Indentation Head Servo Control for High-Dynamic Force Measurement
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Solution Overview
Problem
Existing indentation systems are bulky, complex, and unsuitable for high dynamic force measurements due to significant mass and require multiple tips for accurate force determination, limiting precision and flexibility.
Innovation Solution
An indentation head system with a zero-level sensor, elastic element, and actuator arrangement that maintains a quasi-infinite stiffness through servo control, allowing independent measurement of indentation depth and force, and minimizes inertia for high dynamic force applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an elastic element is connected in series with the indenter tip to measure force, then force measurement capability is improved, but the mass of the indenter tip increases significantly
Solution Approach 1:
The patent replaces the traditional mechanical series connection of elastic element and indenter tip with a parallel arrangement where the elastic element is connected between the indenter tip and a piezoelectric actuator. The measurement system uses capacitive sensors to detect displacement of the indenter tip and actuator, converting mechanical measurements into electrical signals for processing. This substitution reduces the mass of the indenter tip assembly while maintaining force measurement capability through the elastic element's deformation measurement.
2Measurement precision
If a capacitive sensor measures displacement of the indenter tip, then measurement precision is improved, but the system becomes bulky and complex
Solution Approach 1:
The patent combines multiple measurement functions into a unified capacitive sensing system. The same capacitive sensor technology is used to measure both the displacement of the indenter tip relative to the reference element and the elongation of the piezoelectric actuator. By merging these measurement functions into a single integrated system rather than using separate sensor assemblies, the patent reduces overall system complexity and size while maintaining high measurement precision for both indentation depth and force.
3Measurement precision
If the indenter tip is arranged mechanically in series with an elastic element, then force measurement is enabled, but the inertia of the tip increases, reducing suitability for high dynamic force measurements
Solution Approach 1:
The patent transitions from a static mechanical series arrangement to a dynamic parallel configuration where the indenter tip and elastic element are connected in parallel with a piezoelectric actuator. This dynamic arrangement allows the system to respond rapidly to changing force conditions because the capacitive sensors can detect tip displacement in real-time, and the piezoelectric actuator can quickly adjust to maintain measurement accuracy. The parallel configuration reduces the effective inertia of the measuring system compared to a series arrangement, enabling high dynamic 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
Improves indentation measurement accuracy and precision by maintaining constant relative position, enabling independent depth and force measurement, and supports high dynamic force applications with minimized inertia.
Implementation Method 1
an elastic element, such as a linearly-acting spring (e.g. a coil spring), blade flexure or similar, connected between said indenter tip and an actuator (which is typically but not exclusively a piezoelectric actuator)
Implementation Method 2
an elastic element, such as a linearly-acting spring (e.g. a coil spring), blade flexure or similar, connected between said indenter tip and an actuator
Implementation Method 3
said controller being furthermore adapted to calculate a force applied by said indenter tip to said sample on the basis of said known elongation of said actuator and an elastic coefficient of said elastic element, e.g. on the basis of Hooke's Law
Implementation Method 4
a zero-level sensor arranged to output a signal indicating whether said indenter tip is displaced with respect to said reference element from a neutral relative position
Data Source
Figure 1
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AI summary
Indentation head system (1) for an indentation instrument (100), comprising: - an indenter tip (3) adapted to be brought into contact with a surface of a sample (5) along at least an indentation axis (A); - a reference element (9) arranged to support said indenter tip (3). According to the invention, said indentation head system (1) further comprises: - a zero-level sensor (17) arranged to output a signal indicating whether said indenter tip (3) is displaced with respect to said reference element (9) from a neutral relative position, considered along said indentation axis (A); - an elastic element (19) connected between said indenter tip (3) and an actuator (21) with known elongation, said actuator (21) being connected to said reference element (9); - a controller (25) adapted to receive signals from said zero-level sensor (17) to carry out servo control of said actuator (21) based on output of said zero-level sensor (17) and said known elongation of said actuator (21) such that said zero-level sensor (17) outputs a signal corresponding to a substantially zero displacement of said indenter tip (3) from said neutral relative position, said controller furthermore being adapted to calculate a force applied by said indenter tip (3) to said sample (5) on the basis of an output of said displacement sensor (23) and an elastic coefficient (k) of said elastic element (19).