Stack Height Measurement Using RC Charging Correction
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Solution Overview
Problem
Existing devices for measuring the stack height of print media lack sensitivity, leading to inaccurate determinations due to interference from static charging and other disturbances.
Innovation Solution
A device and method that utilize a measuring capacitor with a control unit to measure charging and discharging times, applying correction variables based on the ratio of these times to improve accuracy, and incorporate a reference circuit for offset compensation to enhance measurement sensitivity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a simple capacitor-based measurement is used, then the device complexity is low, but the measurement precision is insufficient due to interference from static charging and disturbances
Solution Approach 1:
The measurement process is divided into distinct phases: charging phase with first reference voltage, discharging phase with second reference voltage, and correction phase. Each phase uses separate comparator configurations and reference voltages, allowing independent optimization and correction of measurement parameters to achieve high precision without requiring a single complex circuit design
Solution Approach 2:
The system employs feedback mechanisms where the control unit receives voltage change signals from the comparator, calculates charging and discharging times, determines correction variables based on the ratio of these times, and applies corrections to the measured stack height. This closed-loop feedback system continuously refines the measurement accuracy by compensating for disturbances such as static charging effects
2Reliability
If charging time measurement alone is used, then the measurement process is simple, but the reliability is low due to disturbances like static charging
Solution Approach 1:
The measurement system performs periodic charging and discharging cycles of the capacitor, with each cycle consisting of a charging phase (with first reference voltage) and a discharging phase (with second reference voltage). This periodic action allows the system to gather multiple time constants and calculate correction variables from the ratio of charging to discharging times, thereby improving reliability through statistical averaging and disturbance compensation
Solution Approach 2:
The system changes key parameters between charging and discharging phases: the reference voltage level (first reference voltage during charging, second reference voltage during discharging), the current direction (charging current vs. discharging current), and the measurement objective (charging time vs. discharging time). These parameter changes enable the system to isolate and correct for disturbances such as static charging effects by comparing measurements taken under different parameter conditions
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 significantly increases the sensitivity and accuracy of stack height measurements by correcting for disturbances and environmental influences, allowing for precise determination of stack height without intermediate corrections.
Implementation Method 1
a measuring capacitor (CM) with a first plate (CM1) and a second plate (CM2), the second plate (CM2) being connected to a reference potential
Implementation Method 2
the measuring resistor (RM) and the measuring capacitor (CM) form a first RC element
Implementation Method 3
a comparator (K) with a first input (K1) and an output (C), the first input (K1) being connectable to the output (VM) of the measuring amplifier (VM)
Data Source
Figure 1~2
Figure 3
AI summary
A device designed for measuring the stack height or thickness of a pressure medium by measuring charging times on a measuring capacitor, wherein the measuring capacitor has a first plate designed to receive pressure media and a second plate, wherein the first plate is connected to the reference potential, and a measuring circuit with a first RC element is provided, and a comparator and a control unit are provided, wherein the control unit is connected to the output of the comparator and to the first RC element, and the control unit applies a charging current to the first RC element at a first time and detects the first voltage change occurring at the output of the comparator at a second time in order to determine a charging time from the difference between the first time and the second time, wherein the control unit applies a first reference voltage to the comparator while the charging current is applied.and at a third time point, the RC circuit is subjected to a discharge current, and during the application of the discharge current, a second reference voltage is applied by means of the control unit, and at a fourth time point, a second voltage change occurring at the output of the comparator is detected in order to determine a discharge time and a first correction value from the ratio of the charging time and the discharge time from the difference between the third and fourth times, and to correct the charging time and/or the discharge time using the first correction value, and to determine the stack height or the thickness of the printing medium from a comparison of the corrected charging time and/or discharge time and a stored reference time.