Robot Safety Control for Dynamic Stopping Time and Distance
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Solution Overview
Problem
Current methods for evaluating and ensuring an industrial robot's stopping time and distance are tedious, time-consuming, and lack flexibility due to the high degree of complexity in industrial manipulators with multiple degrees of freedom, often requiring conservative estimates and inaccurate kinetic energy calculations.
Innovation Solution
A robot system comprising a robotic manipulator with multiple degrees of freedom, a controller, and a safety system that allows users to configure stopping time and distance limits, dynamically calculating the maximum brake torque and force, and continuously monitoring motions to ensure safe stopping within defined limits, using a dynamic model to adjust trajectories and apply necessary braking forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If tables for given speeds, payloads, extensions and joint motions are used to evaluate stopping time, then the evaluation process becomes tedious and time consuming, but the high degree of flexibility in industrial manipulators makes it infeasible to provide comprehensive tables for all possible motions and payloads
Solution Approach 1:
The patent replaces the mechanical approach of using static tables with a computational approach. A safety system with a processor continuously calculates stopping time and distance using dynamic models, replacing the need for manual table lookup and interpolation. This computational substitution resolves the contradiction by making the evaluation process automated and adaptable to any robot configuration without requiring comprehensive pre-computed tables.
Solution Approach 2:
The patent implements dynamic calculation of stopping parameters based on real-time robot state. Instead of using static tables for fixed configurations, the system continuously updates stopping time and distance calculations based on current speed, payload, joint positions, and acceleration profiles. This dynamic approach allows the system to adapt to any configuration without requiring pre-computed tables for all possible states.
2Reliability
If interpolation between various tables is performed to evaluate stopping time, then the process becomes more complex, but the results are often overly conservative in the estimates
Solution Approach 1:
The patent replaces the interpolation method with direct computational calculation. Instead of estimating stopping time by interpolating between table values, the safety system processor directly calculates the stopping parameters using the robot's dynamic model, current state, and brake characteristics. This eliminates the need for interpolation entirely, providing accurate results without the complexity and conservativeness of table-based methods.
Solution Approach 2:
The system performs self-evaluation of stopping parameters using its own dynamic model and sensor data. The safety system continuously monitors robot state and autonomously calculates stopping time and distance without requiring external tables or manual intervention. This self-service approach provides accurate, real-time estimates adapted to the actual robot configuration and load conditions.
3Measurement precision
If absolute position sensors are used to obtain speed of the hazardous object, then the resolution of sensors is low resulting in an inaccurate instant speed calculation, but kinetic energy calculation requires accurate speed data
Solution Approach 1:
The patent replaces direct speed measurement from position sensors with computational speed derivation. The safety system processor calculates instantaneous speed by differentiating the position signal over time intervals, and calculates kinetic energy using this derived speed and the robot's mass properties from its dynamic model. This computational approach overcomes the low resolution limitation of absolute position sensors by using numerical differentiation and dynamic modeling to achieve accurate speed and kinetic energy calculations.
Data Source
AI summary
A robot system and method for conditionally stopping a robot, wherein a maximum stopping time and/or distance are defined by a user or integrator through a user interface as safety limits based on the risk assessment. The method provides the continuous calculation of the time and/or distance, which the robot would need to stop under maximum motor torque and/or brake appliance. The robot is stopped or the speed of the robot is reduced, if the calculated time and/or distance exceeds the maximum limit values set by the user or integrator. The method may also be used to program or generate the trajectories of the robot as not to exceed the speed of the movement under the condition of keeping the set maximum stopping time and/or distance as defined by a use.