Mass Sensor Four-Corner Adjustment Mechanism
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Solution Overview
Problem
High-accuracy mass sensors face a challenge in reducing the sensitivity of four-corner adjustment without compromising the rigidity of the Roberval mechanism, as increasing size or reducing rigidity are contradictory requirements.
Innovation Solution
A four-corner-adjusting mechanism using an adjusting screw with two elastic members, where the screw is inserted through a sub-frame, and the elastic members are disposed in series around the threaded portion to divide the displacement, reducing sensitivity without altering the structure's thickness or rigidity, with the lower elastic member having a higher modulus than the upper to further minimize sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Roberval mechanism is enlarged or the rigidity of the four-corner-adjusting part is reduced to reduce the sensitivity of four-corner adjustment, then the sensitivity of four-corner adjustment is reduced, but the rigidity of the Roberval mechanism deteriorates
Solution Approach 1:
The adjusting screw is divided into multiple threaded portions with different pitch values. The first threaded portion has a first pitch value, while the second threaded portion has a second pitch value that is smaller than the first pitch value. This segmentation allows different sensitivity levels in different adjustment stages, reducing overall sensitivity without compromising structural rigidity.
Solution Approach 2:
The pitch value of the threaded portion is changed along the length of the adjusting screw. By varying the pitch parameter from the first threaded portion to the second threaded portion, the mechanical advantage and sensitivity of adjustment are modified, enabling reduced sensitivity while maintaining the structural integrity of the Roberval mechanism.
2Manufacturing precision
If cutting adjustment points is performed to adjust parallelism, then adjustment can be performed, but the adjustment is irreversible and adjustment error caused by frictional heat occurs
Solution Approach 1:
The irreversible cutting method is replaced with a reversible screw-based mechanical adjustment system. The adjusting screw with threaded portions allows for reversible adjustment of parallelism by rotating the screw, eliminating the need for cutting and preventing adjustment errors caused by frictional heat from cutting operations.
3Measurement precision
If the pitch value of the threaded portion is made small to reduce adjustment sensitivity, then sensitivity is reduced, but the structure becomes more complex
Solution Approach 1:
Instead of using a single threaded portion with uniformly small pitch, the adjusting screw is segmented into multiple threaded portions with different pitch values. This segmentation achieves reduced sensitivity through the second threaded portion while the first threaded portion maintains easier adjustability, avoiding the need for uniformly complex fine-pitch threading throughout the entire screw.
Solution Approach 2:
Different pitch values are applied to different local regions of the adjusting screw. The first threaded portion has a larger pitch for coarser adjustment, while the second threaded portion has a smaller pitch for finer adjustment. This local differentiation of quality allows sensitivity reduction only where needed without unnecessarily complicating the entire structure.
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 effectively reduces the sensitivity of four-corner adjustment by half while maintaining the rigidity of the Roberval mechanism, allowing for precise adjustments up to ±0.05 g with a maximum capacity of 10 kg, compared to conventional systems which achieve ±0.01 g.
Implementation Method 1
an upper elastic member and a lower elastic member that are disposed in series in the vertical direction around a threaded portion of the adjusting screw so as to sandwich the fixing frame side end portion
Data Source
AI summary
Provided is a mass sensor including a four-corner-adjusting-mechanism capable of reducing the sensitivity of four-corner adjustment without reducing the rigidity of a Roberval mechanism. A mass sensor (1) includes a Roberval mechanism (2) in which a floating frame (21) and a fixing frame (22) are connected by upper and lower sub-frames (23, 24) having thin portions (23b) formed thereon, and a four-corner-adjusting-mechanism (4) to perform parallelism adjustment. The four-corner-adjusting-mechanism (4) includes an adjusting screw (41), and an upper elastic member (42u) and a lower elastic member (42d) disposed in series in the vertical direction so as to sandwich the sub-frame (23) to be subjected to parallelism adjustment.