Piezoelectric Force Sensor with Oblique Load Cells
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Solution Overview
Problem
Existing force and torque detection devices exhibit anisotropic sensitivity and limited natural frequency, particularly in the horizontal working plane, which restricts their application in high-speed machining processes.
Innovation Solution
The device employs piezoelectric load cells arranged at an angle to each other within the horizontal working plane, allowing both force components to be recorded via thrust and longitudinal effects, resulting in isotropic sensitivity and increased natural frequency through a more compact and lighter design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If piezoelectric load cells are arranged orthogonally in the horizontal working plane, then the device structure is simple and easy to manufacture, but the sensitivity becomes anisotropic with different sensitivity for different force components
Solution Approach 1:
The patent applies asymmetry by arranging piezoelectric load cells at oblique angles rather than orthogonal orientations. Specifically, load cells are positioned at angles α and β relative to the x-axis, where α ≠ β and neither equals 0° or 90°. This asymmetric angular arrangement transforms the anisotropic sensitivity caused by orthogonal positioning into isotropic sensitivity, enabling uniform detection performance across all horizontal force components while maintaining manufacturing feasibility through standardized angular configurations.
Solution Approach 2:
The patent changes the geometric parameter of load cell arrangement from orthogonal (0°/90°) to oblique angles (α, β). By adjusting these angular parameters, the patent achieves isotropic sensitivity in the horizontal plane. The specific angular values are selected to balance manufacturing ease with measurement performance, transforming the sensitivity characteristics without requiring complex non-standard angles that would complicate manufacturing.
2Measurement precision
If piezoelectric load cells are arranged to achieve isotropic sensitivity, then the sensitivity for all force components becomes uniform, but the device footprint and weight increase
Solution Approach 1:
The patent applies multi-functionality by designing each piezoelectric load cell to contribute to multiple measurement objectives simultaneously. The obliquely arranged load cells not only achieve isotropic sensitivity for horizontal force components but also inherently provide vertical force detection capability. This unified arrangement eliminates the need for separate orthogonal and vertical sensing systems, reducing the overall device footprint while maintaining isotropic horizontal sensitivity.
Solution Approach 2:
The patent transitions from two-dimensional orthogonal arrangement to three-dimensional oblique arrangement of load cells. By introducing vertical components to the load cell positioning, the system achieves isotropic sensitivity in the horizontal plane without expanding horizontal footprint. The vertical dimension provides the additional geometric relationship needed for uniform sensitivity while keeping the device compact in the horizontal working plane.
3Area of stationary object
If the device structure is made compact to reduce footprint, then the footprint area decreases, but the natural frequency is limited
Solution Approach 1:
The patent employs composite structural design combining rigid mounting platform material with piezoelectric sensor material in a integrated oblique arrangement. This composite configuration achieves high natural frequency (~6.5 kHz) within a compact footprint by optimizing the stiffness-to-mass ratio through the specific geometric arrangement and material selection, eliminating the trade-off between compact size and dynamic performance.
Solution Approach 2:
The patent optimizes the dynamic characteristics of the compact device by selecting oblique angles that maximize the natural frequency. The angular configuration α and β are chosen to create favorable stress distribution and structural rigidity, enabling the compact device to achieve natural frequency of approximately 6.5 kHz, which exceeds the 60,000 rpm spindle speed requirement while maintaining small footprint.
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
This configuration enhances the device's sensitivity and natural frequency, enabling effective force and torque detection in rotationally symmetric machining processes, particularly at higher spindle speeds.
Implementation Method 1
Each piezoelectric load cell A, B has piezoelectric sensors. The piezoelectric sensors are crystallographically oriented in such a way that a force acting on them generates electrical polarization charges.
Data Source
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AI summary
The invention relates to a device (1) for force and torque detection; comprising piezoelectric force measuring cells (A, B) which are mechanically biased in a horizontal working plane (XY) against end surfaces (81, 81') of a mounting platform (8) and detect power components (Fx, Fy, Fz); wherein at least one first end surface (81, 81') of the mounting platform (8) is disposed obliquely to at least one second end surface (82, 82').