PDC Sensor for Edge Detection - Ultrasonic Web Edge Control with Fork Sensor Technology for Transparent and Light-Sensitive Materials
This technical article explores the ultrasonic web edge control technology using fork sensors, covering the operating principle of ultrasonic attenuation measurement, the calibration and teach-in procedures, the analog output signal processing, and the application-specific advantages for transparent films, paper, and light-sensitive materials.
The ultrasonic web edge control sensor operates on the principle of measuring the attenuation of an ultrasonic signal as a material web passes through a fork-shaped sensor gap. The fork's lower leg houses an ultrasonic transmitter, while the upper leg contains a receiver. The transmitter emits short, cyclical sound pulses that travel across the fork gap to the receiver. When a web material is introduced into the gap, it covers a portion of the sound path, attenuating the signal received by the receiver. The degree of attenuation is directly proportional to the amount of the web edge covering the sound path. The internal electronics evaluate the received signal strength and convert it to an analog output that represents the edge position within the fork's measuring range of 8 mm (±4 mm). The sensor's resolution of 0.025 mm enables precise edge tracking, essential for maintaining consistent web alignment in high-speed converting processes.
PDC Sensor
The calibration and teach-in procedures enable the sensor to be configured for specific web materials and edge positions. The sensor features a teach-in button on the top of the housing, which can be used to set the zero position of the edge. Two calibration options are available: clearing the fork opening of any web material and pressing the button for approximately 3 seconds until the two yellow LEDs flash alternately, or aligning the web edge inside the fork with the two marks to ensure 50% coverage of the sound path and pressing the button for approximately 10 seconds until the LEDs remain lit. The teach-in process ensures that the sensor's analog output corresponds to the desired edge position, simplifying setup and changeover. The sensor can also be parameterized using the LinkControl adapter and software for more advanced configuration.
The analog output signal processing converts the measured attenuation into a linear signal proportional to the edge position. The sensor provides both voltage (0-10 V) and current (4-20 mA) outputs, allowing compatibility with a wide range of control systems. The analog output varies linearly with the position of the web edge within the fork's measuring range, providing a continuous, real-time indication of the edge location. The response time of 4 ms ensures that the output tracks rapid edge movements, enabling responsive web guiding control. The three LEDs on the sensor housing provide visual indication of the web position within the fork, with the LEDs indicating whether the web is centered, left, or right of the desired position. For light-sensitive materials, the LEDs can be switched off to prevent interference.
The application-specific advantages of ultrasonic edge detection are most apparent for transparent films, paper, and light-sensitive materials. Ultrasonic sensors detect the edge based on the physical attenuation of sound waves, which is independent of the material's optical properties. This makes them ideal for controlling the web side of highly transparent foils, where optical sensors would fail due to light passing through the material. The sensors are also unaffected by paper dust pollution, a common problem in paper converting that can degrade optical sensor performance. The ultrasonic sensor's robust metal housing and sealed construction ensure reliable operation in harsh industrial environments. The sensor's ability to detect sound-absorbent materials such as foils and paper makes it suitable for a wide range of web materials, from thin films to heavy paper.
The future of ultrasonic web edge control is focused on enhanced connectivity and intelligent diagnostics. The integration of IO-Link communication enables remote monitoring of sensor status, signal quality, and diagnostic data, supporting predictive maintenance and reducing downtime. The development of sensors with multiple measurement channels is being explored to provide edge detection and width measurement in a single device. The ongoing advancement in transducer materials and signal processing is improving the resolution and accuracy of ultrasonic edge sensors, enabling even tighter web guiding tolerances. The ultrasonic edge sensor remains a cornerstone of modern web handling technology, providing the reliable, non-contact edge detection required for efficient converting, printing, and packaging operations.
