Variable Current Drive Optical Sensor for ATM Banknote Detection
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Solution Overview
Problem
Existing optical sensors for detecting banknotes in ATMs require powerful and expensive light sources with high energy consumption, and their accuracy is affected by temperature changes, leading to increased costs and reduced reliability.
Innovation Solution
An optical sensor system using a variable current drive with a pulsing light source and a counter, coupled with a variable clock, which reduces thermal issues and improves accuracy by using a differential amplifier to achieve a linear relationship between media items and drive current, allowing for accurate counting of banknotes with reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a powerful LED light source is used to detect banknotes through high opacity media, then the detection capability is improved, but the energy consumption increases and heat generation requires expensive heat sinks
Solution Approach 1:
The patent applies periodic action by using pulsed LED illumination instead of continuous lighting. The LED is activated in periodic pulses during the banknote transport cycle, allowing the light source to remain dormant between measurements. This periodic operation dramatically reduces average power consumption while maintaining the peak intensity needed for detecting high-opacity media like banknotes, directly resolving the contradiction between detection capability and energy consumption.
2Measurement precision
If a powerful LED light source is used to detect banknotes through high opacity media, then the detection capability is improved, but expensive heat sinks are required to manage heat generation
Solution Approach 1:
By implementing periodic pulsed operation of the LED, the duty cycle is reduced significantly. The LED operates at high power only during brief measurement intervals and remains off during banknote transport and other operations. This temporal separation allows the thermal management system to dissipate heat between pulses, eliminating or reducing the need for expensive heat sinks while maintaining detection capability during active measurement periods.
3Illumination intensity
If the LED drive current is increased to overcome media opacity, then the light intensity increases, but the spectral response changes with temperature rise leading to reduced output intensity
Solution Approach 1:
The periodic pulsed operation allows the LED to operate at high current only during brief measurement windows, then cool down during transport intervals. This thermal cycling prevents sustained temperature rise that would cause spectral drift. Additionally, the system can measure the LED output intensity during each pulse and use this information to compensate for any temperature-induced variations, maintaining reliable detection thresholds despite temperature fluctuations.
Solution Approach 2:
The system incorporates feedback by measuring the actual LED output intensity during operation and using this information to adjust detection thresholds or compensation algorithms. This feedback mechanism accounts for temperature-induced spectral response changes, ensuring that the detection system maintains reliability and accuracy even as the LED temperature varies during pulsed operation.
4Reliability
If continuous illumination is used, then the light path is constantly monitored, but thermal problems associated with the light source increase
Solution Approach 1:
The system implements periodic illumination where the LED is activated only during brief measurement pulses during banknote transport. Between pulses, the LED remains off, allowing thermal dissipation and preventing continuous heat generation. The pulsed operation is synchronized with the banknote transport cycle, ensuring that measurements are taken at appropriate intervals while maintaining thermal management, thus resolving the contradiction between continuous monitoring and thermal control.
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 thermal problems and power consumption while maintaining accuracy in counting banknotes, even when they are superimposed, and can be integrated into self-service terminals with non-optical sensors for enhanced reliability.
Implementation Method 1
a variable current drive for energising the light source such that light intensity from the light source increases with increasing current... an optical receiver in communication with the variable current drive, and located on an opposite side of the transport path to the light source and aligned therewith to detect light output therefrom
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
An optical sensor (10) comprises: a light source (14) located on one side of a transport path (16); a variable current drive (22,24,26), an optical receiver (20) located on an opposite side of the transport path (16) to the light source ans aligned therewith to detect light output therefrom; and a memory (34). The variable current drive (22,24,26) is suitable for energising the light source (14) so that the light intensity from the light source (14) increases with increasing current. The variable current drive (22,24,26) includes (i) a drive circuit (24,26) for applying a pulse of current to the light source (14), during which pulse the light source is energised; and (ii) a counter (22) for increasing the amount of current applied by the drive circuit (24,26) during a pulse of current. The memory (34) may be arranged to store a value from the counter (22) indicative of a number of media items present in the transport path (16).