Force-Controlled Tool Handling for Precise Surface Machining
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Solution Overview
Problem
Conventional industrial robots are inadequate for precise force control during surface machining processes due to their high inertia, which makes it difficult to maintain the process force within a desired range, potentially damaging workpieces and incurring high repair costs.
Innovation Solution
A force-controlled handling apparatus with a linear actuator and a force sensor is used between the manipulator and the machine tool, allowing for precise control of the contact force between the tool and the workpiece, while the manipulator moves along a predefined trajectory, using a state observer to estimate and adjust the force based on target values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional industrial robot is used for surface machining, then the manipulator can move the tool along a desired trajectory with position control, but the large inertia of the robot arm segments prevents the controller from reacting quickly enough to variations in process force, making precise force control difficult to achieve
Solution Approach 1:
The system is segmented into two independent control functions: the manipulator handles position control (moving the tool along the trajectory) while the separate linear actuator handles force control (maintaining contact force). This segmentation allows each component to be optimized for its specific function, enabling precise force control without being constrained by the manipulator's inertia.
Solution Approach 2:
A linear actuator is introduced as an intermediary device between the manipulator and the tool. This intermediary component specifically handles force control, allowing the manipulator to focus on position control while the linear actuator responds quickly to force variations, thereby resolving the contradiction between position accuracy and force control speed.
2Reliability
If the process force becomes too high during machining, then the workpiece may be damaged or destroyed, but maintaining precise force control within the desired range requires sophisticated control systems that conventional robots lack
Solution Approach 1:
By separating force control from position control into distinct components (linear actuator for force, manipulator for position), the system achieves reliable workpiece protection through a dedicated force control mechanism without requiring the entire robot system to be overly complex.
Solution Approach 2:
The control system continuously monitors the contact force between tool and workpiece and adjusts the linear actuator's output force accordingly to maintain the process force within the desired range. This feedback mechanism ensures workpiece protection while keeping the control system manageable in complexity.
3Force
If a small lightweight handling apparatus is used between the manipulator and tool to improve force control, then force control precision is improved, but the system becomes more complex with additional components
Solution Approach 1:
The linear actuator serves as a focused intermediary component that provides the necessary force control precision. By concentrating the force control function in this single dedicated component rather than attempting to achieve it through the entire robot system, the added complexity is minimized while still achieving the desired precision.
Solution Approach 2:
The handling apparatus integrates multiple functions: it couples the manipulator to the tool, enables force control through the linear actuator, and maintains the tool along the desired trajectory. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in overall system complexity.
Data Source
AI summary
An embodiment relates to a handling apparatus with a linear actuator acting between a first flange connectable to a manipulator and a second flange to which a tool, or a machine tool with a tool, can be mounted. The linear actuator exerts a force on the second flange, or an end stop, in accordance with a control variable. The device further comprises a force sensor coupled between the second flange and the tool and configured to measure a force exerted by the handling apparatus on the tool upon contact between the tool and a surface. A control unit comprises a state observer configured to determine an estimated value for the force exerted by the handling apparatus on the tool based on the control variable. The control unit is further adapted to detect a contact between the tool and the surface, wherein the control variable is adjusted based on the estimated value and a target value as long as no contact is detected, whereas the control variable is adjusted based on the measured force and the target value as long as a contact is detected.