Position and pressure sensors for spring making machine
Learn how to achieve 0.1 mm repeatability for high speed bending tools in spring making machines
In order to produce springs of the desired shape and dimension, it is essential to be able to control the radius of curvature of the spring circumference
With WPA-S magnetostrictive position and KS pressure sensors it is possible to control:
- the oil pressure of the hydraulic circuits;
- in real time the position of the bending tools with 0.1 mm repeatability thanks to the SSI synchronized digital output.
Overview
- Application: Spring production machine requiring repeatability of 0.1 mm for its bending tools at a high sampling frequency
- Product: WPA-S Magnetostrictive transducer – 125-400 mm stroke – aluminium profile
- Results: WPA-S enabled the repeatability required – thanks to a resolution of 5 𝜇m with the position sampling updated every 500 𝜇s (2 kHz).
The process
In order to produce springs of the desired shape and dimension, it is essential to be able to control the radius of curvature of the spring circumference.
Spring physics demand at least three points to coil wire and the mechanical control is translated in the movement of up to four bending tools (Figure 1), driven by a hydraulic circuit.
By coordinating their relative positions, three of them bend a sliding cylindrical wire, giving it the typical “spring” shape.
When the desired length is reached, the fourth tool cut the spring.
The challenge
A constant radius of curvature and hence a high-quality product can only be ensured by the perfect coordination of the bending tools.
For this reason, it is necessary to control the position of bending tools with a repeatability of 0.1 mm and at the same time a low linearity error on the measurement.
Additionally, the process speed requires the position control to be highly responsive – right from data sampling to its transfer to the PLC.
The consequence is that the position sensors cannot be connected to a fieldbus line but they must send the data directly to the control PLC.
Last but not least, since the bending tools are moved by hydraulic cylinders, a precise control of the oil pressure of the hydraulic circuit is essential.
Product benefits
WPA-S Magnetostrictive Position Transducer
- WPA-S Magnetostrictive transducers with a signal linearity error ≤ ±0.01% FS, gives a highly repeatable positioning control up to 0.1 mm
- With the position sampling frequency of 2 kHz, equal to a reading update every 500 𝜇s, it is possible to monitor and control the position of the bending tools in real-time
- SSI 25-bit Gray code, synchronized digital output for a direct transmission to the PLC
KS Pressure Transducer
- High accuracy and fast response time of KS transmitter provide a perfect pressure measurement of the hydraulic circuit.
Solution
Position control of the bending tools:
WPA-S Position Transducers (profile) – 4 Nos
- Transducer stroke/material: 125-400 mm, profile in aluminium
- Signal linearity (error): ≤ 0.01 % FS
- Position sampling frequency: 2 kHz
- Output: SSI synchronized digital output, 25 bit, Gray code
Oil pressure of the hydraulic circuit:
KS pressure transducer – 1 No
- Extremely robust with SIL2 safety certification as standard
- Accuracy: < ± 0.5 % FS
