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The air traffic control radar or the lidar in meteorology - both methods are based on the same principle: A signal is radiated and reflected by the object to be measured. By measuring the transit time measurement, it is very easy to deduce the distance. This so-called time-of-flight method is also the basis for the new one Distance sensors of the PMD OGD series by IFM Electronic.

Positions or distances must be determined in numerous industrial applications. Automated assembly systems, warehouse logistics systems and production machines are just a few examples. The demands placed on the sensors can vary greatly. Accuracy, speed, ruggedness, immunity to interference, etc. are the typical characteristics that sensors must have.

Transit time measurement with laser light

A very accurate and at the same time very fast method to measure the distance is time of flight (TOF). The PMD OGD sensors work according to this method. The sensor emits modulated red laser light of the laser class 1 and determines the time required for the light from the sensor to the object and back again. In this way, the distance to the object can be determined easily and with high accuracy.

The sensors are available in two versions: The PMD OGD Longe Range version is suitable for measuring distances up to 1500 mm and is used, for example, in material handling applications in warehouse logistics. The PMD OGD Precision version can measure distances up to 300 mm and determines them with millimeter precision. The sensor has a light spot diameter of about 1 mm, depending on the scanning distance, so that even small parts can be reliably detected. This makes the sensor particularly suitable for applications in automated assembly, where it can be used, for example, in so-called error-proofing applications.

He can check the correct assembly of the smallest parts. Such inline quality checks not only ensure high quality assembly, but also help to reduce costs. In general, the later an error is detected, the higher the resulting costs. If the error is only discovered in a final quality control or - worse still - only after the delivery to the customer, the effort for the correction of the error is very large. On the other hand, if a suitable sensor recognizes the fault immediately after the faulty assembly step, it can be fixed relatively easily. Alternatively, the affected part can be removed from production.

Tested in own production

ifm20918How well the PMD OGD Precision can be used for inline quality checks has been demonstrated by the manufacturer in its own sensor manufacturing facility in Tettnang. Sensors are assembled in an automated assembly line in production. In this case, a sealing ring must be inserted before assembly to ensure the necessary high degree of protection. Missing this seal, this is not necessarily noticed during assembly. The incorrectly mounted sensor works, but it is not sufficiently protected against penetrating moisture. If such a sensor were delivered, depending on the environmental conditions it would lead to a failure and a complaint by the customer. The presence control of the sealing ring was realized in test stations with the PMD OGD Precision. The sensor was able to detect with 100-percent reliability whether the sealing ring with a thickness of only 2 mm was inserted in the groove provided for this purpose.

Since the TOF measurement method is very robust against disturbances, this reliability can be achieved even under difficult environmental conditions. For example, stray light sources are not a problem. The measurement also works regardless of the color of the surface. The presence control of small components in automated assembly described above also works for surfaces where other sensor principles are poorly applicable. Typical examples of this are reflective surfaces, wetting of the surface with an oil film or very dark objects, as in the sealing rings described above.

Compact problem solver easy to use

The PMD OGD series sensors are housed in a compact housing that can easily be mounted with an M18 thread. As an alternative to this standard mounting two holes can be used on the housing. The highly visible red laser spot makes setting up the sensor very easy. On the back of the case, the PMD OGD has a display and three buttons for operation. This makes the device very comfortable. During operation, the display shows the current measured value for the distance, the illumination of the display changes between red and green depending on the switching status of the sensor. Two LEDs on the top of the housing also indicate the switching state, so that it is instantly recognizable in the application from all directions.

Flexible with IO-Link interface

Like most of the manufacturer's sensors, the PMD OGD is equipped with an IO-Link interface. This not only transmits the measured value, but also allows the sensor to be parameterized from an IO-Link master. This makes the PMD OGD even more flexible in the application. If, for example, the production is changed for the assembly of different products, the sensor is simply provided with the new parameterization - the production can be continued directly afterwards. This allows the production environment to be adapted very flexibly. The IO-Link interface also offers advantages for maintenance and service: If the sensor has to be replaced once, the parameterization can simply be transferred to the replacement device. Downtime is significantly reduced.

Integration in industrial 4.0 applications

The IO-Link interface simultaneously guarantees seamless communication with higher-level systems. This makes it easy to implement industry-standard 4.0 concepts, which require continuous communication from the sensor level to the cloud, with the new PMD OGD sensors.

Picture above: The presence of the smallest parts in the assembly - for example, a sealing ring in a sensor housing - can be safely checked with the PMD ODG.

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