Robot External Force Limits for Precise Workpiece Positioning
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Solution Overview
Problem
Existing robot systems face challenges in efficiently managing external forces to prevent damage to constituent members while maintaining productivity, often leading to increased operation times and reduced productivity due to excessive force detection and automatic stops.
Innovation Solution
A calculation device and robot controller that determine an allowable value of external force based on the robot's position, orientation, and constituent member loads, allowing for controlled operation within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a force sensor is attached to the robot to detect external forces for precise workpiece positioning, then the positioning precision is improved, but the device complexity increases
Solution Approach 1:
The patent introduces a force sensor as an intermediary device attached between the robot hand and the workpiece. This sensor mediates the interaction by detecting external forces applied during workpiece positioning, enabling precise adjustment without requiring complex mechanical coupling or direct physical intervention. The force sensor translates physical contact forces into measurable signals that the control system can process for accurate positioning.
2Reliability
If the target value of external force is set low to prevent damage to robot constituents, then the reliability is improved, but the productivity deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of the target external force value based on the robot's current position, orientation, and the specific operation being performed. Instead of using a fixed conservative low force value, the system dynamically calculates and adjusts the appropriate force target within safe limits. This allows the robot to apply higher forces when structurally safe, thereby improving productivity while maintaining reliability through real-time monitoring and adjustment.
Solution Approach 2:
The system changes the parameter of target external force based on operating conditions such as robot position, orientation, and constituent member load capacity. By adjusting this parameter dynamically rather than maintaining a fixed low value, the system optimizes both reliability and productivity. The control unit modifies the force parameter in real-time to match the structural capacity and operational requirements.
3Reliability
If the robot controller performs automatic stop control when external force exceeds allowable value, then the reliability is improved, but the productivity deteriorates due to increased cycle time
Solution Approach 1:
The patent implements preliminary action by pre-calculating and setting appropriate target values for external force before operations begin. The system determines safe force targets based on robot configuration, workpiece properties, and constituent member capacity in advance. This preliminary setup prevents force exceedances before they occur, eliminating the need for automatic stops and recovery operations, thereby maintaining both reliability and productivity.
Solution Approach 2:
The system employs feedback control by continuously monitoring the actual external force through the force sensor and comparing it against the dynamically calculated target value. When the actual force approaches or exceeds the target, the control unit automatically adjusts the robot's position or orientation to reduce the force, preventing damage without requiring complete stops. This closed-loop feedback maintains reliability while minimizing interruptions to productivity.
Data Source
AI summary
This control device is provided with a processing unit for calculating a permissible value of an external force that is permissible to be applied on a robot, a workpiece, or a hand. The permissible value of load that can be exerted on a constituent member of the robot is determined in advance. The processing unit calculates a permissible value of an external force in an application direction in which the external force is applied, on the basis of the position and attitude of the robot, the position of an application point where the external force is applied, and the permissible value of load of the constituent member of the robot.