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What is Magnescale?

Mounting allowance

Magnescale is constructed so that the sensor for signal detection slides along the guide in the scale with bearings to detect the position. Therefore, it can perform stable, high-precision detection even in the presence of a positional deviation of the scale or head caused by installation or disagreement in parallelism with the machine guides.

Vibration and impact resistance

Magnescale primarily uses ferrous members as the housing material to protect the detector section, thereby realizing the high vibration resistance and impact resistance characteristics. In the SR80 series, furthermore, it employs multi-point fixation construction in addition to the housing with high rigidity, achieving the industry's top class vibration resistance and impact resistance.

Thermal characteristics

Magnescale have the same linear expansion coefficient as that of cast iron used for the structure of general machine tools. Therefore, it exhibits the same behavior as the equipment in which it is installed even in environments where temperature changes, making very stable control possible. In particular, the SR80 series scales can be installed in close contact with the equipment; heat exchange with the equipment is effectively achieved, enabling them to attain consistent accuracy even in an environment in which temperature changes occur.

Resistant to condensation and oil

Magnescale employs the magnetic detection principle, thus far less affected by the condensation or oil problems inherent in machine tools and making stable and high precision operation possible in severe environments.

Scale construction

The magnetic signal detection sensor is supported by a bearing, maintaining a non-contact status with respect to the scale material. This bearing runs on the guide incorporated in the scale and detects the equipment's traveling distance. Therefore, the sensor has very small sliding resistance, enabling the scale to be used even for equipment with small driving force. Moreover, the use of a specially constructed sealing structure helps to prevent dust and dirt from entering inside the scale. In addition, air purging the scale provides further protection.

Measurement Principle

Scale material

The magnetic recording media, or the raw material for scales, was developed as the scale material that realizes high-density recording at high precision, based on Magnescale's magnetic technology that has been cultivated for magnetic tapes and magnetic discs. The scales adopt magnetic metal powder that is used for data storage systems because of its high density and reliability. Its magnetic characteristics are that Br: 0.2 to 0.25T and Hc: approximately 120 kA/m. The magnetic media form a strong coated surface resistant to cutting fluids and strong alkaline solutions through a hardening process after coating.

  • Magnetic media's B - H curve

Signal detection sensor(MR sensor)

The MR sensor is a thin-film sensor patterned on a PWB. It obtains the signal output through the change in the resistance value according to the size of magnetic field leakage from the scale when it moves keeping a certain distance from the magnetic media (scale) to which magnetic signals have been recorded as shown in Figure 1. In this case, however, the signal obtained from the resistance change characteristics of the sensor and the status of magnetic field leakage from the scale also contains distortion components (such as harmonic components) in addition to the sine wave components of the signal pitch. Therefore, the sensor is positioned by shifting it in the operating direction by the distance of 1/6 of another signal pitch λ (Figure 2). In this case, when third-order harmonic components are observed, the following Equation "A" is established for three-fold periodic signal components because 1/6 of the signal pitch λ is π/3 in the periodic phase, and the phase is shifted by 180° with respect to the three-fold periodic signal components of the first sensor, resulting in a reverse signal. The addition of this signal enables the third-order harmonic components to be cancelled out. That is, the combination of these sensors enables harmonic components of the 3n-th orders to be canceled out. In the same way, the combination of multiple units of the sensors also enables the harmonic components of other orders such as 5th and 7th orders to be cancelled out simultaneously. In detection sensors, the circuit is generally formed in a bridge structure for stability of the temperature characteristics, etc. as well. In that case, distortion of odd numbered orders are cancelled out by the arrangement of sensors configuring a bridge. Therefore, the use of the bridge structure and the arrangement of the sensor configuration that cancels out harmonic components of the extent of the 3rd, 5th, and 7th orders enable a signal close to sine waves to be obtained. In this way, the scale achieves high precision and high resolution by digitization of electrical interpolation based on a distortion-less signal, coinciding with various electrical signal compensation.

  • Equation A
  • Figure 1: Arrangement of MR element and magnetic media
  • Figure 2: Structure of high-precision Magnescale