Displacement Sensors / Measurement Sensors
What is a Displacement Sensor?
Displacement Sensor measures object distance through various elements, like optics or ultrasonics, converting it into distance data.
What is a Measurement Sensor?
A Measurement Sensor is a device that measures the dimensions of an object by converting changes in amount of light into electrical signals when the object interrupts a wide laser beam.
Features
1. The physical quantity of an object can be measured
A Displacement Sensor measures and detects changes (displacement) in a physical quantity. The Sensor can measure the height, width, and thickness of an object by determining the amount of displacement of that object. A Measurement Sensor measures the position and dimensions of an object.
2. Physical quantity output is also possible in addition to ON/OFF signal output
Analogue output of physical quantities (current output or voltage output) can also be performed (excluding some models). Some models also support digital (serial) communications.
Operating Principles and Classification
Displacement Sensors
1. Optical Displacement Sensors
Triangulation Measurement Method
These sensors use a triangulation measurement system.
Some sensors employ a PSD, and others employ an Imaging Device (CCD and CMOS) as the light-receiving element.
PSD Method
Light is focused on the object and reflected light is directed to a Position Sensing Device (PSD). Object movement alters the PSD’s output balance, allowing calculation of A/(A + B) using span coefficient “k” and offset “C.”
Imaging Device Method (CCD Method and CMOS Method)
A CMOS (CCD) sensor, unlike a PSD sensor, offers precise displacement measurement unaffected by object color or texture. It converts light intensity on individual pixels into distance when a spot beam reflects off the object’s surface onto the light receiving element.
Differences between CMOS and CCD:
CCD stands for Charge Coupled Device, and CMOS stands for Complementary Metal Oxide Semiconductor.
Regular Reflection Model and Diffuse Reflection Model:
Regular Reflection
A specular reflection is produced, such as from a mirror surfaced or glossy object.
Diffuse Reflection
A beam is reflected in all directions from an object with a standard surface.
Regular Reflection Model
Light from the object is directly received by regular reflection, and stable measurement is possible of metal and other objects with a glossy surface.
Diffuse Reflection Model
A perpendicular light beam is directed onto the object’s surface, capturing the diffuse light reflection for a broad measurement area.
Regular-reflective Sensor Heads receive direct light from objects, suitable for stable measurements on glossy surfaces. However, their measurement range is narrower than Diffuse-reflective Sensors. The latter use an angled Sensor Head, enabling measurement from a distance.
Line Beams and Spot Beams
Line Beam Model
This model measures the average displacement within a line beam. Depending on the measurement conditions, this model provides stable measurements without being affected by bumps or unevenness on the object surface.
Spot Beam Model
This model is more susceptible to the influence of bumps or unevenness on the object surface.
Confocal Principle
The confocal principle ensures that emitted and received light align along the same axis, allowing precise measurement of an object’s height. This method remains unaffected by material or object inclination, resulting in stable and high-resolution measurements due to the consistent waveform of received light.
White Light Confocal Principle
In the OCFL module, special lenses focus white LED light into distinct colors. Only the color reflected off the object is used to calculate distance. The Sensor Head handles color separation, while the Controller contains LED, spectroscope, and processor. This design eliminates the need for extra components, enhancing noise resistance and compactness.
Height is determined using wavelength, with the spectroscope in the Controller converting the reflected wavelength into distance.
OCFL Module
Omron’s OCFL module adjusts focal points for different light colors, ensuring a consistent spot size. This design, unlike triangulation, avoids spot size variation. Advanced lens technology enables a compact, drive-mechanism-free structure for precise measurements.
Light-cutting Method
A laser beam scans the object’s cross-sectional shape by projecting a band-like laser and capturing reflections with a CCD. Triangular distance measurements are used to calculate the object’s shape. This method simultaneously gathers 2D data for both the X and Z axes, eliminating the need to reposition either the sensor or the object.
2. Linear Proximity Sensors
AC current in a coil produces magnetic flux. Interaction with a metal object induces eddy currents, altering coil inductance. By analyzing this relationship, displacement distance can be calculated.
As the object gets closer to the Sensor Head, eddy currents increase, reducing oscillation amplitude. When it moves away, eddy currents decrease, increasing amplitude. Measurement relies on detecting these amplitude changes due to object position.
3. Ultrasonic Displacement Sensors
This type of sensor functions by transmitting ultrasonic waves towards an object and then receiving the waves after they bounce back from the object. It calculates the distance to the object by considering the time it takes for the ultrasonic waves to travel to the object and return, taking into account the speed of sound.
4. Contact Displacement Sensors
This type of Sensor measures displacement through direct contact of a measured object with the Sensor. It provides superior measurement precision compared with Contactless Sensors.
Differential Transformer Method
When the Sensor Head touches an object, it moves a core, creating a gap in coils. AC current alters coil impedance, resulting in a linear differential voltage output. This voltage helps determine the object’s displacement.
Magnetic Sensing Method
When the Sensor Head touches the object, a magnetic scale with north and south poles alternately positioned at a fine pitch inside the Sensor moves. The change in magnetic flux that occurs at this time is detected with a magnetic resistance sensor to determine the displacement.
Measurement Sensors
Optical Measurement Sensors
Measurement Sensors, which measure the widths or positions of objects, use one of the following three methods: light intensity determination, Imaging Device, or laser scanning.
All types of measurement sensors consist of an emitter and a receiver.
Interested to find out more about Omron Displacement & Measurement Sensors? Feel free to contact us!
