Measuring the volume flow of bulk on conveyor belts - Het meten van de volumestroom van bulk material op lopende banden

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Delft University of

Technology

FACULTY MECHANICAL, MARITIME

AND MATERIALS ENGINEERING

Department Marine and Transport Technology

Mekelweg 2

2628 CD Delft

the Netherlands

Phone +31 (0)15-2782889

Fax

+31 (0)15-2781397

www.mtt.tudelft.nl

This report consists of 29 pages and 3 appendices. It may only be reproduced literally and as a whole. For

commercial purposes only with written authorization of Delft University of Technology. Requests for consult are

only taken into consideration under the condition that the applicant denies all legal rights on liabilities concerning

the contents of the advice.

Specialization:

Transport Engineering and Logistics

Report number:

2015.TEL.7990

Title:

Measuring the volume flow of bulk on

conveyor belts

Author:

J. de Lange

Title (in Dutch)

Het meten van de volumestroom van bulk material op lopende banden

Assignment:

Research

Confidential:

no

Initiator (university):

Dr. Ir. Y. Pang

Supervisor:

D. MSc D. He

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Student:

Job de Lange

Assignment type:

Experiment

Mentor:

Dr. Ir. Y. Pang

Report number:

2015.TEL.7990

# ####

Specialization:

TEL

Confidential:

No

Creditpoints (EC):

15 Subject: Material Flow Measurement for Belt Conveyors

The volume and flow rate of the material transported by belt conveyors indicate the operation status

and efficiency of a material handling system. To measure the material flow on the belt can be

considered to be the initial input for the control of material handling processes. In this industry field,

several technologies have been proven to be successful, which include tine measurement device of

Bulkscan LMS-511 (SICK B. V.).

This assignment is to test the above mentioned measurement device for belt conveyor operations. It

is aimed to determine the accuracy and feasibility of this scanner in various operational conditions.

The research in this experiment assignment should cover the following:

• Survey of currently available technologies to measure material flow;

• Functional description of the bulk scanner;

• Experimental setup and test results of the bulk scanner;

• Feasibility regarding applying the bulk scanner to measure dry bulk materials in different conditions.

It is expected that you conclude with a recommendation for the application opportunities based on

the results of this study.

This report should be arranged in such a way that all data is structurally presented in graphs, tables,

and lists with belonging descriptions and explanations in text.

The report should comply with the guidelines of the section. Details can be found on the website.

The mentor.

Dr. ir. Y. Pang

FACULTY OF MECHANICAL, MARITIME

AND MATERIALS ENGINEERING

Department of Marine and Transport Technology

Mekelweg 2

2628 CD Delft

the

Netherlands

Phone +31 (0)15-2782889

Fax +31 (0)15-2781397

www.mtt.tudelft.nl

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Measuring the volume flow of bulk

on conveyor belts

Testing the influence of several parameters on the accuracy

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I

Summary

Due to the invention of conveyor belts, and the rapid grow of industry; measuring bulk

material flows can be of big importance. Many different approaches were found to tackle this

problem. From a literature study it was derived that one of the most promising methods to

measure bulk is the use of laser-assisted techniques. Therefore, this research focuses on a

machine that uses laser beams to measure the volume of bulk material. For this device, the

Bulkscanner, the feasibility will be researched. The following research question should help

to achieve this goal:

“What is the feasibility of the Bulkscanner and how can the accuracy in measuring a volume

be approved”

To answer this question two experimental setups were made. One at standstill, a static setup,

in which the area of Duplo bricks was measured. The reason this setup was chosen is because

a static setup eliminates a lot of unknown disturbances and makes it thus easier to investigate

a single parameter. The second setup was designed as a more realistic setup. It consisted of a

conveyor belt and the Bulkscanner was used to measure the volume of Dorsilit sand and wood

pellets. This is a dynamic setup.

From the first static experiment it was derived that the Bulkscanner is not very good in

measuring material with sharp edges. Triangular shaped material gave better results than

rectangular shaped material. Explained was that this could be because of the algorithm the

Bulkscanner uses to calculate an area. The position of the Bulkscanner also had a significant

influence on the accuracy of measuring an area. Out of three distances tested at the static

setup 0.75 m was the most optimal bulk to Bulkscanner distance. Also it was shown that

darker background colours result in better measurements and a reflective background like

aluminium foil gave the worst results. At the best experimental conditions the accuracy was

higher then the minimum accuracy stated by the manufacturer which shows that the device

operates well in this experimental setup.

With the dynamic conveyor belt setup it was shown that measuring Dorsilit sand gave better

results then measuring wood pellets. Also, it was shown that putting the Bulkscanner closer to

the conveyor belt gave better results within a certain bandwidth. Finally, it was shown that the

speed of the conveyor belt also influences the accuracy. The results show that it is likely that

the higher the conveyor belt speed the less accurate the measurements. At the best

experimental conditions the accuracy was higher then the minimum accuracy stated by the

manufacturer. However for a lot of the results the accuracy was not as good as specified by

the manufacturer. This shows that the device does not perform as well as desired under these

specific experimental conditions.

In conclusion, this research showed the feasibility of the Bulkscanner in determining the area

of bulk at the static setup and the volume at the dynamic setup. At the static setup the

Bulkscanner performed well but at the dynamic setup the results were not satisfactory. For the

parameters bulk shape, Bulkscanner position, background colour, bulk material type, and

conveyor belt speed, an optimum was found within a certain bandwidth which can be used

when the Bulkscanner needs to be implemented in a system.

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III

1 Introduction

1.1 Background

Measuring bulk material can be of big importance in certain industrial processes. Especially

with the invention of conveyor belts, knowing the volume flow has a lot of uses. One of them

is that the volume flow can be monitored and regulated. This can help to ensure that the right

amount of material is available further up the process. If too much material is transported the

belt speed can be adjusted. By doing this peak loads will be avoided which results in energy

and maintenance savings. According to (W. Daus, 1998) these costs can be reduced by

respectively thirty and twenty per cent.

