A laser displacement sensor is a measuring instrument that uses laser technology to measure the position, displacement and other changes of a measured object. It consists of a laser, a laser detector and a measuring circuit.
This type of sensor offers accurate non-contact measurements and is capable of measuring displacement, thickness, vibration, distance, diameter and other precise geometric measurements. The laser used in the sensor has excellent straightness characteristics.
Compared to ultrasonic sensors, laser displacement sensors have a higher level of accuracy. However, the laser generating device is relatively complex and large, limiting the range of applications for laser displacement sensors.
1. Basic principles
A laser displacement sensor is a device that accurately measures the position, displacement, and other changes of an object without physical contact. It is widely used to detect displacement, thickness, vibration, distance, diameter and other geometric properties of objects.
The principle of a laser displacement sensor is divided into two methods: laser triangulation and laser echo analysis. The laser triangulation method is typically used for high-precision, short-distance measurements, while the laser echo analysis method is suitable for long-distance measurements.
The following is a brief introduction to these two measuring methods of laser displacement sensor principle.
The beam is processed by analog and digital electronic processing at the position of the receiving element. After microprocessing and internal analysis, the corresponding output value is calculated, and the output value is used to adjust the light emission to the object. This adjusts the travel distance of the light beam.
2. Objective
1. Length measurement
To measure a component, place it in the designated position on the conveyor belt. The laser sensor, driven by the laser scanner, will detect and measure the component, ultimately determining its length.
2. Uniformity inspection
Place several laser sensors in the tilt direction of the part to be measured and have one sensor directly output the measurement value. Additionally, software can be used to calculate the measurement value and display the result based on the received signal or data.
3. Inspection of electronic components
Use two laser scanners to position the components being measured between them, then obtain data through the sensors to assess the accuracy and completeness of the component dimensions.
3. Triangulation
The laser transmitter projects a visible red laser onto the surface of the object being measured through a lens. The laser light scattered from the surface of the object then passes through the receiver lens and is detected by the internal CCD linear camera.
Based on the distance from the object, the CCD linear camera detects the light spot at different angles. Using this angle and the known distance between the laser and the camera, the digital signal processor calculates the distance between the sensor and the object.
The position of the beam on the receiving element is then processed by analog and digital circuits, and the corresponding output value is calculated by the microprocessor. The standard data signal is output proportionally in the user-defined analog window. If the switching value output is selected, it will be activated within the defined window and turned off outside of it.
Both analog and switching outputs can have separate detection windows. The laser displacement sensor, using triangulation, can achieve maximum linearity of 1um with 0.1um resolution. For example, the ZLDS100 type sensor has a high resolution of 0.01%, a high linearity of 0.1%, a fast response of 9.4 KHz, and the ability to perform in harsh environments.
4. Echo Analysis
The laser displacement sensor uses the principle of echo analysis to measure distance accurately. The sensor consists of a processor unit, echo processing unit, laser transmitter, laser receiver and other components.
Every second, the laser transmitter sends a million laser pulses to the object being detected, which then returns to the receiver. The processor calculates the time it takes for the laser pulse to reach the object and return, allowing the distance value to be calculated.
This value is determined by taking the average of thousands of measurements using the pulse time method. Although the laser echo analysis method is suitable for long-distance detection, it has lower accuracy compared with the laser triangulation method. The longest detection distance it can achieve is 250 meters.
5. Measurement application
Laser displacement sensors are widely used to measure various physical quantities, including length, distance, vibration, speed, orientation and more. These sensors have also found applications in fault detection and monitoring of air pollutants.
1. Size measurement:
- Recognition of the position of microcomponents
- Detection of the presence of components on the conveyor belt
- Overlap detection and material coverage
- Manipulator position control (center point of the tool)
- Device status monitoring
- Device position detection using small openings
- Monitoring liquid levels
- Thickness measurement
- Vibration analysis
- Crash Test Measurement
- Automobile related tests, etc.
2. Thickness measurement of metal sheets and sheets:
A laser sensor is used to measure the thickness of metal sheets.
Detecting changes in thickness can help identify wrinkles, small holes or overlaps, thus preventing machine failures.
3. Measure the cylinder and measure at the same time:
- Angle
- Length
- Eccentricity of inner and outer diameter
- Taper
- Concentricity
- Surface profile.
4. Length measurement:
Place the component to be measured in the designated position on the conveyor belt. The laser sensor will then detect the component and simultaneously measure it using the driven laser scanner, ultimately determining its length.
5. Uniformity inspection:
Arrange several laser sensors in the direction of inclination of the part to be measured. The measurement value can be output directly via one of the sensors. Furthermore, a software program can be used to calculate the measurement value based on the signals or data and provide the result.
6. Inspection of electronic components:
Place the measured components between two laser scanners and then read the data through the sensor to detect the accuracy and completeness of the component size.
7. Filling level inspection in production line:
The laser sensor is integrated into the product filling production process. As filling products pass the sensor, it can accurately detect whether they are filled to maximum capacity. The sensor uses an advanced laser beam reflection program on the surface to accurately determine whether the filling of the products is in accordance with the standard and quantity of the products.
8. Straightness of the object measured by the sensor:
First, you will need 2 to 3 laser displacement sensors for a combined measurement, as illustrated in the figure.
Then, place the three laser displacement sensors in a straight line, parallel to the production line, and determine the spacing between them based on the desired measurement accuracy.
Finally, make the object move in a direction parallel to the installation line of the laser displacement sensors.
When the production line is aligned with the sensor installation line, the greater the distance difference measured by the three sensors, the worse the straightness of the object. On the other hand, a smaller difference in the distance measured by the three sensors indicates that the object is straighter.
You can calculate the percentage of straightness by taking into account the length of the object to be measured and the spacing between the three sensor installations, resulting in a quantifiable output signal.
With this configuration, you have successfully achieved the goal of detecting the straightness of objects.
6. Displacement sensor classification
1. Eddy current displacement sensor
Resolving power:
The resolution of an eddy current sensor can reach 0.1 mm, which is comparable to that of a laser displacement sensor.
Linearity:
The linearity of an eddy current sensor is normally low, around 1% of the measuring range. On the other hand, state-of-the-art laser displacement sensors have a linearity of about 0.1%.
Measurement conditions:
Eddy current sensors require the test object to be a conductive, non-magnetic material such as aluminum or copper, but not iron.
Laser displacement sensors, on the other hand, are capable of measuring magnetic and conductive objects.
2. Capacitive displacement sensor
The accuracy of capacitive displacement sensors is incredibly high, surpassing that of laser displacement sensors. However, its range is quite limited, generally less than 1 mm. On the other hand, laser displacement sensors have a much wider range, with a maximum measurement range of up to 2 meters.
3. Optical fiber displacement sensor
The measuring principle of a fiber optic displacement sensor is to determine the displacement of an object by detecting changes in the luminous flux and the intensity of light reflected from the surface of the object due to the displacement.
The sensor probe consists of a transmitting optical fiber and a receiving optical fiber.
For small objects, conventional non-contact displacement sensors are limited by the reflection area, resulting in poor measurement performance. However, the fiber optic displacement sensor can be designed with a very small probe (minimum diameter of 0.2 mm), making it suitable for measuring small objects.
Furthermore, it can be done in the form of linear transmission and reception.
The displacement value is calculated by measuring the degree of shielding of the object to the optical fiber during the displacement process, with an accuracy of up to 0.01um.
The maximum measuring range of the sensor is 4 mm.
