Process simulation for Rose grading, sorting and packing - Simulatie van het beoordelen, sorteren en verpakken van rozen

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Delft University of Technology

FACULTY MECHANICAL, MARITIME AND MATERIALS ENGINEERING

Department Maritime 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 26 pages and 1 appendix. 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.

i Specialization: Transport Engineering and Logistics

Report number: 2016.TEL.8055

Title: Process simulation for Rose grading, sorting and packing.

Author: W. Vreugdenhil

Simulatie van het beoordelen, sorteren en verpakken van rozen.

Assignment: internship Confidential: yes

Initiator (university): dr.ir. Y. Pang Initiator (company): Ing. Kees Bukman External supervisor: Dr. ir. Wouter Bac Internal supervisor: Dr. ir. Y.Pang

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Summary

In many rose cultivation greenhouses a sorting and packing machine of the company AWETA is used. This machine consists of out of classification with the use of pictures and vision, a sorting machine with many exits, each exit has its own bunch station where roses are bundled, followed by a belt system which transports the bunches to sealers. Due to a new camera, vision and classification system the quality of the roses can be determined more precise and more quality classes can be distinguished. This results in uneven use of the exits of the sorting machine. Thereby some parts of the machine are used more intensively and others are used less intensively.

Some bunch stations cannot handle the amount of roses offered and have to reject the roses. This will result in roses which are downgraded in some greenhouses. In other greenhouses there occurs a capacity reduction of the machine due to this phenomenon. Both the effects are undesirable.

To reduce this problem some parts of the machine could be improved. First the parts and bottlenecks which cause the problem has to be identified. Besides the amount of roses rejected per cause must be determined.

There is a lack of insight in the bottlenecks of the machine. This insight is provided by a discrete event simulation of the reality. Therefore data about the amount of roses Offered, Accepted and rejected and data about the timing of the machine is collected.

With the use of this data the simulation is constructed and validated. The result of the simulation gives an overview of the amount of roses rejected per cause per bunch station. It can be seen that the amount of roses rejected differ a lot per cause. About 50%, the largest part, of the roses which are rejected, are rejected because of the fork change within a bunch station. Another remarkable result is an outlier at bunch station 8.

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iii

Assignment description

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content

Summary ...ii

Assignment description ... iii

1. Introduction ... 2

1.1. Objective... 2

1.2. Research questions... 3

1.3. Approach ... 3

1.4. Outline of report... 4

2. Process description of harvesting, sorting and packing roses ... 5

2.1. Process steps ... 5

2.2. System boundaries ... 10

3. Data from the reality ... 11

3.1. Data sets ... 11

3.2. Deviations and incompleteness ... 11

3.3. Data processing ... 12

3.4. Timing data ... 13

4. Simulation model ... 16

4.1. Situation to be modelled ... 16

4.2. Simulation model construction ... 16

4.3. Result 1, amount of offered accepted and rejected roses ... 17

4.4. Result 2, rejected roses per bunch station per reason of rejection ... 18

5. Model validations ... 20

5.1. Verification with available data ... 20

5.2. Verification of bunch station with video ... 21

5.3. Validation of v-belt with video ... 21

6. Conclusion ... 24

6.1. Answers to research questions ... 24

Recommendations ... 25

Bibliography ... 26

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1. Introduction

In rose cultivation companies, roses are grown, harvested and sorted. The price a rose is sold for is dependent on the quality of the rose, which is determined by the characteristics of the rose. The roses must be sorted to be able to sell bunches of roses which contain same-looking roses. Many companies in the Netherlands use a AWETA sorting and packing machine as depicted in Figure 1-1. This machine photographs all the roses and analyses the characteristics of the roses with image processing. Characteristics to be determined are the stem length, stem width, and bud size, ripeness and colour. When the properties of the roses are determined the roses will be classified in a certain category.

The company “4More technology” has developed and new camera and image processing system which is called “IRISS” (Intilligent Rozen Inspectie- en Sorteer Systeem). With IRISS more characteristics of the roses can be determined and the characteristics can be determined more precisely. The characteristics IRISS can measure are: stem length, stem with, stem bend, bud height, bud width, bud colour, neck angle, ripeness and damage (Figure 2-5). An additional advantage is that less manual inspection of the harvested roses to detect defects is necessary.

Because of this progress in determining the characteristics of the roses, more quality classes can be distinguished which will result in higher profit for the greenhouses. However the amount of quality classes is limited by the amount of outputs of the sorting machine. Another consequence of having more quality classes is that the different parts of the sorting machine are used less equally and thereby a higher performance of a number of parts of the sorting machine is desired. In the current situation there are some limitations in the machine. As a result of these limitations some roses are sorted in a too low quality class and some roses aren’t sorted at all. These roses has to be processed for a second time. Unfortunately, there is no direct insight into the causes of limitations and bottlenecks. This information could be achieved with a detailed simulation.

1.1. Objective

The objective is to have more insight in factors which influence the throughput of the entire machine and separate bunch stations. This insight could be provided with a simulation model of the current situation where certain factors and or settings can be modified easily to determine the effect of certain modifications.

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1.2. Research questions

The goal of the simulation model is to identify restrictions for the throughput. Using this information possible and relevant improvements can be defined. The main research question is:

- Which factors should be improved to enlarge the trough put of the entire machine or parts of the machine?

