Robot Manipulator Impedance Control for Safe Human Contact
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Solution Overview
Problem
Existing robot manipulator control systems do not adequately ensure safe behavior during contact events with humans, as they lack effective mechanisms to regulate contact pressure and prevent tissue depression beyond safe limits.
Innovation Solution
A method and control unit for a robot manipulator that utilize a database of body zones with assigned maximum permissible contact pressures, impedance-regulated control, and sensors to detect and predict contact events, ensuring that contact pressure is maintained within safe limits and tissue depression is minimized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If robot manipulator operates with high force and speed for productivity, then productivity is improved, but contact pressure on human body may exceed safe limits causing injury
Solution Approach 1:
The control system dynamically adjusts the impedance parameters (stiffness and damping) of the robot manipulator in real-time based on the detected contact situation. When contact with a human is detected, the system transitions from a rigid high-force mode to a compliant low-impedance mode, allowing the manipulator to yield and reduce contact pressure automatically while maintaining operational effectiveness
Solution Approach 2:
The system employs force sensors to continuously monitor contact forces between the manipulator and the human body. This feedback information is fed back to the control unit, which compares the measured contact pressure against pre-stored safety thresholds for different body zones. When unsafe contact pressure is detected, the control system immediately adjusts the manipulator's impedance to reduce the force, creating a closed-loop safety control mechanism
2Manufacturing precision
If robot manipulator uses rigid control for precision positioning, then positioning precision is improved, but tissue depression and injury risk increase during contact
Solution Approach 1:
The system implements dynamic impedance control that adjusts the manipulator's mechanical compliance based on operational context. During normal operation, the manipulator maintains rigid control for precision positioning. Upon detecting contact with a human body, the system dynamically switches to a compliant mode with reduced stiffness, allowing the manipulator to yield to tissue deformation and minimize depression depth while maintaining control
Solution Approach 2:
The control system changes the impedance parameters (particularly stiffness and damping coefficients) of the manipulator based on the detected contact situation. By adjusting these parameters from high values during normal operation to low values during human contact, the system achieves both precision positioning capability and tissue protection, as the softened manipulator conforms to body contours without excessive force
3Reliability
If robot manipulator implements soft and compliant behavior for safety, then safety is improved, but operational force and productivity decrease
Solution Approach 1:
The manipulator employs dynamic impedance control that switches between rigid and compliant behaviors based on operational context. During normal non-contact operation, the manipulator maintains high stiffness and force capability for productive work. Upon detecting contact with a human body through force sensors, the system dynamically transitions to a compliant low-impedance mode, ensuring safety while preserving full operational capability when needed
Solution Approach 2:
The system pre-stores safety threshold values for contact pressure in different body zones and uses these to guide real-time control decisions. By having safety criteria prepared in advance and continuously monitoring against them, the system can immediately counteract potentially harmful contact forces while maintaining normal aggressive operation when safety thresholds are not violated, thus preserving productivity
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
The solution effectively reduces the risk of injury by ensuring that contact pressure is kept within safe limits and that tissue depression is minimized, providing a resilient and damped movement of the robot manipulator during contact with humans.
Implementation Method 1
controlling the robot manipulator in an impedance-regulated manner, such that the reference position serves as a zero position of an artificial spring component of impedance regulation
Data Source
AI summary
A method of controlling a robot manipulator, the method including: providing a database containing body zones of a person, wherein each of the body zones is assigned a respective maximum permissible value of contact pressure value, determining a current or a future contact event of the robot manipulator involving the person, and determining a body zone of the person that is contacted, determining a reference position fixed relative to a body of the person, wherein the reference position indicates beginning of a spatial progression of depression of tissue of the person during the contact event with the person, and controlling the robot manipulator in an impedance-regulated manner, such that the reference position serves as a zero position of an artificial spring component of impedance regulation of the robot manipulator and a maximum permissible contact pressure is not exceeded as a limit value.