Laser Distance Sensors vs Laser Displacement Sensors: What's the Difference?
The Rise and Development Trends of Optical Measurement Sensors
In fields such as manufacturing, precision instruments, biomedicine, and aerospace, the demand for measurement accuracy and efficiency is steadily increasing. Non-contact, digital, high-precision, and highly sensitive optical measurement sensors, especially laser distance sensors and laser displacement sensors, are providing more precise, efficient, and intelligent measurement solutions across various industries.
The Fundamentals and Classification of Laser Distance Measurement Technology
Based on the fundamental principles of laser measurement, the methods can be divided into the Time of Flight (ToF) method and the triangulation method. Among them, the Time of Flight method can be further categorized into the Pulse Method (ToF) and the Phase-Shift Method.
As shown in the diagram below.
Pulse Method (ToF): The Ideal Choice for Long-Distance and Large-Scale Measurement
Principle:
The Pulse Method (ToF) is based on measuring the time it takes for a laser pulse to travel from the emitter to the target and back to the receiver. A laser pulse is emitted, reflects off the target, and the time difference between emission and reception is recorded. Using the speed of light 𝑐 and the time difference 𝑡, the distance 𝑑 to the target can be calculated using the formula:
where 𝑑 is the distance to the target, 𝑐 is the speed of light (3 ×10^8 m/s), and 𝑡 is the round-trip time. The division by 2 accounts for the round-trip nature of the measurement.
NOTE: The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).
The pulse method (ToF) is especially suitable for applications requiring the measurement of long distances or large areas, such as drone mapping, 3D map construction, environmental monitoring (e.g., the vertical distribution of pollutants in the atmosphere), and obstacle detection and avoidance in autonomous vehicles.
LiDAR (Laser Detection and Ranging): In fields such as autonomous driving, robotic navigation, terrain mapping, and 3D modeling of buildings, LiDAR systems utilize the pulse method (ToF) to obtain high-precision 3D spatial information, providing critical data support for decision-making.
Aerospace: The pulse method (ToF) is also used for precise distance measurement between spacecraft and the ground or target objects, ensuring the safe execution of missions such as lander navigation and Mars rover exploration.
Phase-Shift Method: Reliable Technology for Medium and Short-Distance High-Precision Measurement
Principle:
The Phase-Shift Method involves modulating the laser beam and measuring the phase difference between the emitted and received signals to calculate distance. The laser beam is modulated as a sinusoidal wave, and the phase shift Δ𝜙 between the transmitted and reflected waves is measured. This phase shift is directly related to the distance to the target, and the distance 𝑑 can be calculated using the formula:
where 𝑑 is the distance to the target, 𝑐 is the speed of light (3 ×10^8 m/s), Δ𝜙 is the phase shift, and 𝑓 is the modulation frequency.
The phase-shift method provides higher measurement accuracy than the pulse method (ToF) at medium and short distances, making it an indispensable tool in industrial automation. For example, phase-shift laser sensors play a crucial role in precise positioning of robotic arms, alignment of parts on automated assembly lines, and precision machining in CNC machines.
Quality inspection: In manufacturing, phase-shift laser sensors are used to measure surface flatness, thickness, and small dimensional changes in products, aiding in quality control and process monitoring.
Scientific research: In fields like physics and materials science, the phase-shift method is used to study the microscopic structure and properties of materials, such as measuring thin film thickness and analyzing surface roughness.
Triangulation Method: A Precision Tool for Ultra-Short-Distance Measurement
Principle:
The Triangulation Method is based on geometric triangulation, where the known positions of the laser emitter and receiver, along with the reflected laser beam, form a triangle. The laser beam is emitted towards the target and reflected back to the receiver. By measuring the angular difference 𝜃 between the emitted and reflected beams and using the known baseline distance 𝐿 between the emitter and receiver, the distance 𝑑 to the target can be calculated using the formula:
where 𝐿 is the known baseline distance between the emitter and receiver, and 𝜃 is the angle of the reflected beam.
Triangulation is a geometric measurement method based on triangular relationships. In this method, a laser spot is projected onto the object to be measured, and the reflected light from the object is directed at a certain angle towards the CMOS sensor element. The position of the light spot on the CMOS line changes according to the distance of the object. In this way, even at very small distances, the distance to the object can be precisely determined.
Ultra-short distance high-precision measurement: The triangulation method, known for its extremely high measurement accuracy and stability, is widely used in fields such as electronic component processing, semiconductor manufacturing, and precision machining. It can accurately measure small dimensional changes, such as line widths on chips and dimensional tolerances of components.
Automotive manufacturing: In the automotive manufacturing process, triangulation laser sensors are used for precise alignment in body welding, surface quality inspection before painting, and control of assembly accuracy of parts.
Robotics and automation: In robotic vision systems, laser sensors based on the triangulation principle are used for 3D reconstruction, posture estimation, and path planning, enhancing the intelligence of robots.
Solar photovoltaics: In the solar photovoltaic industry, triangulation laser sensors are used to detect surface flatness, cracks, and stains on photovoltaic panels, ensuring product quality and power generation efficiency.
Laser Displacement Sensors: High-Precision Measurement
Laser displacement sensors typically use the triangulation method. This measurement method can achieve nanometer-level precision, making it suitable for high-precision, short-distance measurements. In current industrial robot applications, triangulation is one of the commonly used techniques, with linearity reaching up to 1 micron and resolution up to 0.1 microns. Laser displacement sensors are commonly used to detect geometric quantities such as displacement, flatness, thickness, vibration, distance, and diameter of objects. These sensors play a crucial role in industrial manufacturing, precision machining, and quality control.
Measurement Range: 24 mm to 400 mm
Resolution: Min. 2 μm; Max. 75 μm
Protection Rating: IP64
Supported Interfaces: RS485 / Switch Output / Analog Current and Voltage
Measurement Range: 25 mm to 600 mm
Repeatability: Min. 10 μm, Max; 800 μm
Protection Rating: IP60
Supported Interfaces: RS485 / Switch Output / Analog Current and Voltage
Laser Distance Sensors: The Extensive Application in Industrial Automation
Laser distance sensors usually adopt the pulse method (ToF) or phase-shift method, and due to their suitability for a wider range of distance measurement needs, they are widely used in industrial production automation. These sensors not only meet the requirements for long-distance measurement but also feature high precision and fast response times. In the field of industrial automation, laser distance sensors are extensively used for position control and navigation, contour measurement and surface inspection, safety protection, logistics and warehouse management, as well as automated welding and cutting. They provide reliable distance measurement data for automation systems, helping to improve production efficiency, accuracy, and safety. They also demonstrate unique advantages in emerging fields such as intelligent transportation and autonomous driving.
Measurement Range: 0.1 m to 50 m
Distance Measurement Principle: Phase-Shift Method
Resolution: 1 mm
Protection Rating: IP67
Supported Interfaces: RS485 / Switch Output / Analog Current and Voltage
Measurement Range: 0.2 m to 100 m
Distance Measurement Principle: Phase-Shift Method
Resolution: 1 mm
Protection Rating: IP67
Supported Interfaces: RS232 / RS485 / Switch Output / Analog Current and Voltage
