Core Summary
When equipment requires real-time measurable piston position and participates in closed-loop control, conventional cylinders equipped with external wire displacement meters often suffer from cumbersome wiring, difficult protection, and susceptibility to damage in oil mist environments. Conforti's TD/TK/TH/TX/TP servo hydraulic cylinders incorporate magnetostrictive position sensors built into the piston rod, offering non-contact position measurement, high accuracy, and long lifespan. To ensure optimal performance, several aspects need to be aligned in advance, from model selection to commissioning.
1. When is position feedback needed
Closed-loop pressing and synchronous lifting
For hydraulic pressing equipment, it is necessary to switch the pressure curve based on the position of the piston, or ensure consistent displacement among multiple cylinders during synchronous lifting and lowering. In these scenarios, position is the control variable, rather than merely observing the position signal. External displacement meters can provide signals, but the cable mechanism outside the cylinder is exposed to oil mist and vibration over extended periods, leading to a higher failure rate.
Real-time positioning is more stable than a proximity switch
A standard magnetic switch can only provide a binary output of "present/absent". In contrast, a servo cylinder outputs continuous position values. The controller can perform PID adjustments, soft landing, and error compensation, significantly enhancing the consistency of the finished product.
II. Principle of Servo Cylinder (Magnetostriction)
Contactless positioning
The magnetostrictive sensor is arranged along the axis inside the piston rod, with the magnetic ring on the piston following suit. The controller sends out an interrogation pulse, which propagates along the waveguide wire and intersects with the magnetic field of the magnetic ring, generating a strain pulse. The real-time position is calculated based on the return time. The entire process involves no mechanical contact, making it less prone to wear.
Real-time location, no loss in case of power failure
The sensor outputs real-time position values, and the current position can be read immediately upon power-up, eliminating the need to return to zero or find a reference point. This is particularly advantageous for processes that require mid-way pauses and resumption.
III. Selection Key Points
Select series based on circuit pressure
The TD/TK is 160 bar, TH/TX is 210 bar, and TP is 250 bar. First determine the circuit pressure, and then select the cylinder bore (40–200 mm) from the corresponding series. Inform the supplier of the peak pressure to avoid using low-pressure series in high-pressure circuits.
Confirm signal interface
Common outputs of magnetostrictive sensors include analog signals (such as 0–10 V, 4–20 mA) and industrial buses (such as SSI, Profibus, CANopen). The type of output supported on the controller side should be determined when ordering, otherwise adding a conversion module later will not only occupy space but also increase failure points.
Installation and Rod End
Servo cylinders are more sensitive to the coaxiality and lateral forces of the piston rod. During installation, it is essential to ensure that the cylinder axis aligns with the direction of the load movement, and to avoid generating bending moments at the rod end connection, as this can affect the sensor's lifespan and reading stability.
IV. Interface with PLC
Range and Calibration
Match the sensor range with the PLC engineering quantity, for example, a cylinder stroke of 500 mm corresponds to 4–20 mA or 0–27648 counts. Calibration is completed under no-load conditions, and the zero point and full-scale values are recorded for future maintenance reference.
Filtering and Sampling
The hydraulic system experiences pressure fluctuations, and it is recommended to apply moderate filtering to the position signal. However, excessive filtering can slow down the response. It is advisable to first test a set of parameters on a laboratory bench and then transfer them to the field, which saves time compared to directly debugging on the machine.
V. Debugging Considerations
Upon power-up, first read the real-time position to confirm its consistency with the mechanical zero point
Repeat the full stroke several times and observe whether the readings follow the movement and if there are any jumps or changes
When maintaining pressure under load, observe the position drift. If it exceeds the tolerance, check the installation coaxiality
For bus-type systems, pay attention to terminal resistance and address. For analog signals, ensure proper shielding and grounding
Parameter Table (Comparison of Servo Cylinder Series)
> The above is the conceptual approach to the solution. Specific models and signal interfaces are subject to the original Conforti documentation. QN TECHNOLOGY can assist in verifying the sensor output type and PLC interface solution.
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