Pneumatic Force Control Transfer to Prevent Contact Force Overshoot
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Solution Overview
Problem
Robotic material removal tools experience force overshoot during initial contact with a workpiece, leading to poor finish quality or damage, due to challenges in real-time force adjustments and compliance issues.
Innovation Solution
A force control device with a pneumatic cylinder that transitions from position control to force control mode upon contact detection, using a bumpless transfer method to ramp the applied force to a setpoint, adjusting pneumatic pressures for compliance and stiffness, and employing steady or transient search methods to detect contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a robotic material removal tool is used with a pneumatic force control device, then compliance and force control are improved, but impact force overshoot occurs upon initial contact with the workpiece
Solution Approach 1:
The system performs preliminary positioning of the robotic tool near the workpiece surface using position control mode before initiating force control. This preliminary action allows the system to establish a safe starting position and detect contact before full force is applied, preventing impact overshoot while maintaining compliance benefits
Solution Approach 2:
The system dynamically switches between position control mode and force control mode based on contact detection status. Before contact, position control provides stable positioning; after contact detection, force control activates to regulate contact force. This dynamic mode transition resolves the contradiction by adapting the control strategy to the operational phase
2Measurement precision
If real-time force adjustments are made during material removal, then force control precision is improved, but the stiffness of the robot arm and positioning granularity make real-time adjustments difficult or impossible
Solution Approach 1:
The control system is segmented into two distinct modes: position control mode for approach and positioning, and force control mode for contact force regulation. This segmentation allows each mode to be optimized independently - position control leverages the robot's positioning accuracy while force control provides precise force regulation, avoiding the complexity of attempting real-time force adjustments in a single unified control system
3Measurement precision
If the robotic tool is positioned precisely along a compliance stroke, then positioning accuracy is improved, but contact detection and force transition become more complex
Solution Approach 1:
The system uses feedback from force sensors to detect contact between the robotic tool and workpiece. When contact force exceeds a threshold, the system transitions from position control to force control mode. This feedback mechanism simplifies contact detection by using readily available force sensor data rather than requiring complex position-based contact detection algorithms
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Mitigates impact force overshoot, ensuring consistent and safe contact forces, preventing damage and improving workpiece finish quality.
Implementation Method 1
adjusting pneumatic pressures for compliance and stiffness
Data Source
AI summary
A force control device mitigates or eliminates impact force overshoot upon contact between a robotic tool and a workpiece. Contact is detected while operating the force control device in a position control mode, according to either of a steady state search method or a transient search method. The force applied to the workpiece upon contact is less than a predetermined setpoint force. Upon detecting contact, the force control device performs a bumpless transfer to a force control mode. In force control mode, the force control device ramps the contact force to the predetermined setpoint. The force ramp may be linear, or along a user-defined trajectory. The stiffness of the force control device is different in position and force control modes, controlled by backpressure in a pneumatic cylinder.