Segmented Tactile Sensor for Incipient Slip Detection
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Solution Overview
Problem
Current robotic grippers lack the ability to accurately detect incipient slip and adjust grip force in real-time, leading to potential object loss during manipulation tasks, as existing tactile sensors require exploration before gripping, may experience gross slip before measurement, and struggle with continuous friction estimation.
Innovation Solution
A tactile sensor system with a contact surface featuring protrusions of varying heights, allowing for independent movement and three-dimensional force measurement, which detects incipient slip by differentiating tangential and normal forces across the contact interface, enabling timely grip force adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flat and contiguous surface is used for tactile sensing, then the sensor structure is simple, but the ability to detect incipient slip is limited due to inability to establish pressure differential and differential traction
Solution Approach 1:
The contact surface is segmented into multiple protrusions of varying heights rather than using a flat contiguous surface. This segmentation allows different regions to experience different normal forces and establish pressure differentials, enabling detection of incipient slip through differential traction measurements across the segmented contact elements.
Solution Approach 2:
Different protrusions are given different heights to create local variations in contact properties. The shorter protrusions experience higher normal forces and slip first, while taller protrusions experience lower normal forces and slip later, creating a sequence of slip events that provides information about friction and incipient slip.
2Reliability
If a contiguous elastomer sensing material is used, then the sensor structure is simple, but independence of movement between different localised regions is discouraged which further discourages occurrence of incipient slip
Solution Approach 1:
The contiguous elastomer material is segmented into discrete protrusions that can move independently. Each protrusion acts as an independent sensing element that can slip relative to the object surface, allowing the system to detect incipient slip events at multiple locations simultaneously.
Solution Approach 2:
The protrusions are designed to be flexible and capable of independent movement rather than being rigidly connected. This dynamic structure allows each protrusion to respond independently to tangential forces, enabling incipient slip to occur at different protrusions at different times based on their individual normal forces.
3Speed
If image processing of video stream is used to detect movement, then the sensor can be simple, but the sensing frequency is limited to relatively low frequency tactile events
Solution Approach 1:
The optical image processing system is replaced with a direct mechanical sensing approach using force sensors or piezoelectric elements that measure forces on each protrusion in real-time. This mechanical substitution enables high-frequency detection of slip events without the frame rate limitations of video cameras.
Solution Approach 2:
The protrusions themselves serve as both the sensing elements and the measurement mechanism. By instrumenting each protrusion with force sensors, the system directly measures the mechanical events of interest (slip forces) rather than inferring them from optical images, enabling higher frequency response.
4Measurement precision
If exploration of the object is required prior to gripping, then friction measurement can be obtained, but the manipulation time is increased
Solution Approach 1:
The sensor is pre-configured with protrusions of varying heights that create a built-in exploration mechanism. When the gripper contacts the object, the sequence in which protrusions slip provides immediate information about the friction coefficient, eliminating the need for separate exploration phases before gripping.
Solution Approach 2:
The friction measurement process is integrated into the continuous gripping action rather than being a separate preliminary step. The varying height protrusions ensure that slip events occur continuously during normal manipulation, providing ongoing friction estimates without interrupting the grasping task.
5Measurement precision
If normal and tangential forces are continuously monitored, then friction estimation can be provided, but the system complexity and measurement requirements increase
Solution Approach 1:
The force monitoring system is segmented into individual measurements on each protrusion rather than requiring simultaneous measurement of total normal and tangential forces on a flat surface. By measuring forces on multiple discrete protrusions with varying heights, the system can estimate friction from the sequence of slip events with simpler instrumentation.
Solution Approach 2:
The system changes the geometric parameter of protrusion height to create variations in normal force distribution. This parameter change allows friction estimation to be derived from the sequence of slip events across protrusions of different heights, reducing the need for complex simultaneous force measurements.
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 system effectively detects incipient slip and estimates friction, allowing for precise grip force modulation to maintain object security, improving dexterous manipulation in robotic and prosthetic grippers by providing continuous feedback and reducing the risk of object loss.
Implementation Method 1
a sensor arrangement for detecting displacement of at least three of the plurality of protrusions in three different dimensions to measure a three-dimensional force applied to the at least three of the plurality of protrusions
Implementation Method 2
the first contact surface region being configured to resist slip less than the second contact surface region
Data Source
Figure 1A~1C
Figure 2~3
Figure 4
AI summary
A system for assessing grip security, the system comprising: a contact surface having at least a first contact surface region and a second contact surface region, the first contact surface region being configured to resist slip less than the second contact surface region, a sensor for detecting slip in the first contact region.