Cash Till Load Cell Stabilization to Reduce Jitter and Drift
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Solution Overview
Problem
Cash till load cells suffer from random fluctuations ('jitter') and gradual changes ('drift') in signals, leading to incorrect calculations of cash amounts, and are unable to differentiate between different denominations of coins or notes, resulting in inaccurate monitoring of transactions.
Innovation Solution
A method that stabilizes load cell readings by storing verified values within predetermined thresholds, calculating an average over time to reduce jitter and drift effects, and using threshold values to determine changes in coin or note quantities, while only taking readings when the till drawer is closed to minimize errors and conserve resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If load cell readings are taken continuously to monitor cash amounts, then monitoring reliability is improved, but jitter and drift cause measurement precision to deteriorate
Solution Approach 1:
The system performs preliminary stabilization by taking multiple readings and calculating an average value before using it for cash amount determination. This preliminary action filters out jitter and drift effects, ensuring that the reference value used for monitoring is stable and accurate, thus resolving the contradiction between continuous monitoring reliability and measurement precision
Solution Approach 2:
The system implements feedback by comparing successive readings and determining whether they are stable (within a threshold) before accepting them as verified values. This feedback mechanism ensures that only reliable, stable measurements are used, maintaining both monitoring reliability and measurement precision by dynamically adjusting when readings are accepted based on their stability
2Measurement precision
If multiple readings are taken and averaged to reduce jitter and drift, then measurement precision is improved, but processing time increases
Solution Approach 1:
The system takes a limited number of readings (exactly 10) rather than continuously, which is sufficient to achieve the desired measurement precision while avoiding excessive processing time. This partial action approach balances the need for accurate averaging with the constraint of time efficiency
Solution Approach 2:
The system performs reading stabilization periodically by taking 10 readings at scheduled intervals rather than continuously. This periodic action reduces the overall processing time while still achieving measurement precision by averaging multiple readings at each periodic interval, thus resolving the contradiction between precision and time loss
3Productivity
If readings are taken while the drawer is open to enable real-time monitoring, then monitoring coverage is improved, but measurement precision deteriorates due to external disturbances
Solution Approach 1:
The system applies preliminary anti-action by detecting when the drawer is open and preventing readings from being taken during that state. This anticipatory measure blocks external disturbances (such as air currents and vibrations) before they can affect the measurements, thus maintaining measurement precision while still providing monitoring coverage when the drawer is closed
Solution Approach 2:
The system extracts and removes readings taken when the drawer is open from the set of valid readings. By separating and excluding these potentially inaccurate readings, the system ensures that only readings taken under stable conditions (drawer closed) are used for cash amount determination, thus maintaining measurement precision while preserving monitoring coverage during closed states
Data Source
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AI summary
A cash till having a drawer (2) with a plurality of compartments (4) for storing coins, notes or vouchers. Each compartment (4) has an associated load cell (6), which produces a signal that is proportional to the weight of the compartment contents. The signal is provided to a monitoring apparatus (10) that takes readings from the load cell (6) whilst the till drawer (2) is closed. If a preceding reading is within a threshold amount of the current reading, then the preceding reading is stored as a verified value. The method removes jitter and drift in the signals produced by the load cells (6) of the cash till.