The literature study in chapter 2 shows that one of the most promising methods to measure

bulk is to use laser-assisted techniques. The advantages are that there is no wear due to the

lack of mechanical contact, it is easily implementable in an existing system, it works in a

broad temperature spectrum, and changes in material properties can be easily taken into

account. This report will focus specifically on one type of device that uses a laser. The

Bulkscanner LMS-511.

The Bulkscan LMS-511 is a device that uses a laser beam to measure bulk material. It is a

commercially available device that has already been successfully implemented in many fields.

Some implementations are shown in Figure 1-1. In Figure 1-1a the Bulkscanner is used to

measure the volume flow of a conveyor belt. In Figure 1-1b the Bulkscanner is used to create

a 3D image of a truck in front of a tunnel. Infrared sensors measure the temperature of the

truck and the generated 3d model is used to determine whether a truck is too hot to safely

enter a tunnel. In Figure 1-1c the Bulkscanner is mounted on an automatic guided metro that

is used to vacuum clean metro tunnels. The scanner creates a 3D image of the tunnel so the

robotic vacuum cleaners know the position of obstacles in the tunnel so that they do not bump

into them.

1.2 Scope

This research focuses on the use of the Bulkscan LMS-511 to determine the volume of the

material it measures. Other measuring systems will be discussed shortly so that the reader will

be familiar with them and will be able to compare the different systems. The device will be

tested under two conditions namely static and dynamic. For these two conditions the accuracy

is measured and the results will be used to determine the feasibility of the device under these

specific experimental conditions.

a) Measuring volume flow

b) Measuring the shape of vehicles c) Measuring the shape of a tunnel

Figure 1-1 Implementations of the Bulkscan LMS-511 (Sick insight, 1)

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2

1.3 Research goal

The goal of this research is to gain familiarance with the Bulkscan and to gain the knowledge

to successfully conduct experiments with the device. By answering the following research

question this goal should be met:

“What is the feasibility of the Bulkscanner and how can the accuracy in measuring a volume

be improved”

The following sub questions will help answer the main question:

• What kind of impact do material dimensions have on the accuracy of the Bulkscanner

• What kind of impact does the position of the bulk scanner have on the accuracy

• What kind of impact does the background colour have on the accuracy of the

Bulkscanner

• What kind of impact does the belt speed have on the accuracy of the Bulkscanner

Before these sub questions can be answered, an accurate experimental setup is necessary. The

first step is thus to design an experimental setup and to improve its accuracy.

With the experimental setups was found that the static setup is feasible. The Bulkscanner had

a higher accuracy then the minimum accuracy stated by the manufacturer. The best results

were measured with a triangular shaped material from half a meter distance with a dark

coloured background.

For the dynamic experiment the Bulkscanner did not gave sufficient results. Some results

were within the minimum accuracy given by the manufacturer, but overall most results were

not. The most accurate measurements were generated with the scanner 0.75 meters above the

conveyor belt, the material Dorsilit sand, and at the lowest belt speed.

1.4 Report structure

Before the research question can be answered a short literature review of the available

measuring systems is conducted. Explained is which method is chosen for this research and

why. Then, will be explained how the Bulkscanner works. This is done in chapter 2. The next

step is to make an experimental design. The different steps that need to be undertaken in order

to come up with a good experimental design are discussed in chapter 3. Explained is how the

experimental setup is designed and that its design is improved after analysing the first

measurement results. Chapter 4 states the experimental steps that have to be taken to

successfully conduct an experiment. In chapter 5, an overview is given of the experiments

that have to be conducted to answer the main research question and the sub questions. In

chapter 6 all results are shown and discussed. And finally, in chapter 7, the conclusions and

recommendations are given.

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3

2 Measuring systems

There are many possibilities to derive the weight of bulk material that passes through on a

conveyor belt. In this chapter the possibilities that were found in the literature on this topic are

discussed. When possible, the accuracy and the possibilities of the system are categorized to

give a clear overview. In paragraph 2.1 the possibilities to directly weigh the bulk material are

given. In paragraph 2.2 until 2.4 measuring systems are discussed which could be used to

calculate the weight of the bulk material. In paragraphs 2.5 until 2.7 the chosen device is

explained.

The first distinction that needs to be made is the distinction in continuous weighing options

and batch weighing options. Continuous weighing means that the weighing is incorporated in

the system and the weighing is done without interrupting the system. Batch weighing is done

on a separated track or at standstill. Most of the time the weighing is not continuous and only

small samples get weighed.

The method that is used to weigh the bulk material can also differ. Solutions relying on load

cells or strain gauges are discussed in paragraph 2.1. In paragraph 2.2 the possibility to weigh

material using radiation is discussed. A research that measures the mass of the bulk by putting

a known perturbation on the system is discussed in paragraph 2.3 and in paragraph 2.4

solutions using lasers are discussed. In paragraph 2.5, 2.6, and 2.7 the device that will be

researched is discussed into detail.

2.1 Weighing using load cell/strain gauge

The most straightforward way of measuring the amount of bulk on a moving belt is using load

cells (Ooms & Roberts, 1983). An example is depicted in Figure 2-1a (AccurateFeeders,

2001). A distinction is made between single idler systems and multiple idler systems.

Equipping multiple idlers with load cells will increase the accuracy. Literature stated that the

accuracy of single idler systems can reach up to a deviation in the weight measurement of

only one or two per cent (Ooms & Roberts, 1983). Multiple idler systems have a higher

accuracy of a half per cent deviation or even better.

Implementing load cells in an existing system can be hard. To tackle this problem, instead of

using load cells, strain gauges can be placed on an idler system (Ooms & Roberts, 1983). The

deflection of the idler, due to the weight of the bulk material, can be measured. This

deflection can be used to determine the mass of the bulk material.

