Precise material management in various conditions

July 13th, 2018, Published in Articles: PositionIT

Time-of-flight laser technology offers reliable measurements of a variety of materials in a range of visibility conditions on a conveyor belt. This technology can also be used to monitoring conveyor belts for slippage and uneven loading.

The Bulkscan LMS511 from SICK Automation uses time-of-flight laser technology to provide non-contact volume flow measurements on conveyor belts. Regardless of the bulk material type and weather or visibility conditions, the multi-echo technology in the sensor allows it to generate reliable volume flow signals using the laser’s time of flight and the conveyor belt speed.

This calculates total quantities of mass and flow. The sensor monitors conveyor belt operation without making belt contact and provides prompt warning of any belt slippage. An integrated bulk materials centre-of-gravity calculator detects uneven loading, preventing excessive belt wear, and an integrated heater ensures safe operation at low ambient temperatures. These and other benefits make this scanner suitable for most bulk material types, including uncommon types.

Fig. 1: The Bulkscan LMS511 laser scanner.

Fig. 1: The Bulkscan LMS511 laser scanner.

Case study: Concrete dye

The Inorganic Pigments Business Unit at Lanxess manufactures over 100 colour shades to dye concrete materials. Concrete is dyed with synthetic iron oxide and chromium oxide pigments which allows for colour in projects like hotel facades or waterside paving stones, for example.

At its production site in Krefeld-Uerdingen, Germany, the manufacturer uses five Bulkscan LMS511 laser volume flowmeters to optimise the processes used for transporting high-quality iron chips. Using an oxidation and chemical precipitation process, colour pigments are obtained from the chips over a period, which are transported to the individual processing stations on conveyor belts while the transformation process occurs. A solution to guarantee the quantity and volume of material transported, as well as provide sensible control of the metering flow over a work day, was needed.

These requirements amounted to a non-contact measuring principle, traditionally a challenge for optical devices in the environments in which Lanxess operates. Detecting dark iron chip masses on dark conveyor belts under difficult lighting conditions is one of them.

Fig. 2: The laser scanner installation above the conveyor belt for continuous height profile measurement.

Fig. 2: The laser scanner installation above the conveyor belt for continuous height profile measurement.

SICK proposed its LMS511, a fast sampling technology that enables high precision laser measurement in almost all weather and ambient conditions. Called five-echo technology, it is suitable for applications needing reliable detection of dynamic objects in changing or unfavourable conditions. This includes applications with poor visibility such as in tunnels or in mines. In addition to maintaining good visibility in unfavourable conditions, five-echo technology is also very accurate.

Lanxess has a classic control loop at two locations. The laser scanners supply them with the current actual value for the quantity being transported on the conveyor belt and set point values are used for control at certain points. The measurement supplies the actual value and the controller then adapts the desired quantity by means of the speed of the first screw conveyor. This results in a constant transport flow.

The laser scanners are mounted at five locations above the conveyor belt and continuously measure the height profile of the iron scrap passing beneath using laser pulsing.

A notable aspect of this design is the reliable detection of the height profile, even with external interference factors such as dust or bulk material suspended in the air. This is possible due to new signal analysis technologies, which filter out the correct height profile signal from a large number of echoes. The software algorithm determines the correct signal from the various reflected laser pulses and, at the same time, suppresses any haze that might interfere with the measurement.

Fast scanning frequencies, up to 75 Hz, and fast response times are used to achieve maximum resolution for the height profile (and thus high measurement accuracy). They also enable the measurement of conveyor belts at speeds of up to 30 m/s.

The Bulkscan system offers six individually assignable switching outputs for additional signal processing, such as a warning or impulse output or as continuous outputs for measured value transmission over Ethernet. Processing and measured value preparation take place directly in the sensor, which also has two inputs. No additional data acquisition system is required.

Contact Robert de Scánde, SICK Automation South Africa, Tel 011 472-3733, robert.descande@sickautomation.co.za