You probably do not come from: Germany.  If necessary, change to: United States
  1. Homepage
  2. ToF PMD

Laser distance sensor with time-of-flight technology from PMD

The operating principle for precise measurement

The sensor uses laser to transmit a modulated light wave which is reflected back by the object to be measured. The phase position of the received reflected light signal is compared with the phase position of the transmitted light. Based on the phase shift, i.e. the "distance" between the wave crests, the time of flight of the light is determined and the distance between the sensor and the object is calculated.

  • Reliable photoelectric distance detection with long range
  • Very good reflection resistance and background suppression for reliable switching
  • High precision for the detection of small parts
  • Colour-independent measurement even with difficult surfaces
  • Versions with laser protection class 1 or 2

Precision within a millimetre

The PMD sensors from ifm use a "system-on-chip" design: Both sensor element and electronics for signal evaluation are integrated on a single silicon chip called a Photonic Mixer Device (PMD). Advantage: This innovative ifm design offers high measurement accuracy in a compact, industrially compatible housing – at a fraction of the price of conventional systems.

With the extremely small laser light spot, the sensors are perfectly suited for the detection of small parts, e.g. in error-proofing applications.

Detection of difficult surfaces made easy

What is particularly special about the PMD technology: The PMD sensors measure the distance irrespective of the surface colour. Even ambient light sources, reflective, oil film wetted surfaces or very dark objects are no problem. The impact angle of the object may be up to 20 degrees.

PMD sensors detect objects with laser protection class 1 which is uncritical to the eye. The excellent reflection resistance and background suppression, together with a high excess gain, enable reliable operation. The switch point is set easily and within a millimetre by means of user-friendly 3-button handling or alternatively via IO-Link. It also allows provision of the current distance value.

Triangulation technique with the PMD profiler

The sensor works by means of triangulation. For this purpose the sensor has a projection unit which projects a laser line onto the surface to be measured. This line is reflected and taken up again by a receiving element (PMD chip). Compared to the projection unit, however, the camera has a clear angular offset and can therefore detect the height profile.

The measuring range of the sensor is between 150 mm and 300 mm away from the sensor. Due to the perspective of the receiving element, the length of the laser line depends on the distance of the sensor to the target (the closer to the sensor, the shorter the line). Nevertheless, even if the distance between the sensor and the object changes, the proportions of the object remain the same. This means that the contour is measured independently of the distance. This makes the alignment and positioning of the sensor very simple.

3D sensor O3D with PMD time-of-flight technology

Time-of-Flight (ToF) By measuring the time of flight, the distance values between the individual pixels and the object can be detected at the same time as the grey-scale values at pixel level. This ensures that the 3D information is generated directly and in real time. The most common ToF technology is known as PMD (photonic mixer device).

The PMD time-of-flight technology ensures detection of scenes and objects with just one image capture of 23,232 pixels in three dimensions and without motion blur. The scene is illuminated by modulated, invisible infrared light and the reflected light hits the PMD sensor.