2.2 Measuring using radiation

Materials can also be weighed by using nuclear devices (Colijn, 1975). A source of gamma or

beta radiation radiates through the material, which needs to be weighed. On the other side of

the material an ionization gage measures the amount of radiation that is not absorbed by the

material. For this method the absorption coefficient from the material has to be known. An

implementation of this method in a mine is shown in Figure 2-1 (Branch, 2015).

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4

2.3 Measuring using a perturbation

Dierks (1990), suggested a interesting approach to measure bulk material. By putting a known

perturbation on a conveyor belt, the kinetic energy of the conveyor belt and bulk material was

registered. From this kinetic energy, the mass of the total system was derived. By subtracting

the mass of the conveyor belt system, the mass of the bulk material is known. For different

setups the deviation between the real mass and the measured mass was between 0 and 24 per

cent.

2.4 Measuring using laser

Another option is to use lasers to measure the amount of material on a conveyor belt (Dunker,

2013). The laser scans a cross-section perpendicular on the conveyor belt. If this is done

continuously a volume flow is measured. With the right density the mass can be calculated.

This method is very promising because it can measure continuous, is easy to implement, and

according to the manufacturers it can be very accurate. An example is depicted Figure 2-1c.

Here a device of the company Sick is placed above a conveyor belt (Sick.com, 2015).

This research focuses on this method. An existing device that is available on the market is

used. In the next paragraphs the measuring principle of this system is explained.

2.5 Basic working principle of the Bulkscanner

The Bulkscanner uses a laser beam to determine the distance to the material it is measuring.

The device sends a laser beam to this material. The material reflects the beams and the device

receives them back. The time it takes for the beam to reach the material and reflect back to the

device can be used to determine the distance to the material. The laser beam rotates at a

certain frequency to be able to scan the total surface instead of only one coordinate. Every

angle will give a new coordinate. This principle is depicted in Figure 2-2. Where the angle of

the beam is φ. The coordinates the Bulkscanner receives are used to determine the surface of

the material.

a) Load cell b) Radiation

c) Laser

Figure 2-1 Different measuring systems

φ

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5 First, the device is calibrated by measuring an empty conveyor belt so the area between the

Bulkscanner and the conveyor belt is known. Then the Bulkscanner measures the area

including bulk material on the conveyor belt. By subtracting the two measured surfaces from

each other the surface of the bulk material is known. This principle is graphically shown in

Figure 2-3.

If the surface, with units [m

2

] of the bulk material at a certain time is known, the belt speed is

known [m/s], the time a conveyor belt is operational [s], and the bulk density [kg/m

3

_{] is also}

known, the following parameters can be given as output (Sick, 2012):

• Volume [m

3

]

• Mass [kg]

• Volume flow rate [kg/s]

• Bulk density [kg/m

3

]

• Centre of gravity [-]

The actual device is shown in Figure 2-4.

More specific data about the Bulkscanner including dimensions etcetera can be found in

Appendix D.

-

=

Figure 2-3 Working principle Bulkscanner

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6

2.6 Surface calculation algorithm

As described earlier the Bulkscanner receives a lot of coordinates. With these coordinates the

area needs to be calculated. The exact algorithm that is used to determine the area below the

Bulkscanner is not known. The company does not want to release this information. Possible

methods to determine the surface are described by F. Zeng et al (2015), and will be shortly

discussed in the following paragraphs.

2.6.1 Triangular surface calculation algorithm

The triangular surface calculation algorithm calculates the area by taking two adjacent points

registered by the Bulkscanner and the coordinate of the Bulkscanner itself. These 3

coordinates form a triangle, see Figure 2-5a. This triangle is extrapolated towards the

conveyor belt. The area of this triangle is calculated; this is done for all coordinates that are

measured. Summing up all these triangular areas will give the total area. Also, two shapes that

will be used in further research are shown and the area that this algorithm will measure is

showed in Figure 2-5b and Figure 2-5c. What can be seen is that this algorithm does not

predict sharp edges very well. A rectangular is an example of a shape with sharp edges. A

triangle, or an approximation of a triangle, can be better predicted by this algorithm.

2.6.2 Trapezoid surface calculation algorithm

The trapezoid algorithm uses a different algorithm to calculate the surface, but it also uses

coordinates. Again, the coordinates of two adjacent points are taken and between these

coordinates a linear line is fitted. With two vertical lines between these points and the belt a

trapezoid area can be formed. This is shown in Figure 2-6a. Again all areas are summed up to

calculate the total surface. For the two shapes that will be researched the area that will be

calculated with this algorithm is shown in Figure 2-6b and Figure 2-6c. As can be seen this

algorithm can better predict sharp edges. The total area that is calculated for the triangular

formed shape is approximately the same as when the triangular algorithm is used.

a)

b)

c)

Figure 2-5 Triangular surface calculation algorithm

a)

b)

c)

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7

2.6.3 Comparison of the two calculation algorithms

The difference between the two calculation algorithms can best be seen if Figure 2-5a is

compared with Figure 2-6a. The first algorithm calculates the area between two coordinates

by extrapolating the triangle formed by the coordinates and the origin of the laser. The second

algorithm assumes the area beneath the coordinates to be a rectangular and thus calculates the

area by assuming the bulk area to be trapezium shaped.

2.7 Specifications of the Bulkscanner

In Table 2-1 an overview is given of the relevant specifications of the Bulkscanner for this

research. They are derived from the operating instructions (Sick, 2012). The full operation

instructions can be found in Appendix D.

Feature

Minimum

Typical

Maximum

Angular resolution

-

0.5°

-

Scan frequency

35 Hz

50 Hz

75 Hz

Sensor-Bulk distance

0.5 m

-

10 m

Belt Speed

-30 m/s

-

30 m/s

Cycle time

13.3 ms

20 ms

28.6 ms

Measurement Accuracy

±5%

-

±3%

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8

3 Designing the experimental

setups

In this chapter the experimental designs are discussed. First the requirements for the

experimental setups are given. Then the rough principles of the designs are given. These

designs are discussed separately and improved if necessary until the experimental setups are

accurate enough for the real experiments.

