Robotic Gripper Friction Estimation and Compensation
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Solution Overview
Problem
Pneumatic grippers face challenges in accurately controlling gripping force due to friction forces, which affect precision and reliability, especially as the distance from the gripper base increases, leading to difficulties in detecting contact, assessing grip quality, and controlling force application.
Innovation Solution
A gripper equipped with a jaw position sensor, gripping force sensor, and a processing unit featuring a friction estimation module and compensation module, which estimates and compensates for static and dynamic friction forces, allowing for precise control of the actuation group and improved positioning of the jaws.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If friction forces are present in the transmission group, then the gripper can operate with simple mechanical components, but the gripping force decreases rapidly with distance from the base and control precision deteriorates
Solution Approach 1:
The patent implements a feedback control system where sensors measure the actual gripping force and position, and the controller adjusts the actuation force accordingly. This closed-loop feedback compensates for friction effects and maintains precise control despite the presence of friction in the transmission group.
Solution Approach 2:
The patent dynamically adjusts control parameters including actuation force, velocity, and acceleration based on real-time measurements. By changing these parameters adaptively, the system compensates for friction variations and maintains precise gripping force control across different operating conditions.
2Device complexity
If friction forces act on the jaws, then the gripper structure remains simple, but detection of contact and assessment of grip quality become difficult
Solution Approach 1:
The patent uses sensors to continuously monitor gripping force and position, providing feedback that enables detection of contact between jaws and item. The controller processes this feedback information to assess grip quality and distinguish between different contact states despite friction presence.
Solution Approach 2:
The patent introduces sensors as intermediary elements between the mechanical gripper components and the control system. These sensors mediate the detection process by converting mechanical quantities (force, position) into electrical signals that can be processed for contact detection and grip quality assessment.
3Ease of operation
If proportional-integral control or sliding mode control is used, then force control is improved, but friction compensation remains insufficient and measurement precision is limited
Solution Approach 1:
The patent extends beyond traditional PID or sliding mode control by dynamically adjusting multiple parameters including velocity and acceleration profiles. This multi-parameter adaptive control provides better friction compensation and measurement precision compared to conventional single-parameter control approaches.
Solution Approach 2:
The patent implements enhanced feedback control that specifically addresses friction compensation. The controller uses real-time feedback from force and position sensors to calculate and compensate for friction effects, providing more accurate measurement precision than conventional control methods.
4Device complexity
If pneumatic actuation is used, then the gripper can be compact and simple, but precise positioning of jaws at intermediate positions cannot be achieved
Solution Approach 1:
The patent uses position sensors to provide feedback on jaw position, enabling the controller to achieve precise positioning at intermediate positions. The feedback control compensates for pneumatic system compressibility and friction effects, maintaining positioning precision throughout the full range of motion.
Solution Approach 2:
The patent dynamically controls the pneumatic actuation system by adjusting pressure, velocity, and acceleration parameters in real-time. This dynamic control enables precise positioning at intermediate positions by adapting the actuation characteristics to the specific positioning requirements.
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 enables accurate detection of contact, precise control of gripping force, and improved handling of items by compensating for friction forces, enhancing the gripper's precision and reliability in robotic applications.
Implementation Method 1
estimating the static and/or dynamic friction forces acting upon the components of the transmission group and upon the jaws, the static friction forces being calculated by the estimation module on the basis of the constraining reactions to which the components of the transmission group and the jaws are subjected
Implementation Method 2
a jaw position sensor that is suitable for measuring the absolute position of the jaws
Implementation Method 3
a possible gripping force sensor that is suitable for measuring the gripping force exerted by the jaws upon the item
Implementation Method 4
The actuation group is operatively coupled to the at least one movable jaw by means of the transmission group in order to move the movable jaw between the opening position and the closing position
Data Source
AI summary
A gripper which has a friction estimation module configured to estimate static and/or dynamic friction forces acting on gripping jaws is provided. The static friction force is calculated on the basis of constraining reactions whereto the gripping jaws are subjected, the constraining reactions being calculated at least as a function of an actuation force exerted on the gripping jaws, a coefficient of friction of gripper materials and/or lubricant used being known. The dynamic friction force is calculated on the basis of speed of the gripping jaws, width of sliding surfaces and distance between the sliding surfaces of the gripping jaws, the viscosity of the lubricant used being known.