Drives and Controls Magazine
Inductive system reads absolute linear positions to 4m
Published:  12 May, 2016

Rexroth has developed a robust linear measuring system that reads absolute positions inductively to an accuracy of 4m similar to that of glass scales. The company is building the IMS-A system into its linear guides, thus avoiding the need for external measurement or air purge systems. It says that the system is immune to contamination, vibrations, shocks and magnetic interference and needs no buffer batteries in the event of a power failure.

Turning automated machinery back on after a power failure can cause problems. In many applications, the controller needs to know the position of each axis immediately. Incremental measuring systems need to complete a reference run to obtain this information, extending ramp-up times and possibly damaging workpieces and tools.

The new measuring system recognises the absolute position of an axis as soon as a machine is switched on and reports this to the controller without needing to perform a reference run. It does this without using buffer batteries that would need regular replacement.

Because of its inductive measuring principle, the IMS-A operates without physical contact and is thus wear-free. It is not affected by external magnetic fields allowing it to be used with linear motors, for example or by vibrations of up to 10G and shocks up to 50G.

Because the sensors and evaluation electronics are located in a protective housing on the end-face of the runner block, their performance is not affected by dirt, coolants or other contaminants. They do not need high-maintenance, energy-consuming air-purge systems either. The integrated construction also cuts installation times and avoids the need for adjustments.

The measuring system is available for Rexroth ball and roller rail systems. It can handle accelerations up to 500m/s and speeds up to 5m/s (or 10m/s, on request). A position resolution of up to 0.025m allows good control loop dynamics and thus short cycle times. The system accuracy of 4m/m is similar to that of glass scales, and allows repeatabilities of 0.25m.

Rexroth's inductive measurement system integrates with its linear guides, saving time, space and costs

Data from the system can be transmitted to drives or controllers via Hiperface or SSI/1Vpp interfaces. Drive-CLiQ and Fanuc versions are planned.

Several runner blocks can operate independently on one profile rail up to 4.5m long, without any accuracy limitations. The system components for example, rails and runner blocks can be replaced individually, if necessary, cutting servicing costs.

Additional temperature and motion sensors are built into the measuring system, making it ready for the requirements of Industry 4.0. For example, the extra sensors allow machine designers to read temperatures and actual dynamics. The data can also be used for predictive maintenance. If the built-in accelerometers detect changes such as increasing vibrations this may indicate wear or other problems. Maintenance can therefore be performed before a machine develops serious problems.