3.1 Requirements for the experimental setup

Before an experimental setup can be designed it is necessary to know what results are

expected from the setup. In this case the laboratory setup should help determine the accuracy

of the Bulkscanner and the influence of several parameters on its accuracy. Therefore the

setup should be designed in such a way that the following parameters can easily and

accurately be changed during the research:

• Position of the Bulkscanner

• Dimensions and shape/type of the bulk material

• Background colour

• Belt speed

All other influences should be minimized. On a conveyor belt there are a lot of variables that

have an effect on the output. Amongst these are the vibrations of the system, the belt sag, and

the accuracy of the speed of the conveyor belt.

To make sure that these variables do not have an effect on the results of the experiment, two

different experimental setups will be used. The first setup will be without a conveyor belt and

the second setup will include a conveyor belt. From now on these two setups will be called

Static and Dynamic. These two setups are systematically shown in Figure 3-1.

At the static setup all variables except the belt speed can be researched. The results from the

static experiments will help to determine the parameters for the dynamic setup. In the next

paragraphs both setups will be separately discussed. Pre experiments will be conducted to see

if the setup is accurate enough or if improvements are necessary.

a) Static, at standstill

b) Dynamic, at the conveyor belt

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3.2 Design of the static setup

In this paragraph the design principle for the static setup, as shown in in Figure 3-1a will be

worked out into detail. First the material that is going to be measured is discussed. Then a first

proposal for the setup is given. This setup is build and the data of the Bulkscanner is analysed.

This data will be used to improve the setup until the results are satisfactory.

3.2.1 Materials to be measured with the static setup

The material that has been chosen for the static setup is Duplo. The reason is that the

dimensions of Duplo are really accurate and that it is easy to build different shapes out of

Duplo. When using a ground plate it is also easy to accurately place the blocks in the setup.

This makes it easy to perform multiple experiments. As an example, Duplo bricks are shown

in Figure 3-2.

The actual tolerances of Duplo bricks are hard to find. However, for Lego, other blocks made

by the same company, the tolerances are known. Because Duplo bricks are exactly twice as

big as Lego bricks, and the system that is used to assemble the bricks is also the same, it is

assumed that the tolerance is also twice as big as for Lego bricks.

For Lego bricks it is known that the tolerance is 0.1 mm (Cailliau, 2009). Lego bricks are

designed in such a way that for a perfect brick the gap between two bricks should be 0.1 mm.

This makes sure that two Lego bricks will always fit together.

This means that Duplo will have an accuracy of 0.2 mm. For the smallest measured area in

this research, consisting of a Duplo brick with dimensions 63.5 mm by 31.7 mm this means

that the area can at maximum deviate 0.47 %.

Because the bricks are placed on a ground plate, every brick on itself will be positioned with

this accuracy. In other words if a row of bricks is placed on the ground plate the maximum

deviation in length for the whole row is still 0.2mm. This means that for shapes built of

multiple bricks the accuracy is even higher. For a triangular shape, which is used in almost all

researches, the area created by the Duplo bricks can deviate 0.18% at most.

Because of the high accuracy, the average area of the Duplo bricks will be used as the real

area and the measured area will be compared with the average area.

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3.2.2 First proposed static setup

The first static setup can be seen Figure 3-3. The setup consists of the Bulkscanner LMS-511,

a computer, a black plate, Duplo and a Duplo ground plate. The Bulkscanner was placed on

the ground, in front of the black plate. The distance to the bulk was measured with a

measuring tape. The Bulkscanner type LMS511 is connected to a computer using a LAN

cable. The software package SOPAS engineering tool version 3.1.4 (Sick.com, 2015) is used

to extract the data from the sensor. The six rectangular shapes shown in Figure 3-3 were

measured. The shapes are shown in a top view.

Figure 3-4 shows the results of these tests. The numbers at the bottom are the percentages that

the average of the measured area differs from the real area. A negative percentage means that

the Bulkscanner underestimates the real area. A positive sign stands for an overestimation of

the real area. The data from the Bulkscanner is shown with a boxplot. The average value is

shown in red and the blue box gives the 25

th

percentiles. The black lines represent the 75

th

percentile. The outliers are also plotted in red. This holds for all graphs in this report. For the

data approximately 10000 data samples were analysed. The Real area is calculated by

multiplying the area of one Duplo brick by the amount of Duplo bricks used in the tests. The

used Matlab script is given in Appendix A. The used excel files to specify the amount of

Duplo brick used in a test can be found on the CD in Appendix C.

Figure 3-3 First experimental setup

Test 1 -7.1% Test 2 -18.2% Test 3 -44.1% Test 4 -10.4% Test 5 -26.4% Test 6 -63.3% Testnumber [-] and percentage that the Bulkscanner measurement differs from the real area 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 Area [m 2]

Average Measured area Real area

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11 This plot already shows some interesting results. It shows that for experiment 1 through 3 and

4 through 6 holds, that the further the blocks are placed to the back, the bigger the percentage

error is. This could mean that smaller areas are harder to measure for the Bulkscanner. It also

shows that test 4 is more accurate than test 3, even though the area is the same.

Because of the high difference in the measured area and the real area this setup needed

improvement. The graph shows that the results are better for bigger shapes. To improve the

setup the shapes that will be measured will be made bigger. Another possible improvement is

to fix the ground plate to the ground and to use the wall as a background instead of a loose

plate to ensure no errors could occur due to slight movements during experiments.

3.2.3 Second proposed static setup

In this setup the ground plate was fixed to the ground and placed in front of a wall. Another

improvement was that the position of the Bulkscanner was made visible by using tape on the

ground. This made it easier to bring the Bulkscanner into position for further tests. The setup

is shown in Figure 3-5.

The results are shown in Figure 3-6.

