Conservative Force Field for Robot Dynamics Compensation
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Solution Overview
Problem
Robot devices, particularly those used in rehabilitation, face challenges in minimizing the influence of their own dynamics during dynamic movements, leading to increased interaction forces and torques with operators, which can limit versatility and effectiveness.
Innovation Solution
A method involving a conservative force field module that calculates compensation forces based on a dynamic model of the robot, using predefined trajectories to minimize interaction torques between the robot and operator, allowing for optimal compensation of robot dynamics while ensuring the force field is conservative, with no net energy exchange in closed trajectories.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the robot device is made lightweight to reduce inertial forces, then the inertial forces are reduced significantly, but the device cannot exert high forces and is less versatile
Solution Approach 1:
The patent applies counterweight principles by calculating compensation forces that act opposite to the robot's own dynamic forces (inertia, gravity, Coriolis, centrifugal forces). The conservative force field generates compensating forces that counterbalance the robot's dynamics, effectively canceling out inertial effects without requiring the robot to be lightweight. This allows the robot to maintain its structural strength and versatility while experiencing reduced interaction forces during operation.
2Force
If gravity compensation is used to cancel gravitational forces, then gravitational forces are compensated, but inertial forces during dynamic motion are not addressed
Solution Approach 1:
The patent transitions from static gravity compensation to dynamic compensation by incorporating velocity and acceleration terms into the force field calculation. The conservative force field module computes compensation forces based on the robot's current position, velocity, and acceleration, as well as the desired trajectory. This dynamic approach addresses all dynamic motion effects including inertia, Coriolis, and centrifugal forces, not just gravitational forces, making the robot effective across the full range of motion speeds.
3Force
If force feedback via force sensors is used to reduce friction and inertia, then friction and inertia can be reduced, but inertial forces remain and force sensors are expensive
Solution Approach 1:
The patent replaces the mechanical force sensing approach with a computational model-based approach. Instead of using force sensors to measure and compensate for dynamic forces, the system uses a dynamic model to calculate the required compensation forces based on measured position, velocity, and acceleration. This substitution eliminates the need for expensive force sensors while achieving the same goal of reducing interaction forces through accurate dynamic compensation.
4Force
If Series Elastic Actuators are used to reduce inertial forces from drives, then inertial forces from drives are reduced, but inertial forces from end-effector remain and maximum stiffness must be compromised
Solution Approach 1:
The patent introduces a conservative force field module as an intermediary computational layer between the controller and the actuator. This module calculates compensation forces that account for all sources of robot dynamics including the end-effector's inertia, which Series Elastic Actuators alone cannot address. The force field acts as a virtual intermediary that generates the precise compensation forces needed, allowing the physical actuators to maintain their optimal stiffness characteristics while the computational layer handles the dynamic compensation.
Data Source
AI summary
A method to control a robot device that includes at least one manipulator which is moveable in an operating space, at least one actuator which actuates the manipulator, a sensor arrangement having at least one position sensor to determine the actual position of the manipulator and a controller which controls the actuator. The manipulator moves along an actual trajectory by means of an external force provided by an operator. The actuator provides compensation forces onto the manipulator influencing the torques or forces exchanged between operator and manipulator. The controller includes a conservative force field module having a conservative force field. The controller provides control signals for the actuator which provides the compensation force based on the control signals. The control signals are based on the conservative force field and on the actual position of the manipulator.