Robotic Force Torque Sensor Gravity Inertial Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Robotic force/torque sensors face inaccuracies in measuring forces and torques due to gravitational and inertial effects, which can exceed desired contact forces and torques, making force control operations difficult or impossible, especially during tasks involving changes in orientation and position.
Innovation Solution
The implementation of a compensation method that calculates and subtracts gravitational and inertial forces from measured force/torque data using a combination of inertial measurement units, forward kinematics, and parameter identification to isolate contact forces, involving the use of a rotation matrix, mass, angular velocity, angular acceleration, and inertia tensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gravitational and inertial effects are included in force/torque measurements, then the measurements reflect total forces experienced by the robot, but the accuracy of contact force measurements deteriorates because gravitational and inertial forces can exceed desired contact forces
Solution Approach 1:
The patent extracts and separates gravitational and inertial force components from the total force/torque measurements. By calculating these interference forces independently using robot kinematics and dynamics models, the system removes them from the measured signals to isolate the contact forces between the tool and workpiece, thereby improving measurement precision.
Solution Approach 2:
The patent introduces robot kinematics and dynamics models as intermediary computational systems. These models serve as mediators that process raw sensor data along with robot state information (position, velocity, acceleration) to compute and subtract gravitational and inertial effects, enabling accurate contact force measurement without direct physical separation.
2Measurement precision
If the robot maintains static orientation for thermal compensation, then thermal drift is compensated accurately, but the robot cannot perform dynamic tasks requiring orientation changes such as contour following and 3D parts assembly
Solution Approach 1:
The patent transitions from static thermal compensation to dynamic compensation by continuously updating the robot's orientation and position data during operation. The system adapts the compensation calculations in real-time based on changing robot configurations, enabling accurate force measurements even during dynamic tasks like contour following and 3D assembly operations.
Solution Approach 2:
The patent performs preliminary identification of gravitational and inertial parameters during robot operation. By continuously calculating and compensating for these effects based on real-time robot state, the system prepares and maintains accurate contact force measurements before they are needed for control, enabling both thermal compensation and task adaptability.
3Ease of operation
If force/torque sensors are used for force control operations, then the robot can apply controlled forces to workpieces, but the complexity of the control system increases due to the need for gravitational and inertial compensation calculations
Solution Approach 1:
The patent creates a universal compensation framework that handles both gravitational and inertial effects within a single integrated computational system. This multi-functional approach consolidates multiple compensation calculations into one unified process, reducing overall system complexity while maintaining comprehensive force control capability across various robot operations.
Data Source
AI summary
Force and torque measurements from a robotic F/T sensor are compensated for the effects of gravity, and optionally additionally for the effects of robot motion. The weight of an attached tool Wtool, and a vector {right arrow over (r)}CG from the F/T sensor body CF origin to a center of gravity of the tool are obtained, such as from user input or by parameter identification. During a robotic operation, a rotation matrix RInternational CFBody CF from the F/T sensor body CF to an inertial reference frame is obtained, such as from an internal inertial measurement unit (IMU), or from forward kinematics data from the robot. The force and torque measurements resolved by the F/T sensor from transducer outputs are compensated for gravity based on the Wtool and {right arrow over (r)}CG, and the instantaneous value of RInternational CFBody CF. For inertial compensation, the additional information is obtained, including: the mass m of the attached tool; the angular velocity {right arrow over (ω)} of the F/T sensor body CF; the angular acceleration {dot over (ω)} of the F/T sensor body CF; the linear acceleration {right arrow over (a)} of the F/T sensor body CF; and inertia tensor I defined in the F/T sensor body CF which contains all moments and products of inertia. The force and torque measurements resolved by the F/T sensor from transducer outputs are compensated for inertial effects based on m, {right arrow over (ω)}, {right arrow over (ω)}, {right arrow over (r)}CG, {right arrow over (α)}, and I.