Figure 3-5 Second experimental setup

Test 1 17% Test 2 7.6% Test 3 -2.9% Test 4 19% Test 5 9.6% Test 6 2.2%

Testnumber [-] and percentage that the Bulkscanner measurement differs from the real area

0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 Area [m 2 ]

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12 The accuracy of these results are better then those of the first setup. In contrary to the first

setup, the bigger the area is, the less accurate the results are. To find out what causes these

differences, it is useful to know how the Bulkscanner calculates the area. Because the

company did not want to give information about the algorithm, the first parameter to be

researched will be the influence of the shape of the material. Possible algorithms were

discussed earlier in paragraph 2.6.

In this proposed experiment two measurements have a higher accuracy then the minimum

accuracy specified by the manufacturer as given in Table 2-1. This proves that this setup is

able to measure the area of the material in an acceptable way. Therefore this setup will be

used for the experiments.

3.3 Design of the dynamic setup

In this paragraph the design principle for the dynamic setup, as shown in in Figure 3-1b will

be worked out into detail. First the material that is going to be measured is discussed. Then a

first proposal for the setup is given. This setup is build and the data of the Bulkscanner is

analysed. This data will be used to improve the setup until the results are satisfactory.

3.3.1 Materials to be measured with the dynamic setup

Because in reality the Bulkscanner is used to measure bulk material, real bulk material will be

used. The disadvantage with real bulk material is that the cross sectional surface is not known.

However, the total volume that will be measured can be known by calculating it before

experimenting. Therefore, it is possible to use bulk material to test the feasibility of the

Bulkscanner. The bulk materials that will be tested are Dorsilit and wood pellets. Both

materials are depicted in Figure 3-7. They are chosen because their characteristics are very

different and it is thus interesting to compare the results.

To measure the volume of the bulk material, a bucket was completely filled with water. The

bucket was weighed and then the weight of the bucket itself was subtracted. By dividing the

weight of the water by the density of water the volume was calculated. It is hard to determine

the accuracy of this method. Small errors can be made while calculating the bucket’s volume.

Also, a person is not capable of exactly filling the whole bucket, and therefore small errors

will occur. Because no information is available about the accuracy, the measured volume will

be used as the real volume. In future research it is recommended to use a method with a

known accuracy. Another problem with this method is that shaking the bucket will increase

a) Dorsilit

b) Wood pellets

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13 the Bulk density and thus too much material will be used for the experiment. This problem

was minimized by carefully filling the bucket without shaking it.

3.3.1.1 Dorsilit

Dorsilit is chosen because it is very fine sand and thus completely different bulk material then

the wood pellets. It is washed several times to ensure that it is free from contaminations. It has

a uniform and round grain (Eurogrit, 2014). The diameter of the Dorsilit used is between 0.1

and 0.5 mm.

3.3.1.2 Wood pellets

Wood pellets are a form of solid biomass. They are made from harvest residues from the

forest industry. Wood pallets consist of dried sawdust, wood shavings, and/or wood powder

(Lanphen, 2014). The wood pellets used were produced at EPM Moerdijk for Essent. The

diameter is 8 mm and the length ranges from 5 to

35 mm.

3.3.2 First proposed dynamic setup

The setup can be seen in Figure 3-8. The setup consists of the Bulkscanner LMS-511, a

computer, a frame to position the Bulkscanner above the conveyor belt which is constructed

out of wooden beams, a conveyor belt (Belt length 2200 mm, belt width 400mm), an engine

(Unidrive T71A2), and a frequency convertor (Schneider electric atv12h037m2). According

to the manual, the Bulkscanner should be positioned above an idler. Because the conveyor

belt that is used only had idlers at the beginning of the belt and the end of the belt this was not

possible. However, a frame supported the whole belt so belt sag was not an issue.

The Bulkscanner type LMS511 is connected to a computer using a LAN cable. The software

package SOPAS engineering tool version 3.1.4 (Sick.com, 2015) is used to extract the data

from the sensor.

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14 The stiffness of the frame was improved by adding cross members and attaching the frame to

the table with clamp tools. This ensured that the position of the Bulkscanner does not change

during the experiment.

The belt speed was calculated by marking the belt and the frame of the conveyor belt with a

marker. A few rotations were filmed and the time it took for the markings to cross each other

were derived from the film. Two tests were executed both with 5.85 liters of sand at a speed

of 0,2 m/s.

The results are shown in Figure 3-9. The graph looks similar to the graph from the static

experiment shown in 3.2.2. The differences are that the volume is on the y-axis instead of the

area. Furthermore the measured volume by the Bulkscanner is now one value instead of a

boxplot. This is because at the static setup the same area was measured. In the dynamic setup,

every sample gives a different area at a different time. All these areas are needed to calculate

the total volume. Equation (1) was used to calculate the volume. In Appendix B the Matlab

script that calculated the volume can be found.

! =

!

_!!!

− !

_!

∗ !

_!

∗ !

_!!"# !!!!! !!!

(1)

With:

V

Volume [m

3

]

s

Amount of samples [-]

t

n

time at certain sample[s]

A

n

Area at certain sample [m

2

]

V

belt

Belt speed [m/s]

In paragraph 3.3.1 is explained how the real volume is calculated.

Test 1 26.8% Test 2 23.6%

Testnumber [-] and percentage that the Bulkscanner measurement differs from the real Volume

0.009 0.0095 0.01 0.0105 0.011 0.0115 0.012 0.0125 0.013 0.0135 Volume [m 3] Measured Volume Real Volume

(24)

15 The results are not that accurate. One explanation could be that the belt speed is not calculated

accurately. It is also possible that the belt speed is not constant. Another possibility is that it is

hard to empty the bucket in such a way that the bulk material has an acceptable angle of

repose. The sand should thus not spread out much over the width of the conveyor belt but it

should remain some height. Furthermore every test only gives one volume in contrary to the

static tests where every test gave approximately 10000 measurements for the area. This also

makes the test less reliable.

