Magnetic Piston Rod Force Sensing Without Sensor Overload
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Solution Overview
Problem
Existing cylinder-piston units with integrated force sensors face challenges such as mechanical overload susceptibility, complex integration, and inaccurate force measurement due to non-homogeneous magnetic properties of ferromagnetic piston rods, which complicates reliable force detection for safety-critical applications like work machines.
Innovation Solution
A non-contact magnetic force measurement system using a ferromagnetic piston rod with external magnetic sensors and an evaluation unit that stores position-dependent calibration values to determine forces accurately, allowing for robust and simple implementation by avoiding direct power and signal routing within the cylinder-piston unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a force sensor is integrated in the piston rod or support base, then force measurement capability is achieved, but the sensor is exposed to high mechanical loads and susceptible to overload
Solution Approach 1:
The patent uses the ferromagnetic piston rod as an intermediary carrier of magnetic properties rather than placing a force sensor directly in the mechanical force flow. The magnetic sensor on the guide piece detects force-induced changes in the piston rod's magnetic properties indirectly, keeping the sensor isolated from direct mechanical loads while still enabling force measurement through magnetic field interactions.
2Measurement precision
If a force sensor is integrated in the piston rod, then force measurement is enabled, but integration becomes complex and error-prone due to routing of power and signal lines
Solution Approach 1:
The force measurement function is extracted from the moving piston rod assembly and relocated to the stationary guide piece. The magnetic sensor is mounted on the guide piece, which remains stationary relative to the cylinder housing, thereby eliminating the complexity of routing power and signal lines through moving seals and joints while still enabling force detection on the piston rod.
3Device complexity
If non-contact magnetic measurement is used on the longitudinally displaceable piston rod, then sensor integration is simplified, but measurement accuracy decreases due to non-homogeneous magnetic properties
Solution Approach 1:
The patent applies local quality by creating a homogeneous magnetic test section in a specific region of the piston rod. A magnetic test piece with uniform magnetic properties is integrated into the piston rod at the measurement location, ensuring that the magnetic sensor detects only force-induced changes rather than variations due to material non-homogeneity elsewhere in the rod.
4Measurement precision
If magnetic sensors are arranged on the moving piston rod, then force measurement is possible, but power and signal routing becomes complicated
Solution Approach 1:
Instead of placing the magnetic sensor on the moving piston rod as conventionally done, the patent inverts the arrangement by mounting the magnetic sensor on the stationary guide piece while placing a magnetic test piece on the moving piston rod. This inversion allows the sensor to remain stationary with fixed power and signal connections, while still detecting force changes through the magnetic interactions of the moving test piece.
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 provides accurate and robust force measurement, enhancing safety and reliability by simplifying sensor integration and power supply, while improving resistance to mechanical overload and environmental influences.
Implementation Method 1
the measuring sensor being designed as a non-contact magnetic sensor which detects a load-dependent change in a magnetic property of the ferromagnetic material
Data Source
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AI summary
A cylinder-piston assembly comprises a working cylinder and a longitudinally displaceable piston, which is sealed within the working cylinder and carries a piston rod at least on one side. The piston rod extends from the working cylinder at its end opposite the piston. The piston rod is made, at least in part, of a ferromagnetic material. A measuring system, which interacts with the piston rod, is provided to detect a force acting on it. This system includes at least one measuring sensor, designed as a non-contact magnetic sensor, which detects a load-dependent change in a magnetic property of the ferromagnetic material.