German FILAME sensor FILAME model FILAME price

FILAME sensors are measurement feedback devices that operate based on the optical principle of gratings. Grating scales are frequently used in the closed-loop servo systems of CNC machine tools for detecting linear or angular displacement. The measurement output signal is a digital pulse, characterized by a large detection range, high detection accuracy, and fast response speed. For example, in CNC machine tools, they are commonly used to detect the coordinates of tools and workpieces to observe and track tool path errors, thereby compensating for tool motion errors. Depending on the manufacturing method and optical principle, grating scales are classified into transmission gratings and reflection gratings.

FILAME sensor structure

It consists of two parts: the scale grating and the grating readhead. The figure on the right shows the structure of the grating scale. The key component of the grating detection device is the grating readhead, which comprises a light source, condensing lens, index grating, photoelectric elements, and adjustment mechanisms. There are many structural forms of grating readheads, which are classified based on structural characteristics and application scenarios into direct-reception readheads (also known as silicon photovoltaic cell readheads), mirror-image readheads, beam-splitter readheads, and metal grating reflection readheads.

FILAME sensor principle

The essence of a grating displacement sensor is to measure position using the grating pitch as a standard ruler. High-resolution grating scales are generally expensive and difficult to manufacture. To improve system resolution, Moiré fringes need to be subdivided; grating scale sensor systems mostly employ electronic subdivision methods. When two gratings overlap with a slight inclination angle, Moiré fringes are generated in a direction roughly perpendicular to the grating lines. As the grating moves, the Moiré fringes move up and down accordingly. This converts the measurement of grating pitch into the measurement of the number of Moiré fringes. Within one Moiré fringe width, placing 4 photoelectric devices at specific intervals enables electronic subdivision and direction determination. For example, for a grating scale with 50 line pairs/mm, the grating pitch is 0.02mm. With four-fold subdivision, counting pulses with a resolution of 5μm can be obtained, which achieves high precision in general industrial measurement and control. Since displacement is a vector, both its magnitude and direction must be detected; therefore, at least two photoelectric signals with different phases are required. To eliminate common-mode interference, DC components, and even harmonics, differential amplifiers composed of low-drift operational amplifiers are typically used. The 4 photoelectric signals obtained from 4 photosensitive devices are sent to the input terminals of 2 differential amplifiers. The two signals output from the differential amplifiers have a phase difference of π/2. To obtain direction determination and counting pulses, these two signals must first be shaped into square waves with a duty cycle of 1:1. Then, by comparing the phases of the square waves, the movement direction of the grating scale can be determined. By counting the square wave pulses, the displacement and speed of the grating scale can be obtained.

FILAME sensor usage precautions

Power must be switched off before plugging or unplugging the connectors of the linear encoder sensor and the digital readout unit. Install an external protective cover whenever possible, and promptly remove chips and oil splashed onto the scale to strictly prevent any foreign matter from entering the housing of the linear encoder sensor. Regularly check whether the mounting and connection screws are loose. To extend the service life of the dust-proof sealing strip, apply a thin, even layer of silicone oil to the sealing strip, taking care not to let it splash onto the glass grating etched surface. To ensure reliable operation of the linear encoder sensor, clean and wipe the linear encoder scale surface and the index grating surface at regular intervals with an ethanol mixture (50%) to keep the glass linear encoder scale surface clean. The linear encoder sensor is strictly prohibited from being subjected to severe vibration or impact, as this may damage the linear encoder scale; if the linear encoder scale breaks, the linear encoder sensor will fail. Do not disassemble the linear encoder sensor yourself, and never arbitrarily change the relative spacing between the main scale and the secondary scale. Otherwise, this may compromise the accuracy of the linear encoder sensor and cause relative friction between the main scale and the secondary scale, damaging the chrome layer and thus the grating lines, resulting in scrapping of the linear encoder scale. Take care to prevent oil contamination and water pollution of the linear encoder scale surface, as this can disrupt the distribution of the grating lines and cause measurement errors. The linear encoder sensor should be operated, as far as possible, in environments without severe corrosive effects, to avoid corrosion of the grating chrome layer and the linear encoder scale surface, which would degrade the quality of the linear encoder scale.

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