German BALLUFF sensors, BALLUFF models, BALLUFF prices

BALLUFF sensors are devices that convert magnetic signals into electrical signals. By utilizing the transformation relationship between magnetic quantities and other physical quantities, with the magnetic field as a medium, they can also convert signals of other non-electrical physical quantities into electrical signals. There are two driving methods: one is driven by a permanent magnet, and the other is driven by an electromagnetic coil. The former is mostly used for detection; for example, if a moving part is made of a magnet, it will attract and emit a signal once it approaches the magnetic induction sensor. The latter is mostly used for control; if the electromagnetic coil is energized, the contacts will attract. Using magnetic induction sensors to replace limit switches that rely on collision contact can improve system reliability and service life; therefore, they are often used in programmable logic controllers (PLCs) as signaling devices for position arrival.

BALLUFF sensor structure

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

BALLUFF sensor principle

The essence of a grating displacement sensor is to measure position using the grating pitch as a standard ruler. High-resolution linear encoder scales are generally expensive and difficult to manufacture. To improve system resolution, Moiré fringes need to be subdivided; grating scale sensor systems mostly use 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 the grating pitch into the measurement of the number of Moiré fringes. Within the width of one Moiré fringe, placing 4 photoelectric devices at certain intervals enables electronic subdivision and direction judgment functions. For example, for a grating scale with 50 line pairs/mm, the grating pitch is 0.02mm. If four-fold subdivision is adopted, 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, so at least two photoelectric signals with different phases are required. To eliminate common-mode interference, DC components, and even harmonics, a differential amplifier composed of low-drift operational amplifiers is usually used. The 4 photoelectric signals obtained from 4 photosensitive devices are sent to the input terminals of 2 differential amplifiers respectively. The two signals output from the differential amplifier have a phase difference of π/2. To obtain direction judgment and counting pulses, these two signals need to be shaped, first into square waves with a duty cycle of 1:1. Then, by comparing the phase 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.

BALLUFF sensor usage precautions

Power off before plugging or unplugging the connector between the linear encoder sensor and the digital readout. Install an external protective cover whenever possible, promptly remove chips and oil splashed onto the scale, and strictly prevent any foreign matter from entering the linear encoder sensor housing. 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 splash it onto the glass grating etched surface. To ensure reliable operation of the linear encoder sensor, periodically clean and wipe the linear scale surface and the index grating surface with an ethanol mixture (50%) to keep the glass linear scale surface clean. The linear encoder sensor must not be subjected to severe vibration or impact, as this may damage the linear scale; if the linear 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, as 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 scale. Take care to prevent oil contamination and water from polluting the linear scale surface, which could disrupt the distribution of the grating lines and cause measurement errors. Avoid operating the linear encoder sensor in environments with severe corrosive effects, to prevent corrosion of the grating chrome layer and the linear scale surface, which would degrade the quality of the linear scale.

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