Electromagnetic encoders, based on a static transmission line working at microwave circuits and a movable chain of metallic or dielectric inclusions, constitute a good alternative to the well-known optical encoders. Optic systems present very good spatial resolution, but they exhibit a limited robustness for operation under harsh/hostile conditions, or in environments subjected to pollution or dirtiness, such as those encountered in many industrial scenarios. Magnetic encoders and Hall-effect sensors are also of interest for motion control, but such sensors are based on inductive elements or magnets, thereby representing a higher cost solution, as compared to electromagnetic encoders.
Additionally, electromagnetic encoders can be used as Chipless RadioFrequency IDentification (RFID) tags. Namely, a certain identification code can be provided to the chain of inclusions. Near-field Chipless-RFID systems are of interest in Smart Packaging and logistics applications.
Technology description and motivation
Electromagnetic encoders can be considered to be the microwave counterparts of optical encoders, and indeed the working principle is very similar. In electromagnetic encoders, a microwave signal, rather than an optical beam, is used for detecting the motion of the movable part. Such microwave signal feeds a transmission line, eventually loaded with a resonant element, or various resonant elements, which acts as the static part of the encoder. The movable part consists of a dielectric slab (circular in rotary encoders) with a chain, or multiple chains, of inclusions (either metallic, dielectric, or, even, apertures). The functionality is also based on pulse counting, based on the amplitude modulation (AM) signal generated by the inclusions, in relative motion with regard to the reader (static part). As compared to optical encoders, electromagnetic encoders cannot provide a resolution as good as that of optical encoders, but in many applications the achievable resolution is sufficient, and the use of electromagnetic encoders is justified by the lower cost and major robustness.
Additionally, electromagnetic encoders can be used as chipless-RFID tags. The working principle of the chipless-RFID tags subject of this project is identical to the one of the electromagnetic encoder systems devoted to the measurement of displacement and velocities. The chain of inclusions generate an AM signal, when it is displaced over the sensitive part of the reader, and the envelope function contains the ID code in the form of peaks or dips associated to the logic state ‘1’ or ‘0’ (depending on the specific configuration). The main general advantage of chipless-RFID over the chip-based counterparts is the lower cost, related to the absence of the chip, which is replaced with a metallic pattern, typically. The limitation is the need to read by proximity and proper alignment between the tag and the reader.
Main technical aspects
Applications
Further research required
Studies are being carried out in order to to boost up the number of bits per encoder position. Strategies based on combining time-division multiplexing scheme with frequency division, phase division, or both frequency/phase division multiplexing are being considered.
Partners for future research
Looking for companies or institutions for joint developement of the technology and detection of new applications, through R+D+i projects or contracts
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