This article presents a contactless measurement technique of the rotor temperature of small rotating machines using Near-Infrared Fiber Bragg Gratings (FBGs) sensors. This principle allows localizing heat spots in the rotor of electrical machines. The temperature information can be used to protect the machine by stopping its operation due to a heat spot. The concept is to measure the wavelength shift due to temperature changes for several FBGs integrated into a rotor. First, the temperature response of the FBG is simulated using Matlab. Then, a test bench is designed including a geometrically small electrical motor, a mechanical coupler, two bearings and a 3D printed cylinder. It has a rotational speed equivalent to a real electrical machine. The measurement principle uses a super-luminescent diode (815-855 nm) which is continuously coupled into an FBG embedded onto the rotor using suitable optics. The heating system is calibrated using a T-type thermocouple (class A: +/- 1 °C). Then, the Fiber Bragg Grating is heated while rotating the cylinder. The reflected signals are detected by a spectrometer. Finally, wavelength shifts due to temperature variations (10°C steps from 20 °C up to 70 °C) are experimentally measured up to 754 RPM. A temperature sensibility of 4.7 pm/°C is experimentally reached. As future work, the system with several gratings will be integrated into a small power rotating machine (kW) suitable for automotive applications. Reflected signals that correspond to temperature variations will be detected while rotating the FBGs to measure high temperatures ~ 150 °C for 1500 RPM.
This paper illustrates the energy harvesting principle established in an optical micro-electro-mechanical system (MEMS) using a vertical multi-junction photovoltaic cell (PV cell: 3*3*0.1 mm). The micro-system is a bistable micro-actuator which includes two active shape memory alloy elements (SMA: 3*1*0.1 mm), heated by a laser beam. The SMA elements are used as a biasing spring to activate the micro-system. In this study, the focus is only on actuating the SMA while harvesting energy converted from laser lighting. First, the laser is homogenized using an N-BK7 light pipe homogenizing rod (75*2 mm). Then, the uniformity is verified experimentally using an optoelectronic system able to measure the power on every 800 μm of the surface; resulting an average output power of 100 mW with a variation of ±9%. Next, the current/voltage (IV) curve of the PV cell is extracted, for an irradiance of 1.05 W/cm2, giving a maximum electric power of 32.5 mW. The set-up for the system is modelled using Creo software and executed by resin 3D printing. Finally, the actuation of each SMA element is done alternately (period = 6 sec) using a MEMS active mirror which steers the homogenized laser onto them. While cycling, the unused optical energy from the laser is detected by the PV cell resulting to harvest around 60 mJ per cycle. This energy is stored in a solid state thin film micro-battery. In the future work, the SMA elements will actuate the bistable micro-actuator and the quantity of energy harvested will be extracted.
This article presents an endoscopic 3D printer using the photo-polymerization additive method. The proposed endoscopic principle allows printing 3D objects through a flexible optical image guide. The concept is first to transmit a pattern using ultraviolet light projected through the endoscopic optical system on the printing surface. A layer by layer printing is performed by moving the focusing plane along the z-axis. The endoscopic optical design is based on a Digital Micro-Mirror (DMD) projector, an image guide (a fiber bundle of 70 000 fibers) and optical lenses. It is modeled and simulated using the Zemax optical software. The projected pattern from the DMD is injected into the image guide. Then, the pattern is refocused on the printing surface, which is the transparent bottom of a vat full of resin. First, optical losses and homogeneity of the endoscopic optical system are measured. Then, photopolymer parameters of used resin (Formlab RS-F2-GPWHH-04) are experimentally evaluated. Finally, different multi-layer objects (typically 30 layers) are printed to validate the concept of 3D endoscopic fabrication. Using a 405 nm LED, an optical irradiance of 1.7 mW/cm² on the printing surface is reached. 3D parts are printed with a lateral resolution of 150 μm and a layer thickness of 100 μm on a circular printing surface of 9.54 mm diameter.
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