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Ultrasonic sensors – life without them is unimaginable in today's paper, printing and packaging industries

Ultrasonic sensors – life without them is unimaginable in today's paper, printing and packaging industries

13 April 2012

microsonic GmbH: Ultrasonic sensors have set new standards in automation technology. In particular in the paper, printing and packaging industries, they have become essential. These industries often use materials whose particular properties quickly push other sensors, such as optical or inductive sensors, beyond their comfort zone. Ultrasonic sensors, on the other hand, can measure even through dusty air or dye fog. Even thin deposits on the sensor membrane, such as paper dust, have no negative effects on sensor function. In a wide variety of applications, these robust sensors are particularly attractive due to their ability to measure without contact or touch, as well as their precision detecting capability for objects of different materials and colours.

The ultrasonic principle (echo propagation time measurement):
The ultrasonic sensor periodically beams out a short, high-frequency sound pulse. This propagates through the air at the speed of sound. When it strikes an object, it is reflected, returning to the sensor as an echo. The ultrasonic sensor uses the period of time between transmission of the sound pulse and receipt of the echo signal to calculate the distance to the object. Since the distance to the object is determined by measuring the sound propagation duration and not by measuring intensity, ultrasonic sensors are outstanding at masking background. Nearly all materials that reflect sound can be detected. Whether fill level measurements in dye trays, stack height detection or the determination of the winding diameter of transparent or highly reflective web material, a proximity switch based on an ultrasonic sensor can solve any of these specific applications reliably.

Ultrasonic sensors also offer another functional principle that allows them to solve special measurement problems – amplitude evaluation. This feature is used in ultrasonic double sheet controls as well as in label and splice sensors and ultrasonic edge sensors. All together, these contribute to a reduction in holding time, avoidance of errors in the processing process and prevention of damage to the machine due to a premature signal.

Ultrasonic amplitude evaluation:
This principle allows ultrasonic transmitters and receivers to be housed separately in opposing housing elements; the sensor works in so-called flank mode. The transmitter sends a high-frequency sound pulse, which is analyzed by the evaluation electronic in the receiver. Based on the signal level received, it can make conclusions about the material situation. The evaluation electronics convert this information into a corresponding output signal.

In the ultrasonic double sheet control
For example, an extremely high-frequency ultrasonic transmitter beams sound from the underside against the material to be detected. The signal transmitted induces vibrations in the material sheet. These cause the propagation of a very small sound wave on the other side of the sheet. If there are overlapping (double) sheets, the signal is damped even more. The ultrasonic double sheet control can thus reliably display the sheets "Single sheet", "Double sheet" and "Missing sheet", thus preventing errors in the printing or packaging process.

1999 marked the first time a well-known printing machine manufacturer used the microsonic dbk-4 double sheet control in their sheet printing machines. Since then, the application area has grown far beyond printing presses and double sheet control using ultrasound is simply essential for the paper, printing and packaging industries. The new generation, the dbk+4 from microsonic, combines multiple variants of the previous model into a single device: Three predefined working ranges can be selected – and switched during ongoing processing. An LED signals whether the user has pre-selected the right working range. A trigger mode for shingle feeders is also included. The significantly reduced housing dimensions, as well as variants with an angle head, external receiver converters or small M12 heads, optimise integration into the machine.

Ultrasonic label and splice sensors
work on the same principle as double sheet controls. The backing material transmits a different signal level from the label or the splice. This signal difference is evaluated by the sensor. Even for very slight differences between the substrate material and the label, or web material and splice, the sensor can reliably detect them using a separate teach-in. Even inaccessible splices can be detected reliably after a simple learning of the web material.

Ultrasonic edge sensors
are designed as fork sensors and also work as one-way barrier. A material entering the fork covers the sound gap between the transmitter and the receiver, damping the signal received. The internal electronics evaluate this and emit an analogue signal that depends on the degree of coverage. Ultrasonic edge sensors are used for edge control in paper, printing and packaging machines, where they reliably detect the edges of noise-opaque materials such as film or paper. This makes them perfectly suited for web guidance control of high-transparency films and light-sensitive materials. But materials with highly variable transparency, increasingly widespread in the packaging industry today, or paper types with a high dust output are simple to detect with ultrasonic edge sensors.

And if that's not enough, the industry can continue to anticipate additional innovations in future from this internationally known ultrasonic specialist headquartered in Dortmund's technology park.

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