How Gratings Work On CNC Machine Tools


A grating is an optical element that works by utilizing the transmission and diffraction phenomena of light. The grating detection device is widely used, its measurement accuracy can reach plus or minus μm, and has the advantages of high precision, fast response speed, and wide range. There are linear gratings and circular gratings, which are used to measure linear displacement and angular displacement respectively.
 

1. Structure of the grating detection device

 
The structure of the grating device is composed of a scale grating and an indicator grating. There are many of the same density on the scale grating and the indicator grating, which are called grating fringes. For transmission gratings, this line is not I (for reflection gratings, this line does not reflect light), the light is transmitted (or reflected back) by the narrow surface between the two lines.
 

2. The working principle of the grating measuring device

 
Place the indicator grating parallel to the side of the ruler grating, and make their lines relatively inclined by a small angle θ, and place the light on the other side of the ruler grating (take the directional mimeograph as an example). When light passes through them, Nir fringes, which are streaks of light and dark, are created on mimeographs. When the mimeograph is instructed to move, the Nir fringes move, and the moving direction is almost perpendicular to the grating moving direction. The relationship between Moire fringe spacing and line spacing W≈P/θ In the formula, W is the Moiré fringe spacing; P is the distance between two scribed lines; θ is the relative inclination angle (rad) between the two feet.
 
Moyun fringe has a magnifying effect. If P=0.01mm, θ=0.001, then W=10mm, which is equivalent to magnifying the distance between the two-foot engraved lines by 1000 digits. The photoelectric element moves with the instructing mimeograph. When moving, the light received by the photoelectric element is affected by the Moire fringe and changes in a sinusoidal pattern, so the photoelectric element generates a current (voltage 0) that changes according to the sinusoidal law. The displacement of the moving part can be measured by analyzing the change law of the current or voltage. , speed and direction of movement.
 
The structure of the DC servo motor mainly includes three parts.
 
Stator: The magnetic field is generated by the poles of the magnet. According to the way of generating the magnetic field, DC servo motors can be divided into permanent magnet type and separately excited type. The permanent magnetic pole is made of permanent magnet material. The separately excited magnetic pole is made of stamped silicon steel sheets and stacked, and the coil is wound outside, and a DC current is passed to generate a constant magnetic field.
 
Rotor: The rotor is made of silicon steel, with coils embedded on the surface. When DC current is applied, an electromagnetic torque is generated to drive the load to rotate under the action of the stator magnetic field.
 
Brushes and commutator segments: In order to keep the generated electromagnetic torque in a constant direction, the rotor can rotate evenly and continuously in a given direction, the brushes are connected to the external DC power supply, and the commutator segments are connected to the armature conductors.
 
Considering the actual operation, the DC servo motor introduces a mechanical commutation device. The three highs]have many failures and difficult maintenance, often affect production due to sparks generated by carbon brushes, and cause electromagnetic interference to other equipment. At the same time, the commutation capability of the mechanical arrester limits the capacity and speed of the motor. The armature of the motor is on the rotor, which makes the motor inefficient and poor in heat dissipation. In order to change the commutation ability and reduce the leakage inductance of the armature, it is short and thick, which affects the dynamic performance of the system.

 


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