3.3.3 Second proposed dynamic setup

To tackle the problem with determining the belt speed a Voltkraft DT-30LK tachometer, see

Figure 3-10a, was used to measure the speed of the belt. This made it easier to test the belt

speed during tests to ensure the right belt speed was used. Unfortunately this method showed

that the belt speed was not completely constant as assumed in the volume calculations. This is

probably due to the frequency convertor or the conveyor belt itself. A slight decrease of speed

occurred when the material was placed on the belt. This was however always less then 4%

when the complete bucket was placed on the conveyor belt. The actual speed deviation during

the experiment will thus be lower and acceptable.

The problem of getting the material in a proper way on the belt was partly solved by repeating

the experiment a couple of times. After some practice the right unloading speed was found

which gave the bulk material sufficient height, which can be seen in Figure 3-10b.

The results are shown in Figure 3-11. Again, both tests are conducted with Dorsilit sand and

with a conveyor belt speed of 0.2 m/s. The results differ less then 10 per cent from the real

volume. Because improving the setup further would requires a lot of research, and possibly

building a complete new setup it was not possible within the time span of this research. A

deviation in the measurement of the volume of less then 10 per cent will thus be seen as

acceptable.

a) Tachometer

b) bulk material on belt

(25)

16 To make sure that in every experiment the same steps are taken, the experimental steps were

documented. These can be found in chapter 4. To make sure all the graphs are the same and

no errors were made, two scripts were made to automatically generate the plots. The code can

be found in Appendix A and Appendix B.

Test 1 4.5% Test 2 8.6%

Testnumber [-] and percentage that the Bulkscanner measurement differs from the real Volume 5.4 5.6 5.8 6 6.2 6.4 6.6 6.8 Volume [m 3] ×10-3 Measured Volume Real Volume

(26)

17

4 Measurement steps

In this chapter all steps that need to be conducted for an experiment are explained so that in

future research the experiments can be repeated. First the user interface is explained.

4.1 User interface

When the program starts, the screen as showed in Figure 4-1a pops up. This is the main

screen, which shows the devices that are available. In this screenshot the Bulkscanner

LMS-511 is already imported in the project. In Appendix D can be read how to do this. The main

screen also gives access to the data recorder. This function can be used to export data

recorded by the scanner. In Figure 4-1b the settings of the data recorder are shown. The

record interval, maximum record time, output location, file type, and the data to be recorded

can be set. If the Bulkscanner is selected, a new screen opens that shows the view of the

scanner. This screen in shown in Figure 4-1c. In this screen the output of the scanner can be

visually monitored. Setting up the scanner is also done in this screen. At the tab teach-in the

device can be learned where the conveyor belt is and the bandwidth can be set. If the tab

system parameters is selected, see Figure 4-1d more settings like tolerances and a fixed belt

speed can be set.

c) Scanner view

d) System parameters tab

Figure 4-1 Screenshots of Sopas engineering software

(27)

18

4.2 Static: Measurement steps

The following steps were taken for every static experiment:

• Put the Bulkscanner in the right position;

• open Sopas, press project, login as ‘service client’, password ‘client’ (see Figure

4-1a);

• click on the Bulkscanner image to open the scan view;

• put the device in ‘maintenance mode’ (see Figure 4-1c);

• make sure that the ‘fixed belt speed’ is set to one [m/s] (see Figure 4-1d);

• put Duplo Bricks at the side of the ground plate and change the angle of the device

in such a way that it measures the whole ground plate including the placed bricks;

• set the ‘device radius’ in such a way that it can measure the wall and the bulk

material (see Figure 4-1c);

• remove the Duplo bricks;

• press ‘teach-in’;

• set the device to ‘measuring mode’;

• place the Bulk material on the ground plate;

• go to ‘data recorder’ (see Figure 4-1a);

• press on the gear wheel symbol to open the data recorder settings;

• set the recorder to measure every 10 [ms] for 30 [s] (see Figure 4-1b);

• make sure ‘Volumeflow’ is selected as output value;

• set the filename to the number of the test and the file type to .xlsx;

• make sure all the right parameters are set in the excel file that contains information

about the setup;

(28)

19

4.3 Dynamic: Measurement steps

The following steps were taken for every dynamic experiment:

• Put the Bulkscanner at the right height;

• open Sopas, press project, login as ‘service client’, password ‘client’ (see Figure

4-1a);

• click on the Bulkscanner image to open the scan view;

• put the device in ‘maintenance mode’(see Figure 4-1c);

• make sure that the fixed belt speed is set to 1 [m/s] (the right Bulk speed is listed

in de excel file that contains all the information about the tests; Matlab uses this

speed to calculate the volume) (see Figure 4-1d);

• put some material on both sides of the conveyor belt and change the angle of the

device in such a way that it measures the whole conveyor belt;

• set the ‘device radius’ in such a way that it can measure the conveyor belt and the

bulk material (see Figure 4-1c);

• remove the material;

• press ‘teach in’;

• set the device to ‘measuring mode’;

• fill the bucket with Bulk material and place it in front of the conveyor belt;

• set the frequency of the belt to a value corresponding with the right conveyor

speed and check the speed using the speed sensor;

• go to data recorder (see Figure 4-1a);

• press on the gear wheel symbol to open the data recorder settings;

• set the recorder to measure every 10 [ms] for an unlimited time (see Figure 4-1b);

• make sure ‘Volumeflow’ is selected as output value;

• set the filename to the number of the test and the file type to .xlsx;

• make sure all the right parameters are set in the excel file that contains information

like the Bulk Volume, type and belt speed;

• lift up the bucket;

• press ‘record’(see Figure 4-1a);

• pour the bulk material on the belt;

(29)

20

5 Experiments

This chapter will discuss all experiments to be conducted for the static setups and the dynamic

setups. In chapter 5.1 all static experiments that have to be conducted are discussed. In

chapter 5.2 al dynamic experiments that have to be conducted are discussed.

