For linear displacement feedback, you can use a grating ruler or an electronic ruler. Is it better to use a grating ruler or an electronic ruler? What is the difference between the two? Below, I tell you.
1.
1. Working principle
Grating scale: The working principle of the grating displacement sensor is that the main grating* in a pair of grating pairs **That is, the ruler grating*** and the auxiliary grating***, that is, when the indicator grating*** undergoes relative displacement, under the simultaneous action of light interference and diffraction***, black and white or light and dark patterns are produced*** Regular striped patterns are called moiré fringes. After the optoelectronic device conversion, the black and white or light and dark stripes are converted into electrical signals with sinusoidal changes, which are then amplified by the amplifier and shaped by the shaping circuit to obtain two sine waves or square waves with a difference of 90o, which are sent to Enter the counting display of the grating digital display meter
Electronic ruler: Use the linear change of the resistance value to achieve the measurement purpose.
2. Output mode
Grating ruler: square wave *** three channels A, B, Z; six channels ***; sine; the back end must be equipped with a display meter or PLC < /p>
Electronic ruler: 0~10V, 4~20mA, 0~5V
3. Working voltage
Grating ruler: ±5V
Electronic ruler: maximum voltage 60V
4. Working temperature
Grating ruler:
-10 ~ +45℃
Electronic ruler: -60~150℃
5. Linearity
Grating ruler: measurement accuracy: ±6?m/m～
±10?m/m
Electronic ruler:
±0.01% or ±
0.05%
6. Response frequency
Grating Ruler: Execution speed: 100M/Min
Electronic ruler: Displacement rate: 4m/S~10m/S PKH
7. Repeatability
Grating ruler: 0mm
Electronic ruler: 0.01mm
2. Electronic ruler
Electronic ruler*** is also called linear displacement sensor and resistance ruler***. It is suitable for injection molding machines, woodworking machinery, printing presses, spray painting, machine tools, robots, engineering monitoring computer-controlled motion equipment, etc. where accurate displacement measurement is required.
Conductive plastic potentiometers, voltage dividers, and electronic scales were introduced in the late 1950s and are widely used in automobiles, injection molding machines, wood processing machines, and various modern industries. Relatively cheap sensors, low temperature changes, low-torque operation and high-speed applications are unique features of conductive plastic technology. The service life of the conductive plastic resistance scale MINOR*** can reach hundreds of millions of times, which can meet the needs of most high-speed industrial devices and is the mainstream development direction in the future.
3. Grating ruler
The grating ruler displacement sensor***referred to as the grating ruler*** is a measurement feedback device that uses the optical principle of the grating. Grating scale displacement sensors are often used in closed-loop servo systems of CNC machine tools and can be used to detect linear displacement or angular displacement. The measurement output signal is a digital pulse, which has the characteristics of large detection range, high detection accuracy and fast response speed. For example, in CNC machine tools, it is often used to detect the coordinates of the tool and the workpiece to observe and track the tool movement error, so as to compensate for the motion error of the tool.
Grating scale displacement sensors are divided into transmission gratings and reflection gratings according to different manufacturing methods and optical principles.
4. Principle of electronic ruler
The function of the motion sensor is to convert a mechanical displacement into an electrical signal, and the signal can be proportional to the mechanical movement. The brush assembly is wired to a mechanical actuator, which in turn creates a voltage divider across a plastic resistor rail. The resistor rails of the potentiometer ***1,3 *** are wired to a stable input DC voltage *** allowing small currents ***. When measured between the brushes and the modified resistor rail, the signal voltage is the dominant part of the voltage divider and is proportional to the brush position on the resistor rail. As a voltage divider, the potentiometer does not need to focus on the accuracy of the total resistance on the resistance rail, because temperature fluctuations only affect the resistance and will not affect the measurement results.
5. Principle of grating ruler
Take transmission grating as an example. When the lines on the indicator grating and the lines on the scale grating form a small angle θ, and the two When the grating ruler facets are placed relatively parallel, they are located on almost vertical grating lines under the illumination of a light source, forming alternating light and dark stripes. This type of fringe is called "Moiré fringe" ***shown on the right***. Strictly speaking, the direction of the moiré fringe arrangement is perpendicular to the bisector of the angle between the two grating lines. The distance between two bright lines or two dark lines in the moiré fringe is called the width of the moiré fringe, represented by W.
W=ω /2* sin***θ/2***=ω /θ .
I recommend: Precautions when using the grating ruler
***1*** When plugging and unplugging the grating ruler displacement sensor and the digital display meter plug socket, the power should be turned off.
***2*** Install a protective cover as much as possible, and promptly clean up chips and oil splashed on the ruler to strictly prevent any foreign matter from entering the grating ruler sensor housing.
***3*** Regularly check whether the installation connection screws are loose.
***4*** In order to extend the life of the dust-proof sealing strip, apply a thin layer of silicone oil evenly on the sealing strip, and be careful not to splash it on the scored surface of the glass grating.
***5*** In order to ensure the reliability of the grating scale displacement sensor, you can clean and wipe the grating scale surface with ethanol mixture ***50% each*** at regular intervals. and the indicating grating surface, and keep the glass grating surface clean.
***6*** The grating scale displacement sensor is strictly prohibited from being violently shaken or beaten to avoid damaging the grating scale. If the grating scale is broken, the grating scale sensor will be ineffective.
***7*** Do not disassemble the grating scale displacement sensor by yourself, let alone change the relative distance between the main scale and the auxiliary scale arbitrarily, otherwise the grating scale sensor may be damaged on the one hand. On the other hand, it may cause relative friction between the main scale and the auxiliary scale, damage the chromium layer and damage the grid lines, thus causing the grating scale to be scrapped.
***8*** Care should be taken to prevent oil and water from contaminating the surface of the grating scale, so as not to damage the stripe distribution of the grating scale and cause measurement errors.
***9*** The grating scale displacement sensor should try to avoid working in an environment with severe corrosion, so as not to corrode the grating chromium layer and the grating scale surface, and damage the quality of the grating scale.