What Is the Working Principle of Laser Displacement Sensor?

Laser displacement sensor is a sensor that uses laser technology to measure.

It consists of laser, laser detector and measuring circuit.

Laser sensor is a new measuring instrument.

It can accurately non-contact measure the position, displacement and other changes of the measured object.

It can measure displacement, thickness, vibration, distance, diameter and other precise geometric measurements.

Laser has excellent characteristics of good straightness.

Similarly, laser displacement sensor has higher accuracy than the known ultrasonic sensor.

However, the laser generating device is relatively complex and large, so the application range of laser displacement sensor will be demanding.

1. Basic principles

Laser displacement sensor can accurately non-contact measure the position, displacement and other changes of the measured object.

It is mainly used to detect the displacement, thickness, vibration, distance, diameter and other geometric quantities of the object.

According to the measurement principle, the principle of laser displacement sensor is divided into laser triangulation method and laser echo analysis method.

Laser triangulation method is generally suitable for high-precision and short-distance measurement, while laser echo analysis method is used for long-distance measurement.

The following two measurement methods of laser displacement sensor principle are introduced respectively.

At the position of the receiving element, the beam is processed by analog and electronic digital processing.

After internal micro processing and analysis, the corresponding output value is calculated, and then the output value is adjusted to emit a light to the object.

At this time, the beam of light can adjust the displacement distance.

Laser Displacement Sensor

2. Purpose

1. Length measurement

Place the measured component on the conveyor belt at the specified position.

The laser sensor detects the component and measures it at the same time with the triggered laser scanner, and finally get the length of the component.

2. Uniformity Inspection

Put several laser sensors in the tilt direction of the workpiece movement to be measured, and directly output the measurement value through one sensor.

In addition, a software can also be used to calculate the measurement value and read out the result according to the signal or data.

3. Inspection of electronic components

Use two laser scanners to place the measured components between them, and finally read out the data through the sensor, so as to detect the accuracy and integrity of the component size.

3. Triangulation

The laser transmitter shoots the visible red laser onto the surface of the measured object through the lens, and the laser scattered by the surface of the object passes through the receiver lens and is received by the internal CCD linear camera.

According to different distances, the CCD linear camera can “see” this light spot at different angles.

According to this angle and the known distance between the laser and the camera, the digital signal processor can calculate the distance between the sensor and the measured object.

At the same time, the position of the beam in the receiving element is processed by analog and digital circuits, and the corresponding output value is calculated through microprocessor analysis, and the standard data signal is output in proportion in the analog window set by the user.

If switching value output is used, it will be turned on in the set window and cut off outside the window.

In addition, the detection window can be set independently for analog and switching output.

The maximum linearity of the laser displacement sensor using triangulation method can reach 1um, and the resolution can reach the level of 0.1um.

For example, ZLDS100 type sensor can achieve 0.01% high resolution, 0.1% high linearity, 9.4KHz high response, and adapt to harsh environments.

4. Echo analysis

The laser displacement sensor uses the echo analysis principle to measure the distance to achieve a certain degree of accuracy.

The interior of the sensor is composed of processor unit, echo processing unit, laser transmitter, laser receiver and other parts.

The laser displacement sensor sends onemillion laser pulses to the detected object every second through the laser transmitter and returns to the receiver.

The processor calculates the time required for the laser pulse to encounter the detected object and return to the receiver, so as to calculate the distance value.

The output value is the average output of thousands of measurement results.

It is measured by the so-called pulse time method. Laser echo analysis method is suitable for long-distance detection, but the measurement accuracy is lower than laser triangulation method, and the farthest detection distance can reach 250m.

5. Measurement application

Laser displacement sensors are often used to measure physical quantities such as length, distance, vibration, speed, orientation, etc.

They can also be used for flaw detection and monitoring of air pollutants.

1. Size measurement:

Position recognition of micro parts;

Monitoring whether there are parts on the conveyor belt;

Detection of material overlap and coverage;

Control of manipulator position (tool center position);

Device status detection;

Detection of device position (through small holes);

Liquid level monitoring;

Thickness measurement;

Vibration analysis;

Collision test measurement;

Automobile related tests, etc.

2. Thickness measurement of metal sheet and sheet:

Laser sensor measures the thickness of metal sheet (sheet).

Thickness change detection can help find wrinkles, small holes or overlaps to avoid machine failure.

3. Measure the cylinder barrel and measure at the same time:

Angle, length, inner and outer diameter eccentricity, conicity, concentricity and surface profile.

4. Length measurement:

Place the measured component on the conveyor belt at the specified position, the laser sensor detects the component and measures it at the same time with the triggered laser scanner, and finally get the length of the component.

5. Uniformity Inspection:

Put several laser sensors in the tilt direction of the workpiece movement to be measured, and directly output the measurement value through one sensor.

In addition, a software can also be used to calculate the measurement value and read out the result according to the signal or data.

6. Inspection of electronic components:

Use two laser scanners to place the measured components between them, and finally read out the data through the sensor, so as to detect the accuracy and integrity of the component size.

7. Inspection of filling level on the production line:

Laser sensor is integrated into the production of filling products.

When the filling products pass through the sensor, it can detect whether they are full.

The sensor can accurately identify whether the filling of filling products is qualified and the quantity of products by using the extended program of laser beam reflection surface.

8. Straightness of the object measured by the sensor:

First, you need 2-3 laser displacement sensors for combined measurement, as shown in the figure.

Then install the three laser displacement sensors on a straight line parallel to the production line, and determine the spacing between the three laser displacement sensors according to the measurement accuracy you need.

Finally, you need to make this object move in a direction parallel to the installation line of the laser displacement sensor.

When the production line is parallel to the installation line of the sensor, the greater the distance difference measured by the three sensors, the worse the straightness of the object.

The smaller the distance difference measured by the three sensors, indicating that the straightness of the object is better.

You can establish a percentage of straightness according to the length of the object you want to measure and the spacing between the installation of the three sensors, so as to obtain a quantitative signal output.

The purpose of detecting the straightness of objects has been achieved.

6. Displacement sensor classification

1. Eddy current displacement sensor

Resolving power:

The highest resolution of the eddy current sensor can also reach 0.1M, which is basically equivalent to the laser displacement sensor.

Linearity:

The linearity of eddy current sensor is generally low, about 1% of the range, and that of high-end laser displacement sensor is generally 0.1%.

Measurement conditions:

Eddy current sensors require the tested body to be a conductor and non-magnetic, that is, a non-magnetic conductor, such as aluminum, copper, etc., but not iron;

The laser displacement sensor can measure whether the measured object is magnetic or conductive.

2. Capacitive displacement sensor

The precision of capacitive displacement sensor is very high, which is much higher than that of laser displacement sensor, but the range of capacitive displacement sensor is very small, generally less than 1mm, and the maximum range of laser displacement sensor can be 2m.

3. Optical fiber displacement sensor

The measurement principle of the optical fiber displacement sensor is to measure the displacement of the object by measuring the change of the luminous flux and light intensity reflected from the surface of the object due to displacement.

Its probe is composed of transmitting optical fiber and receiving optical fiber.

For the displacement and vibration of a small object, the conventional non-contact displacement sensor receives the limitation of the reflection area, which leads to the unsatisfactory measurement effect, while the optical fiber displacement sensor can be made into a very small probe (with a minimum diameter of 0.2mm).

In addition, it can also be made into the form of linear transmission and reception.

The displacement value can be calculated by measuring the shielding degree of the object to the optical fiber during the displacement process, and the accuracy can reach 0.01um.

The maximum measuring range is 4mm.

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