The essence of measuring the displacement of the magnetic grid is to measure the position of the magnetic grid with a standard ruler. High-resolution magnetic scales are generally more expensive and difficult to manufacture. In order to improve the resolution of the system, it is necessary to subdivide the moiré fringe, and the magnetic scale sensor system mostly adopts the electronic subdivision method. When two magnetic grids overlap with a slight inclination angle, moiré fringes will be generated in a direction roughly perpendicular to the grating scribe line. As the magnetic grid moves, the moiré fringes will also move up and down. In this way, the measurement of the magnetic grating pitch is converted to the measurement of the number of moiré fringes.

Within the width of a Moiré fringe, placing 4 optoelectronic devices at intervals as needed can realize the electronic subdivision and orientation function. For example, a grating ruler with a grating line of 50 pairs/mm has a grating pitch of 0.02mm. If four subdivisions are used, a count pulse with a resolution of 5μm can be obtained, which has reached a very high level in general industrial measurement and control. Accuracy. Since the displacement is a vector, it is necessary to detect its magnitude and its direction, so at least two photoelectric signals with different phases are required. In order to eliminate common-mode interference, DC components and even harmonics, a differential amplifier composed of a low-drift operational amplifier is usually used.

The 4 photoelectric signals obtained by 4 photosensitive devices are respectively sent to the input terminals of 2 differential amplifiers. The phase difference of the two signals output from the differential amplifier is π/2. In order to obtain the direction and count pulses, it is necessary to correct The two signals are reshaped, and they are first reshaped into a square wave with a duty ratio of 1:1. Then, by comparing the phase of the square wave, you can wait until the moving direction of the magnetic scale. By counting the square wave pulses, the displacement and speed of the grating ruler can be obtained.