Precise displacement measurement of thrust cylinders in tunnel boring machines

Tunnel boring machines (TBMs) are highly complex, fully automated systems that work their way through soil and rock with enormous precision in order to create traffic and supply tunnels for roads, railways, water pipes or power lines. The construction of a tunnel takes place in stages: The machine is braced against already installed tubbings by massive hydraulic cylinders and pushes itself forward while the drilling tool simultaneously removes material from the tunnel face. Tubbings are prefabricated components that form the outer shell of a tunnel and must be manufactured with millimetre accuracy. Monitoring the thrust process in TBMs is crucial, as even the smallest deviations in the millimetre range can have significant impacts on tunnel geometry over hundreds of metres.

This technology plays a key role, especially in countries with advanced infrastructure development such as China, which has more than half of all the tunnel boring machines in use worldwide. Estimates suggest that there are currently more than 3,000 tunnel boring machines in operation worldwide, many of which are used in the transport and energy sectors. Tunnels are essential to the global economy, as they shorten transport routes, secure supply chains and relieve urban infrastructures. Without precise measurement technology in the thrust systems, today’s highly automated tunnel construction would hardly be feasible on this scale and with this accuracy.

In tunnel construction, the precise measurement of the cylinder movement in tunnel boring machines therefore plays a central role, as the tunnel boring machine is advanced via hydraulic thrust cylinders. Their exact stroke must be continuously monitored in order to ensure uniform advance, control loads and detect deviations in the alignment at an early stage. The GX200 draw wire sensor from WayCon Positionsmesstechnik GmbH is particularly suitable for this task, as it combines a robust design with high measurement accuracy and industrial interface diversity.

The GX200 operates on the principle of linear displacement measurement. A stainless steel cable is pulled out of the housing as the thrust cylinder moves; this linear movement is detected by an internal measuring system and converted into an analogue or digital position signal. Thanks to its robust construction, the sensor can be mounted directly on the hydraulic cylinder or in its immediate vicinity. The cable end is attached to the moving part of the cylinder, while the housing is fixed in place. In this way, every stroke is recorded precisely and proportionally. Furthermore, deflection mechanisms enable flexible integration even in confined spaces and ensure continuous cable guidance.

Distance measurements of up to twelve metres with linearity deviations of a maximum of 0.1 percent are standard for the GX200 draw wire sensor. This makes it possible to reliably detect even the smallest movements in the millimetre range. The high dynamics with short response times enabled by analogue technology allow for precise detection of rapid feed movements. A particularly advantageous feature is the sensor’s high mechanical load capacity. The housing and cable guide are designed for harsh operating conditions and achieve protection classes up to IP69K. The GX200 is designed for heavy-duty applications, such as those encountered in tunnel boring with rock abrasion, and is especially resistant to shock and vibration.

The GX200 draw-wire sensor is available with various output signals for position measurement, including potentiometer output, voltage and current output, as well as a digital CANopen interface. The digital version offers a resolution of up to 16 bits at a measurement rate of 1 kilohertz, which facilitates integration into modern control systems and reduces susceptibility to interference. Optionally, redundant output signals can be implemented in both the analogue and digital versions to increase measurement reliability in applications where safety is crucial.

Use in tunnel environments places high demands on material and measurement stability. Dust, moisture, dirt and temperature fluctuations have a direct impact on the sensor system. The GX200 is designed for operating temperatures from minus 40 to plus 85 degrees Celsius and features a low temperature coefficient, which minimises the thermal effects on measurement accuracy. The stainless steel cable is corrosion-resistant and, when properly guided, can achieve a long service life. Regular maintenance of the cable guide and inspection for wear ensure long-term measurement stability.

For the stroke measurement of thrust cylinders in tunnel boring machines, the GX200 draw wire sensor thus combines high precision with mechanical robustness. Its flexibility with regard to installation and signal processing makes it a reliable solution for the demanding conditions in tunnel construction. Through the combination of compact design, robust mechanism and precise displacement measurement, the sensor makes a significant contribution to the process reliability and efficiency of modern tunnel boring systems.

For technical information about the GX200 draw wire sensors, please visit the data sheet GX200.
You can find our selection of draw wire sensors on our product page for draw wire sensors.