Heavy duty absolute encoder offers improvements in safety and performance

The LinACE system has an accuracy of ±5µm and is optimised so that users can achieve full closed-loop control, improving safety and performance. The encoder comprises a solid steel shaft with fully integrated scale and a sliding readhead module that has no internal moving parts, making it resistant to shock and vibration. As with most actuators, the shaft is made from steel to exploit its 'soft' magnetic characteristics. The absolute code under the shaft surface is composed of small circumferential grooves, which are filled with a non-magnetic material such as hard chrome or copper, depending on the application. The surface is plated with hard chrome. Because the scale is passive, Renishaw claims external magnetic fields have negligible effect and LinACE is completely immune to dirt contamination. Furthermore, the scale manufacturing technique retains a hard, smooth outside surface on the shaft, so operation of the actuator is not affected by its presence. Shaft diameters range from 4 to 30mm and measuring lengths are up to 750mm. The module includes two bronze bearings that are integrated into the stainless steel housing to allow smooth movement, whilst at the same time maintaining precise alignment of the sensor over the shaft, even under hostile conditions. Placing the scale directly on the actuator shaft is said to provide several metrology benefits. Firstly, the system has an accuracy of ±5 µm, thanks to internal compensation inside the readhead. Secondly, because the scale is marked directly onto the actuator shaft, it gives direct measurement of the actual position of the shaft, eliminating hysteresis and backlash while improving repeatability and stability. According to Renishaw, the LinACE system can be fitted directly onto the front of the actuator, minimising overall system size, reducing complexity and eliminating potential failure modes by removing the need for parallel measuring systems.