5.1 Static experiments

In chapter 3.1 the parameters to be researched are stated. The following parameters will be

tested in the static setup and will be discussed in the following sub paragraphs:

• Dimensions and shape of the bulk material

• Position of the Bulkscanner

• Background colour

5.1.1 Static: dimensions and shape of the bulk material

To determine the influence of the dimensions and shape of the bulk material, the shapes that

will be measured are shown in Figure 5-1. Dimensions are taken into account because testing

the experimental setup showed that the bulk dimensions have an influence on the accuracy.

Because the measurement principle is unknown, but a triangular shaped material gives best

results for the found possible algorithms, as explained in 2.6.1 and 2.6.2 this shape will also

be measured. Because the material is build up using Duplo bricks, a real triangle is quite hard

to build. Therefore, the shape as shown in Figure 5-1 at the right is chosen. For all further

setups the shape that has the highest accuracy will be used.

5.1.2 Static: position of the Bulkscanner

The second variable to be researched is the position of the Bulkscanner. In Figure 5-2 a

systematic overview of the different positions of the Bulkscanner is shown.

The Bulkscanner can measure bulk if the distance between the bulk and the scanner is

between half a meter and 10 meter (Sick, 2012). The Bulkscanner will determine the area by

Figure 5-2 Position of the Bulkscanner

Figure 5-1 Bulk shapes to determine the influence of

material dimensions and shape

(30)

21 evaluating all the data points that give information about the contour of the bulk. Because the

angular resolution of the Bulkscanner is 0.5 degrees, it is expected that the closer the

Bulkscanner is to the bulk material, the more accurate it is. Therefore, the distances that are

tested will start from the minimum distance of 0.5 meter. All distances tested, and the test

numbers are given in Table 5-1.

Testnumber [-]

Distance Bukscanner to Bulk [m]

1

0.5

2

0.75

3

1

4

1.25 Table 5-1 Test number and corresponding distance to Bulkscanner

For all further setups the best position for the Bulkscanner is used.

5.1.3 Static: background colour

Another parameter which needs to be tested is the colour of the background. Both black and

white will be tested to see the difference between a surface that reflects or absorbs light. To

achieve this black and white paper are respectively placed in front of the wall. Blue is also

tested because the wall itself is blue. Aluminium foil is also tested in order to see if a material

that reflects normal light in different angles will also influence laser beams. An overview is

given in Table 5-2.

Test no. [-]

Distance Bukscanner to Bulk [m]

1 Blue (wall colour)

2 White (paper)

3 Black (paper)

4 Reflecting (Aluminiumfoil)

Table 5-2 Test number and corresponding background colour

5.2 Dynamic experiments

In chapter 3.1 the parameters to be researched are stated. The following parameters will be

tested in the dynamic setup and will be discussed in the following sub paragraphs:

• Type of bulk material

• Position of the Bulkscanner

• Belt speed

5.2.1 Dynamic: bulk material type

The first parameter that will be tested for this setup is the material type. Both Dorsilit and

Wood pellets, earlier described in 3.3.1, are tested. All other variables, like the belt speed and

the height of the Bulkscanner are kept constant. In this setup, it is not easy to change the

height of the Bulkscanner. Furthermore, the height of the bulk is not constant during an

experiment. Therefore, the height is now defined as the distance to the belt instead of the bulk

material. The smallest distance is 0.7 meter because the bulk height will never be higher then

0.2 m. This ensures that the minimum bulk distance is always larger then 0.5 m. An overview

of all the values is given in Table 5-3.

(31)

22 Test no. [-] Amount tests [-]

Material [-] Speed [m/s] Bulkscanner height [m]

1

4 Pellets

0.1

0.7

2

3 Dorsilit

0.1

0.7 Table 5-3 Test number and corresponding parameter values for testing the material type

5.2.2 Dynamic: Position of the Bulkscanner

Because the setup could not be too high due to stability reasons, only two heights will be

tested. During these tests the material and belt speed will be kept constant, as can be seen in

Table 5-4.

Test no. [-] Amount tests [-]

Material [-] Speed [m/s] Bulkscanner height [m]

1

4 Dorsilit

0.1

0.7

2

4 Dorsilit

0.1

0.95 Table 5-4 Test number and corresponding parameter values for testing the Bulkscanner height

5.2.3 Dynamic: conveyor belt speed

Finally, the belt speed will be investigated. Three speeds will be tested; 0.1, 0.2 and 0.3 m/s.

These speeds were chosen because they are not so slow that adding bulk material to the belt

will reduce the speed drastically and they are not so fast that there will be a lot of dust. Again,

all other parameters are kept constant, as can be seen in Table 5-5.

Test no. [-] Amount tests [-]

Material [-] Speed [m/s] Bulkscanner height [m]

1

4 Dorsilit

0.1

0.7

2

5 Dorsilit

0.2

0.7

3

6 Dorsilit

0.3

0.7

(32)

23

6 Results

In this chapter the results from all the experiments will be presented. All the setups as

described in chapter 5 will be discussed separately in the next paragraphs. The results will

also be discussed and possible causes for certain outcomes are given.

6.1 Static results

In this chapter all results from the static tests that are described in paragraph 5.1 are given.

6.1.1 Static: Dimensions and shape of the bulk material

First, the different tests are shown again in Figure 6-1. The percentage the measured area

differs from the real area is also shown.

The results depicted in Figure 6-2 show that there is no significant difference between the two

rectangular shapes in test 1 and 2. The triangular shape in test 3 however, does show a

significant difference. The average of the measured data by the Bulkscanner underestimates

the area with only 4.8 per cent.

a) 20.6%* b) 19.8%* c) -4.8%*

* Percentage that the Bulkscanner measurement differs from the real area

Figure 6-1 Bulk shapes to determine the influence of material dimensions and shape

Test 1 20.6% Test 2 19.8% Test 3 -4.8% Testnumber [-] and percentage that the Bulkscanner measurement differs from the real area 0.04 0.05 0.06 0.07 0.08 0.09 Area [m 2]

(33)

24 The big differences are likely caused by the way the Bulkscanner measures an area. Sharp

edges, like rectangular shapes, are not that well predicted. A possible explanation for the error

in measuring objects with sharp edges is depicted in Figure 6-3. Possibly, the scanner also

counts the two blue triangles left and right of the object as area. This explains the

overestimation of the area.

