method computes spring-damping forces from reference center positions and velocities using the gain values, and measures contact force and torque with a sensor coupled between the robot arm and the component being manipulated. The computed spring-damping forces are then summed with the measured contact force and torque, to provide a resultant force and torque at the center of gravity of the component. A new component pose is then computed based on the resultant force and torque using impedance controller calculations.