Telemetric Load Cell with Inductive Coupling for Rotating Screw
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Solution Overview
Problem
Existing load cells in plastic injection molding machines face challenges in accurately measuring injection forces due to friction losses from gears and bearings, requiring custom designs and leading to downtime for replacement when damaged, as they cannot directly attach behind the rotating screw and measure torsional forces simultaneously.
Innovation Solution
A telemetric load cell with radio transmission of signals, featuring a load cell body with strain gauges and an amplifier that rotates with the screw, using inductive coupling for power and signal transmission via a primary and secondary coil, allowing simultaneous measurement and transmission of injection and torsional forces without lateral gear drives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If load cells are attached directly behind the rotating screw to measure injection force, then measurement precision is improved, but the connection cables would wind up during rotation causing reliability issues
Solution Approach 1:
The patent replaces the mechanical connection cable system with an inductive coupling system. A primary coil arranged axially above the load cell generates a magnetic field that inductively couples to a secondary coil in the load cell, eliminating the need for physical connection cables that would wind during screw rotation. This substitution of mechanical connection with electromagnetic coupling resolves the reliability issue while maintaining measurement precision.
Solution Approach 2:
The patent introduces an intermediary magnetic field as a mediator between the stationary measurement system and the rotating load cell. The primary coil in the stationary housing generates a magnetic field that penetrates the air gap to inductively couple with the secondary coil in the rotating load cell body. This magnetic field intermediary enables power and signal transmission without direct mechanical contact, solving the cable winding problem.
2Measurement precision
If custom dimensioned load cells are developed for each machine type, then measurement accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent designs a universal load cell system with standardized dimensions and mounting interfaces that can be applied across different machine types. The load cell body, primary coil arrangement, and inductive coupling system are configured to work with various screw diameters and machine configurations through adjustable parameters rather than custom designs. This universality reduces device complexity and manufacturing costs while maintaining measurement accuracy through the standardized inductive coupling mechanism.
3Reliability
If load cells are positioned away from the screw to avoid rotation issues, then reliability is improved, but friction losses from gears and bearings falsify the measurement
Solution Approach 1:
The patent replaces mechanical connection methods with inductive coupling to enable the load cell to be positioned directly behind the rotating screw. The primary coil in the stationary housing inductively couples to the secondary coil in the rotating load cell, eliminating the need for mechanical connections that would interfere with the measurement. This allows the load cell to be in the optimal measurement position without the friction losses from gears and bearings affecting the measurement, as the inductive coupling transmits power and signals without mechanical contact.
4Ease of manufacture
If the entire load cell must be replaced upon damage, then manufacturing simplicity is maintained, but loss of time increases during maintenance
Solution Approach 1:
The patent segments the load cell system into modular components, particularly the load cell body that can be independently replaced from the stationary housing containing the primary coil. This modular design allows the rotating load cell body to be removed and replaced without replacing the entire system, reducing maintenance time and downtime while maintaining manufacturing simplicity through standardized modular components.
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
Enables precise, continuous measurement of injection and torsional forces directly on the screw, reducing friction losses and enabling standardized designs, with the ability to transmit signals wirelessly, thus improving process control and reducing downtime for maintenance.
Implementation Method 1
the feed module containing the primary coil and the pick-up ring containing the secondary coil of the inductive coupling
Data Source
Figure 1
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AI summary
The telemetric load cell (1) for electrically measuring negative and positive injection forces (F) in injection molding machines is provided directly behind the rotating screw (2), and the integrated amplifier (10) and the radio module (11) are supplied in a radial direction via a stationary supply module (8) and via a pick-up ring (9) which is arranged on the outer side of the load cell body.