To test this hypothesis the results are plotted again. Now the area with the two triangles is

calculated and plotted, see Figure 6-4. The plot shows that the measured area is between the

real area and the possible measurement algorithm that was suggested.

From now on the triangular shape from test 3 will be used to test the influence of other

parameters.

Figure 6-3 Bulkscanner

measuring a rectangular shape

Test 1 20.6% Test 2 19.8% Test 3 -4.8% Testnumber [-] and percentage that the Bulkscanner measurement differs from the real area 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.13 Area [m 2]

Possible measurement algorithm

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25

6.1.2 Static: Position of the Bulkscanner

As a reminder, the different tests are shown again in Table 6-1. The percentage the measured

area differs from the real area is also shown.

Testnumber [-] Distance Bukscanner

to Bulk [m]

Percentage difference between

measured area and real area [%]

1

0.5 -4.8

2

0.75 -3.1

3

1 -4.9

4

1.25 -6.2

Table 6-1 Test number and corresponding distance to Bulkscanner

In Figure 6-5 the results for the positions of the Bulkscanner are shown. It can be seen that the

best results are obtained at a distance of 0.75 meters. Longer distances will reduce the

accuracy. Furthermore placing the Bulkscanner closer to the bulk, at 0.5 meters, will also

reduce the accuracy. This is remarkable because it was expected that the closer the

Bulkscanner was to the bulk material the better the results.

An explanation for this phenomenon can be that the distance of 0.5 meter is on the edge of the

working domain of the Bulkscanner and therefore its results are worse. Another explanation

can be that there were systematic errors in the setup. These errors could be the cause of a

lower accuracy at 0.5 Meters.

Test 1 -4.8% Test 2 -3.1% Test 3 -4.9% Test 4 -6.2% Testnumber [-] and percentage that the Bulkscanner measurement differs from the real area 0.038 0.04 0.042 0.044 0.046 0.048 Area [m 2]

(35)

26

6.1.3 Static: Background colour

First, the different tests are shown again in Table 6-2. The percentage the measured area

differs from the real area is also shown.

Testnumber [-] Distance Bukscanner to Bulk

[m]

Percentage difference between

measured area and real area [%]

1 Blue (wall colour)

-3.1

2 White (paper)

-5.6

3 Black (paper)

-3.3

4 Reflecting (Aluminiumfoil)

-6.3

Table 6-2 Test number and corresponding background colour

The results are given in Figure 6-6. What can be seen is that the dark colours, like black and

dark blue, gave the best results. White and aluminium paper gave worse results.

The colours black and white were both realised by putting a sheet of paper behind the setup.

Putting a sheet of paper behind the Bulkscanner could influence the measurements. However,

it can be reasonably assumed that this is not the case due to the positive results with black

paper. Therefore, it is assumed that the worse accuracy for the white paper is not due to the

paper’s thickness that was added to the setup.

For aluminium foil the worse accuracy can be due to a less accurate experimental setup. In

contrary to paper, the aluminium foil was not completely flat which can result in some errors.

The difference in accuracy of more then 3 per cent is probably not only because of the

rougher surface. The fact that aluminium foil reflects light in different angles will most likely

be the cause of the Bulk scanner’s inaccuracy.

Test 1 -3.1% Test 2 -5.6% Test 3 -3.3% Test 4 -6.3% Testnumber [-] and percentage that the Bulkscanner measurement differs from the real area 0.038 0.04 0.042 0.044 0.046 0.048 Area [m 2 ]

(36)

27

6.1.4 Static: conclusions.

From the static experiments can be concluded that for this particular setup a triangular shape

can best be measured. The results are way more accurate than measurements with rectangular

shapes. This is probably because of the algorithm used by the Bulkscanner to calculate the

area. Unfortunately the algorithm used could not be derived.

The best distance of the Bulkscanner to the bulk material for this setup was 0.75 meters. This

was not the lowest tested distance within the bandwidth specified by the company. Probably

the measurement at 0.5 m was worse because is the minimum distance specified by the

manufacturer. The closer the device the more data points it generates on the surface of the

bulk and thus results were better at 0.75 meters then at bigger distances.

Also was shown that dark colours work best as a background colour. The best result was

obtained with a blue background. A black background gave almost the same result. Because

the boxplots overlap it is not possible to tell which colour is better.

6.2 Dynamic results

In this chapter all results from the static tests that are described in paragraph 5.2 are given.

6.2.1 Dynamic: Bulk material type

An overview of the two tests that were executed is shown in table Table 6-3. The percentage

the measured area differs from the real area is also shown. The two types of bulk material, as

discussed in paragraph 3.3.1, were tested. For the speed, the slowest option where the belt

speed was still relatively constant when bulk was poured on the belt was chosen. For the

Bulkscanner height the lowest height was chosen.

Test

no. [-]

Amount

tests [-]

Materi

al [-]

Speed

[m/s]

Bulkscanner

height [m]

Percentage difference between

measured area and real area [%]

1

4 Dorsilit 0.1

0.7

3.9

2

3 Pellets

0.1

0.7 -10.7

Table 6-3 Test number and corresponding parameter values for testing the material type

The results of the tests are depicted in Figure 6-7.

Test 1 3.9% Test 2 -10.7%

Testnumber [-] and percentage that the Bulkscanner measurement differs from the real volume

4.8 5 5.2 5.4 5.6 5.8 6 6.2 6.4 6.6 Volume [m 3] ×10-3 Measured Volume Real Volume