Segmented Capacitive Capsule Weighing for Cap Detection Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing weight detection systems in pharmaceutical capsule filling machines face limitations such as reduced sensitivity, desensitization, common mode non-linearity, guard line instability, and complex zero-setting, especially when detecting the presence of capsule caps, which affects the accuracy of net weight measurement and cap identification.
Innovation Solution
A 'segmented' capacitive sensor with multiple detection segments and a charge amplifier configuration, where each detection stage is connected to a virtual ground, eliminating parasitic capacities and allowing independent detection of each capsule sector, thereby improving sensitivity and reducing mutual interference between electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional capacitive sensor with a single detection capacitor is used, then the device structure is simple, but the sensitivity is reduced and parasitic capacities affect measurement accuracy
Solution Approach 1:
The single detection capacitor is divided into multiple detection capacitors (Ct1, Ct2, ..., Ctn), each with its own detection electrode (S1, S2, ..., Sn) facing different sectors of the capsule. This segmentation allows independent measurement of different capsule portions while reducing the effect of parasitic capacities on each individual measurement, thereby improving overall measurement precision without requiring a single complex capacitor structure
2Measurement precision
If multiple detection electrodes are used to detect different capsule sectors, then the ability to detect cap presence and material distribution improves, but mutual interference between electrodes increases
Solution Approach 1:
Each detection electrode (S1, S2, ..., Sn) is positioned to face a specific sector of the capsule, creating localized detection zones. The guard electrodes (G1, G2, ..., Gn) are positioned adjacent to each detection electrode to confine the electric field locally. This local quality approach ensures that each electrode primarily senses its designated sector while minimizing electromagnetic interference with adjacent electrodes, enabling accurate cap presence and material distribution detection
3Stability of the object's composition
If guard lines are added to reduce parasitic input capacities, then measurement stability improves, but the circuit complexity and guard line instability increase
Solution Approach 1:
The guard function is segmented into multiple independent guard electrodes (G1, G2, ..., Gn), each associated with a specific detection electrode rather than using a single continuous guard line. This segmentation allows each guard electrode to be independently controlled and optimized for its local region, reducing the propagation of instabilities along a long guard line while maintaining electric field confinement and reducing parasitic capacities across the entire sensor array
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 enhances sensitivity, reduces noise, stabilizes the electric field, and allows precise detection of capsule caps and material distribution within capsules, improving the accuracy of weight measurement and cap presence detection.
Implementation Method 1
the weighing device 4 comprises a capacitive sensor consisting of a detection capacitor having a capacity Ct... During the rotation of the capsule-holding wheel 2, the capsule 1 is interposed between the first and the second plates 5a, 5b of the capacitive sensor, resulting in a capacitive variation ΔC of the detection capacitor Ct
Implementation Method 2
Each detection stage 14 is configured to convert the capacitive variation ΔC into an output voltage Vout... Each detection stage 14 comprises an operational amplifier 16, in a charge amplifier configuration
Data Source
AI summary
An electronic device for detecting the weight of a capsule for a pharmaceutical product is provided with: a plurality of detection electrodes, which face a respective one of a plurality of sectors into which the capsule is divided in a main extension direction thereof, each one of the detection electrodes forming a respective detection capacitor with a common plate defined by a capsule-holding element which holds the capsule; and an electronic circuit having a plurality of detection stages, each operatively coupled to a respective one of the detection electrodes so as to detect, in an independent and exclusive manner, a capacitive variation of the respective detection capacitor and to generate a respective output quantity, which is a function of the capacitive variation and indicative of the weight of the respective sector of the capsule.