NTN Develops Bearing w/ Rotation Sensor, 40 Times Higher Resolution
NTN Corp developed a bearing with a high-resolution rotation sensor in collaboration with SNR of France.
The new bearing features a rotation detection capability that is up to 40 times higher than that of the company's existing products. The bearing allows a higher definition and lower energy consumption when it is used in a color copier, rotation control device, etc.
The line sensor manufactured by SNR is provided with multiple magnetic sensors arranged on an IC. As with the existing products, the line sensor uses a ring magnet and the magnetic sensors. When the magnet rotates, the N and S poles alternately passes in front of the magnetic sensors. It is the measurement method that differs from the existing products.
In contrast to the existing method where one pulse is generated each time the N or S pole passes by, the new method allows the continuous measurement during the period between the two poles, thereby enabling the output of higher-resolution rotation signal.
The line sensor used in the new bearing has the operating principle that is equivalent to that employed by NTN's bearing released Aug 2007. The line sensor is provided with two groups of magnetic sensors aligned at an interval with half the distance of the pole pitch. The polarization is performed such that the magnetic intensity is indicated by a sine curve with respect to θ, where θ is the distance from the N pole.
Thus, the phases are displaced by 90° from each other so that the sine wave can be obtained by the first sensor group, and the cosine wave can be obtained by the second group. Based on the values of the sine and cosine waves, the line sensor can measure the position even between the poles.
The IC measures 6 x 7mm. With the adoption of NTN's proprietary technology to mount a sensor on a bearing, the new product provides a high resolution despite its small size.
As a starter, the company commercialized a ball bearing unit with an inner diameter of 15mm and outer diameter of 35mm, which outputs up to 1,280 pulses of 2-phase signal (phases A and B) per rotation. This corresponds to a rotational angle of approximately 0.3° per pulse. The product is also capable of detecting the rotational direction.
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