Apple harvesting is largely manual work. Harvesters pick the apples on self-propelled scaffolding or harvesting machines. Two ultrasonic sensors are attached to the front left and right of the self-propelled scaffolding. The analog sensors measure the distance to the row of trees and transmit the values to the control system as a distance-proportional signal, which is used to automatically steer the self-propelled scaffold and keep it on track.

Insensitive measuring principle

Dusty environments on the orchard and possibly thin dirt deposits on the sensor membrane as well as a damp environment on the water conveyor belts in the wine press do not impair the sensor function. As the sensor membrane vibrates slightly due to the sound frequency, it repels drops of liquid, dust and the like.

Even air currents do not affect the measuring accuracy. Dust and mist can attenuate the sound signal and, under certain circumstances, slightly reduce the maximum range of an ultrasonic sensor. In most cases, however, a measurement is still possible. Only at constant, hot ambient temperatures or object temperatures of over 85 °C does the ultrasonic principle reach its natural performance limit.

The standard measuring principle for an ultrasonic sensor is echo transit time measurement: the sensor emits a high-frequency sound pulse cyclically, which propagates through the air at the speed of sound. If it hits an object, it is reflected there and the echo returns to the sensor. The ultrasonic sensor calculates the distance to the object from the time span between emitting the sound and receiving the echo.

Level measurement in the juicer

The label sensor 'esf-1/CDF/IO-Link' is equipped with a pnp switching output and a push-pull switching output with IO-Link interface. This allows it to be set directly on the controller without having to operate the sensor on site.

© Microsonic

The washed and crushed apples are pressed in the juice press of the juice pressing plant. The fill level of the mash must be continuously recorded in the feed to the juicer. To calculate the fill level, an analog ultrasonic sensor - such as the 'crm+' from Microsonic - transmits a distance-proportional analog signal to the control system. The chemical-resistant sensor also measures reliably in damp environments and the resistant PEEK film protects the membrane against contamination and caking.

The sensor covers a measuring range of 30 mm to 8 m with five scanning ranges. Its digital display outputs measured values directly.

Regulation of the volume flow of bottles

Apple juice is often bottled in glass or plastic bottles. Conveyor belts transport the empty, cleaned bottles to the bottling plant. The ultrasonic sensor 'lcs-35/DDD/QP', for example, is used on conveyor belts with widths of 300 to 600 mm to detect the transparent bottles - as optical sensors reach their detection limits with glass and plastic bottles when it comes to material and transparency.

The empty bottles, which reach the filling system via a conveyor belt, should be fed in evenly. This regulation of the volume flow is carried out by the ultrasonic sensor, which covers three different states thanks to three switching outputs: if it detects no bottles on the conveyor belt, it is stopped to save energy. If the sensor detects too few bottles on the conveyor belt, the control system allows the conveyor belt to run faster to ensure an even filling process. Conversely, the control system reduces the speed of the conveyor belt to avoid a bottleneck in front of the filling system.

The right label

Once the apple juice has been bottled, each juice bottle is given a label that adheres to a carrier material wound onto a coil. In the labeling process, the labels are unwound from the coil, detached from the backing material at the dispenser edge and applied to the bottles with a pressure roller. An ultrasonic label sensor - such as the 'esf-1' from Microsonic - can be mounted close to the dispenser edge. During the ongoing process, the fork sensor detects whether a label is present on the carrier material and can be dispensed.

Ultrasonic label sensors work according to the principle of amplitude evaluation. Ultrasonic transmitters and ultrasonic receivers are positioned opposite each other; the web material is passed between the transmitter and receiver without contact. The transmitter continuously emits sound pulses that penetrate the web material and are attenuated in the process. The receiver picks up the attenuated signals, the evaluation electronics analyze them and the received signal level can be used to draw conclusions about the material situation. The carrier material provides a different signal level than a label or even a splice, so that the sensor can evaluate the signal difference. Even a splice that is inaccessible in the roll can be reliably detected by teaching in the web material.

Innovative materials and eye-catching label designs are a challenge for sensor technology - but not for ultrasonic sensors: More and more foil labels are being used instead of paper labels, and changing colors of bottle labels are in demand - such as transparent, black or metallized foils or finishing options using high-gloss varnishes or soft-touch coatings.

Author:
Melanie Harke is Head of Marketing at Microsonic.