Composite Weigh Plate with Offset Slits for RF Interference
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Solution Overview
Problem
The stainless steel weigh plate in checkout systems interferes with security tag deactivation systems, causing signal attenuation and compromising the accuracy of low-profile, high-sensitivity weigh scales due to reduced stiffness and potential side loading of load cells.
Innovation Solution
A composite weigh plate with a stainless steel face plate and metal sub-frame, featuring offset slits to prevent a closed conductive loop, supported by an electrically non-conductive bonding agent like VHB™ Tape to maintain structural integrity and avoid interference with deactivation systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a stainless steel weigh plate is used, then the plate is easy to clean and pleasing to the eye, but the plate creates a closed loop that disrupts eddy currents and attenuates the signal range of the deactivation system
Solution Approach 1:
The weigh plate is divided into two separate components: a stainless steel face plate and a metal sub-frame. This segmentation breaks the closed loop conductive path that causes eddy current disruption, allowing the deactivation system to function properly while maintaining the aesthetic and cleaning properties of stainless steel.
Solution Approach 2:
A non-conductive bonding agent is introduced as an intermediary material between the face plate and sub-frame. This bonding agent electrically isolates the two metal components, preventing the formation of a closed loop while still providing mechanical support and structural integrity.
2Object-affected harmful factors
If the metal frame of the weigh plate is split to avoid interference with deactivation systems, then the deactivation system works properly, but the stiffness of the weigh plate is compromised causing deflection and weighing errors
Solution Approach 1:
The weigh plate uses a composite construction combining a stainless steel face plate with a metal sub-frame, bonded together with a non-conductive bonding agent. This composite structure maintains the necessary stiffness and structural integrity while the segmented design prevents closed loop formation, resolving both the deactivation interference and strength requirements.
3Object-affected harmful factors
If a composite structure with non-metallic support is used, then the closed loop is avoided, but the reduced stiffness causes deflection under load and side loading of load cells
Solution Approach 1:
The patent employs a composite structure where a metal sub-frame provides the necessary structural support and stiffness, while a non-conductive bonding agent connects it to the stainless steel face plate. This combination avoids closed loop formation and maintains weighing accuracy by preventing deflection under load.
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 ensures structural integrity and accurate weighing without disrupting security tag deactivation, maintaining the performance of high-sensitivity scales by preventing closed loop conductive paths and minimizing deflection.
Implementation Method 1
a deactivation system having an antenna for transmitting a signal to the security feature
Implementation Method 2
the metal frame of the weigh plate is split around the window 18... the weigh plate creates a closed loop that disrupts the eddy currents of the magnetic pulse generated by the deactivation system
Data Source
AI summary
A checkout station comprises a deactivation system having an antenna for transmitting a signal to the security feature on a product passing over the checkout station to deactivate the security feature and a scale for weighing the product at the checkout station. A composite weigh plate is supported by the scale and includes a metal face plate configured to support the product thereon for weighing the product and a metal sub-frame configured to support the face plate. The face plate and the sub-frame each define a slit so that they do not form a closed electrically conductive loop. An electrically non-conductive bonding agent fixes the metal face plate to the metal sub-frame to maintain the structural integrity of the composite weigh plate in spite of the presence of the slits in the metal components.