Weighing Chamber Closure Control Using Motion-Derivative Sensing
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Solution Overview
Problem
Weighing apparatuses, particularly those used for pipette calibration, face challenges in efficiently controlling the closure element to minimize disturbances during frequent filling operations, due to the need for precise and ergonomic actuation of the closure mechanism, which is often affected by aging and fouling of sensors.
Innovation Solution
A differentiating element is used to process the signal from a reflection sensor, calculating the first time derivative of the reflection intensity to distinguish between approaching and receding objects, allowing the control unit to control the motorized drive based on the direction of motion, thereby adapting to individual user sequences and reducing noise and fouling effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a closure element is provided to open/close the access port for pipette calibration operations, then accessibility for filling operations is improved, but frequent opening/closing causes excessive disturbances of the atmosphere in the weighing chamber
Solution Approach 1:
The closure element is made dynamically controllable through a motorized drive mechanism that responds to sensor signals. The system transitions from static manual operation to dynamic automated control, allowing the closure element to open only when a pipette is detected and close automatically when the pipette is removed, thereby minimizing unnecessary openings and reducing atmospheric disturbances.
Solution Approach 2:
A sensor system provides feedback about the presence of a pipette in the weighing chamber. This feedback signal is processed by control logic that automatically triggers the motorized drive to open or close the closure element, creating a closed-loop control system that responds to actual operational needs and prevents premature or unnecessary opening/closing actions.
2Extent of automation
If a non-contact switch in the form of a light barrier is used to detect pipette approach, then automation of closure element control is improved, but the operator is forced to execute the same sequence of motions including passing through the light barrier, which is ergonomically stressful
Solution Approach 1:
A reflective surface is introduced as an intermediary element that redirects sensor radiation onto the approaching pipette. This intermediary allows the sensor to detect the pipette's approach without requiring the operator to pass through the sensor's direct field of view, thereby maintaining automation while eliminating the ergonomic issue of forced motion sequences.
Solution Approach 2:
The detection system is configured to sense approach motion from multiple spatial dimensions or angles rather than requiring direct linear passage through a single-point sensor. This dimensional approach allows detection of pipette approach from various trajectories without forcing the operator to follow a predetermined path through the sensor beam.
3Ease of operation
If the closure element is controlled to open for each pipetting operation, then accessibility is maintained, but the requirement to initiate a command to open or close for each operation reduces productivity
Solution Approach 1:
The closure element control system operates autonomously by detecting the pipette's approach and automatically triggering the opening/closing sequence without requiring manual intervention. The system serves itself by using sensor detection to initiate the motorized drive, eliminating the need for operators to manually command each opening/closing action and thereby increasing productivity.
Solution Approach 2:
The closure element is positioned in advance and automatically opened as soon as the pipette approaches, rather than waiting for a manual command. This preliminary automated action ensures the access port is ready for immediate use, reducing delays between consecutive filling operations and improving overall throughput.
4Difficulty of detecting and measuring
If a reflection sensor is used to detect approaching objects, then non-contact detection is improved, but the reflective properties of different objects vary, making sensitivity range definition difficult and leading to faulty actuation
Solution Approach 1:
The sensor system parameters such as sensitivity threshold, detection range, and trigger conditions are optimized and adjusted based on the specific application requirements. By tuning these parameters, the system achieves reliable detection of pipettes while filtering out false signals from other objects with different reflective properties.
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
This solution ensures that the closure element is actuated only when necessary, reducing disturbances and maintaining ergonomic comfort by differentiating between user motions and static objects, and is resilient to aging and fouling processes.
Implementation Method 1
a reflection sensor with a radiation emitter for emitting sensor radiation, which can be reflected by a reflecting object, and with a radiation receiver for receiving a sensor radiation component reflected by the reflecting object
Data Source
AI summary
A weighing apparatus includes —a sample holder (20), —a protective housing (14, 16, 18) with an access port (181) and a closure element (26), —a reflection sensor (34) with a radiation emitter (37) emitting sensor radiation (38) reflected by a reflecting object (39) and with a radiation receiver (42) receiving a sensor radiation component (40), reflected by the object and —a control unit (32), connected to a motorized drive (30) of the closure element and to the reflection sensor, and which controls the motorized drive with a reflection sensor signal, for transferring the closure element between closed and open positions. A differentiating element subjects a sensor primary signal (52) of the reflection sensor to a differentiation. The primary signal depends on a reflection intensity of the reflected radiation component and generates a sensor secondary signal (60). The control unit controls the motorized drive based on the sign of the secondary signal.