Robot End-Effector Contact Force Control for Jerk-Free Surface Touch
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Solution Overview
Problem
Existing robot-supported automated systems face challenges in precisely recognizing contact moments and controlling contact forces, leading to shock-like forces that are undesirable in applications requiring precision, especially when handling sensitive workpieces.
Innovation Solution
A handling apparatus with a mechanical interface, gearless actuators, and a closed-loop control unit that adjusts force from a minimum to a desired level upon contact, using static friction-free actuators and a restoring spring to minimize jerking and maintain precise control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a robot-supported automated system contacts a surface, then the contact force can be regulated, but a shock-like contact force occurs which is undesirable in precision applications
Solution Approach 1:
The system performs preliminary actions by detecting contact moments in advance through sensor units and preparing the force regulation mechanism before actual contact occurs. The control unit anticipates contact events and pre-configures the actuator response, allowing the system to transition smoothly into contact without shock-like forces.
Solution Approach 2:
The patent implements beforehand cushioning by using compliant elements or controlled deceleration mechanisms that absorb impact energy before contact occurs. The system reduces the robot's approach speed or engages damping elements prior to contact, preventing the generation of shock-like contact forces while maintaining the ability to regulate contact force afterward.
2Speed
If a rigid system contacts a surface quickly, then positioning speed is improved, but even the smallest displacements result in a high increase in force
Solution Approach 1:
The system transitions from a static rigid structure to a dynamic compliant system that can adapt its mechanical properties during operation. The robot arm or end effector incorporates elements that allow controlled flexibility, enabling rapid positioning while absorbing force spikes through elastic deformation or controlled compliance during contact.
Solution Approach 2:
The patent changes physical parameters by adjusting the stiffness, damping, or mass characteristics of the contacting elements in real-time. Before contact, the system may increase stiffness for precise positioning; upon contact detection, it reduces stiffness or increases damping to limit force increases while maintaining positioning speed.
3Reliability
If a force-regulated system reacts to rapid disturbances, then contact force control is improved, but the regulated drive train has inertia which results in corresponding reaction time delay
Solution Approach 1:
The control system is segmented into multiple independent control loops operating at different levels. A fast outer loop handles rapid disturbances with minimal inertia, while a slower inner loop manages overall force regulation. This hierarchical segmentation allows the system to respond to high-frequency disturbances quickly without being constrained by the inertia of the main regulated drive train.
Solution Approach 2:
The patent introduces intermediary elements such as compliant mechanisms, springs, or damping elements between the robot drive train and the contact point. These intermediaries act as mediators that isolate the heavy regulated drive train from rapid disturbances, allowing the control system to react faster while the intermediary absorbs or attenuates high-frequency shocks and jerks.
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 apparatus enables jolt-free and jerk-free control of contact forces, reducing overshooting and impact energy, thus enhancing precision and reducing quality defects in machining and handling operations.
Implementation Method 1
at least one gearless actuator for positioning the holder in relation to the interface to the manipulator
Implementation Method 2
a restoring spring acting in opposition to the actuator force
Implementation Method 3
a restoring spring acting in opposition to the actuator force
Implementation Method 4
a sensor unit for directly or indirectly determining the force acting on the at least one actuator
Implementation Method 5
a closed-loop control unit which is configured to control the at least one actuator to press the holder at an adjustable minimum force (F0) against a stop
Data Source
AI summary
An apparatus for automated contact tasks and a related method are described. The apparatus includes a mechanical interface for connecting the apparatus to a manipulator, a holder for receiving a tool and being movable in relation to the mechanical interface, at least one actuator for positioning the holder in relation to the mechanical interface, a sensor unit that senses the actuator force provided by the at least one actuator, and a control unit that sets the actuator force to a desired minimum force to press the holder against a stop, while there is no contact between the tool and a surface, and detects contact when the holder moves in relation to the mechanical interface in opposition to the direction of the desired minimum force. The control unit further regulates the actuator force according to a pre-programmed contact force time-characteristic, when contact between the tool and the surface has been detected.