Contact-free Encoder in Potato Production

Turck’s QR24 encoder is demonstrating the superiority of its contactless measuring system on a buffer conveyor in the potato processing area at Schaap, a company based in the Netherlands

The weakness of many different encoder types is seldom due to the limits of the measuring principle, nor their electromagnetic compatibility or other interference factors; the drawback is mostly the mechanical system. At the potato processing plant of Schaap Holland B.V., Turck’s QR24 conctactless encoder monitors a buffer conveyor, saving technical personnel the need for complex mounting solutions and the regular maintenance of traditional encoders.

The positioning element turns itself behind the aluminum ring
Buffer conveyor: Up to 500 kilos of potatoes can be buffered on both belts
The stainless steel guard covers the entire motor together with the encoder during operation
The spring mounting of this encoder turned out to be susceptible to mechanical faults and wear
The two belts with the potatoes (in white) are visualized on the operator panel of the S7 controller

Fully integrated process

The potato producer Schaap Holland B. V supplies 45,000 tons of potatoes a year to commercial customers and the food service industry. The sorting, washing and peeling of the potatoes is largely automated. A continuous conveyor section takes the potatoes from the washing area into the refrigeration tunnel. In order to prevent the entire line to stop, Schaap uses buffer conveyors in front of the weighing system at the packaging machine.

QR24 monitors motor at buffer conveyor

When the packaging material has to be reloaded, the entire process no longer has to stop, since the buffer conveyor reduces its speed and compensates for the delay. A contactless inductive QR24 encoder from Turck has recently been installed to monitor the motion of the motor driving the belt. This enables up to 500 kilos of potatoes to be buffered in the process.

High mechanical stress

The shaft of the motor rotates slowly. The QR24 was therefore set to twelve pulses per revolution. The linear motion of the cooling conveyor has to be monitored with just one pulse every five centimeters. However, this presents us with a major mechanical challenge. The previously used incremental encoder based on the optical measuring principle had to be spring-mounted. It was mounted on the housing around the shaft with two small spring plates. “The stability and precision of these encoders were not an issue, but this previous solution brought with it some mechanical problems,” van Raalte explains. “Due to the vibration of the motor, the spring was always moving so that after two years it didn’t work any more.”

No need for bearings or spring couplings

With Turck’s contactless encoder, this is no longer a problem. Spring couplings are unnecessary since there is no mechanical connection between the shaft and the sensor unit. Only the position element is fastened directly to the shaft. “We have been looking for an encoder like this for years,” states Raalte. “When I saw the device on the title page of the customer magazine, I knew: we need something like this.”

Contact-free encoder QR24

On all QR24 models the sensor and the positioning element of the encoder are fully encapsulated and designed as two independent and fully sealed units that can withstand vibration or knocks on the shaft. Wear-intensive ball bearings or seals which lead to machine downtimes or long maintenance times are not required. The QR24 series thus has the edge over both optical and magnetic encoders.

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