Functionality and technology of optical distance sensors

Triangulation

The distance measurement is based on the triangulation principle. The laser beam strikes the object as a small point. The receiver of the sensor (photodiode line) detects the position of this point. The angle of incidence changes according to the distance, and thereby the position of the laser point on the receiver. The photodiode line is read by an integrated microcontroller. The controller accurately calculates the angle from the light distribution on the photodiode line and then calculates the distance to the object from this. This distance is either issued at the serial port or converted into an output current proportional to the distance. The microcontroller guarantees a high degree of linearity and measuring precision. The combination of a photodiode line and a microcontroller permits interfering reflections to be suppressed and thereby provides reliable data from critical surfaces. The sensor adapts to different colors by adjusting its internal sensitivity, making it virtually independent of the color of the object. A digital output is activated if there is no object within the measuring range or if insufficient light is received to correctly detect the object, e.g. if the sensor is dirty. The possible resolution and accuracy change with the distance. The same distance Δd which causes a large change in the angle α1 close to the sensor produces a much smaller change in the angle α2 at a greater distance (see drawing). This non-linear behavior is corrected by the microcontroller, so that the output signal remains linear to the distance.

Products: Laser distance sensors

Measuring functions

Distance measurements

In the case of distance measurement, the sensor is ready to use immediately and gives the distance from the sensor to the object. The measured value can, for example, be used for the precise positioning of objects or for controlling a system. A digital output can also be parameterized as an option.

Tolerance measurement

If, for example, the dimensional accuracy of objects is to be checked, a direct tolerance measurement can be made by teaching-in a reference, thus allowing the deviation from the nominal dimension to be determined directly. Here too, a digital output can be parameterized accordingly.

Beam shapes

Besides different dimensions and ranges, the beam shape plays a particularly important role. Thanks to continuous further development, Baumer can now offer three different beam forms in its portfolio with the new «multi-spot» measuring principle:

Laser point

Accurate measurement of small objects thanks to focused laser spot < 0.4 mm

Laser line

Stable measurements on rough surfaces and textured color surfaces thanks to a fine laser line < 10 mm

Multi-spot

Stable measurements on inhomogeneously shiny and very rough surfaces from over 600 measurements with an extra-long laser line < 72 mm

Focus ranges

Laser distance sensors enable high-precision distance and position measurement with a resolution of less than one micrometer. In practice, however, there are interference effects that can reduce the repeatability of optical distance measurements. With the introduction of selectable focus ranges, Baumer OM70 laser distance sensors enable significantly better local repeatability and thus ensure more reliable measurement results and higher process reliability for automated measurement tasks.

Special features

High ambient light immunity

Powerful algorithms integrated in the sensor make laser distance sensors very insensitive to external light sources. This guarantees reliable, robust operation.

Automatic exposure control

Optical distance sensors by Baumer automatically adapt to different object colors and brightness levels by varying their transmission intensity and optimizing their exposure time. This they are not affected by the reflectivity of an object. It is also possible to measure objects with a reflectivity of up to 2%.

Synch-In / Triggering

The measurements of several sensors can be synchronized through the sync-in input. For thickness measurements, two sensors can be triggered simultaneously in synchronous mode through the sync input. In asynchronous mode, on the other hand, several sensors that interfere with each other in an application can deliberately be operated one after the other.

Programmable filter functions

The noise of the output signal can be reduced by activating filtering, thus increasing the resolution. The filter is used to suppress measurement errors. The output changes only after a defined number of measured values. The measuring frequency is not affected by this filter, but the response time is. The filter function can be parameterized through the selection of predefined precision modes.

Programmable measuring ranges

The measuring range can be adjusted by the user within the maximum measuring range with the teach-in button, the teach-in line or through the display. The analog output has its full stroke within this taught-in area and thus higher measuring accuracy. The factory setting is the maximum measuring range.

Configurable switched output

A switched output should switch as soon as a defined measured value exceeds or falls below the set level. For a reliable switching signal, the hysteresis (difference between the switching point and the return switching point) can be parameterized in millimeters in absolute terms. The safe operation of your system is guaranteed, regardless of the position of the object in the field of view.

Time-of-Flight / Run time measurement

With the run time measurement method distances are measured indirectly by measuring the time required by a signal to travel the length of the range to be covered. This translates into the real world as follows: a sender unit is emitting a burst signal which, when reflected by an object, is picked up by the sensor's receiver. The sensor's electronics evaluates the time elapsed and/or the phase-shift encountered which is then converted into distance information. By applying the run time technology objects can be detected precisely and reliably even at long distances.

Multi-spot light section sensors

The innovative multi-spot measuring principle by Baumer is based on light section technology. Up to 600 measuring values of an object are determined per measurement in the sensor, and from these values the distance is calculated using the intelligent evaluation process. Thanks to its resolution of up to 2 µm at a measuring frequency of 500 Hz, the sensor offers stable and precise measurement results.

Products: Edge and height sensors

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