This question is answered with the following sub-questions. - How many roses are currently downgraded?

- What are the possible causes for rejecting roses at a bunch station?

- How many roses are rejected for each separate cause?

1.3. Approach

To get more insight in the sorting and packing machine and answer the research question, a simulation of the process is made. The first step for this simulation is to collect data from the reality. The available data concerning the amount of roses offered, accepted and rejected in reality originates from three different sources and has to be compared and processed firstly to have a dataset to use as a verification for the simulation. On the basis of these datasets also the amount of roses which are degraded has to be determined. Besides the data of the roses offered, accepted and rejected, data has to be collected about the timing of certain actions in the system.

Because the system can be decomposed in many little actions which follow one another or are dependent each other, this could be simulated very well with a discrete event simulation. A discrete event simulation makes use of queueing theory (Cassandras & Lafortune, 2010). This simulation will be constructed with SimEvents, which is a part of Simulink and Matlab.

At first the current situation of “Kwekerij Rozenhof b.v.” will be simulated. the simulation will be validated with two different methods. The first method is to compare the data from the reality and the simulation. For the second method videos of the reality are made which could be compared to the behaviour of the simulation.

When the simulation is considered to work properly, causes of rejecting roses will be extracted from the simulation. On the basis of these causes it can be determined which factors should be improved to enlarge the throughput of the machine.

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1.4. Outline of report

The general logistic process in the greenhouse from cutting a rose until packing bunches of roses into a bucket is described in Chapter 0. Chapter 3 gives an overview of all the data collected from the reality. Varying from data about the timing of certain process steps to data of offered, accepted and rejected roses. The construction of the simulation model is discussed in chapter 4, and the simulation validation is displayed in chapter 5. Conclusions and answers to the research questions are discussed in chapter 6.

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2. Process description of harvesting, sorting and packing roses

To understand the process of harvesting sorting and packing roses all the sub processes are discussed in this chapter. Thereafter the system boundaries for this research is delimited.

2.1. Process steps

A schematic overview of all the steps is shown in Figure 2-1. All the steps are briefly explained in this section.

Mobile cultivation system

In this greenhouse the available space to grow roses is used very efficiently. No space is wasted on side paths to be able to walk in-between the rose plants. Instead of walking through paths to cut the roses, a mobile cultivation system is used. The rose plants are placed on tables which move through the greenhouse. When a table is next to the main path, the roses which are ripe enough are harvested by employees of the greenhouse.

Harvesting roses

The stem of the rose is cut as low as possible. The stem length is an important factor for the quality and has a large influence on the value of the rose.

Mobile cultivation system harvest transport system transfer to sorting machine manual inspection photograph and classify transfer to

bunch station make bunches transfer to belt

collect enough bunches on belt tranfer to v-belt sealer transfer to

bucket to cart storage Figure 2-1 Process overview of harvesting, sorting and packing roses

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Transport system

When a rose is cut, it is attached to a fork, which is mounted on a rail (Figure 2-2). Each rail contains thirteen forks. When a rail is filled, it is transported automatically to the sorting machine. At the sorting machine there is a continuous flow of rails. Most of them are entirely filled with roses, but there may be some empty rails in between.

Transfer to sorting machine

When the rails arrive at the sorting machine the roses are transferred from the forks of the transport system to the forks of the sorting machine automatically (Figure 2-3).

Figure 2-3 Transfer to sorting machine

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Manual inspection

Before classifying the roses automatically, there is the possibility to mark a defect rose manually. On each fork there is a switch through which the rose could be given a manual inspection code. Two different defects can be assigned for each rose. The roses which couldn’t be processed by the machine are thrown out at the end of the machine. These roses are manually attached to empty forks for a second time at the location of the manual inspection (Figure 2-4).

Photographing and classifying roses

The stem and bud of each rose is photographed three times. With image processing the characteristics of the rose is determined. The characteristics which are determined are depicted in Figure 2-5. Besides the characteristics displayed in Figure 2-5 also the maturity, leaf structure and damage are measured. On the basis of these characteristics and the requirements of the quality classes the roses are classified.

Transfer to bunch station

The roses in the sorting machine move along all the bunch stations. Each quality class is assigned to one or more bunch station. In this way the sorting machine is able to send each rose has to the right bunch station. Unfortunately a bunch station can’t accept all the roses which are offered to that station. This has two causes, the first cause is that a bunch station has certain proceedings (discussed in the next section) during which the bunch station is not available to accept roses. The second cause is that the bunch station is full and can’t be emptied for a certain amount of time due to waiting times further on. When a certain quality class contains many roses, more than one bunch station is assigned to that quality class to be able to accept most of the roses. Another option is to send roses which couldn’t be accepted by a bunch station to a bunch station with a lower quality class. However, this causes a decrease of the value and has to be avoided when possible. All the roses which are not accepted by any bunch station will be thrown out at the end of the machine. Those roses will be put in the sorting machine again, but this time this is done by hand and therefore increases labour costs..

Figure 2-5 Rose characteristics Figure 2-4

a) Manual inspection

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Making bunches

In the bunch station single roses are processed to bunches of roses. When the roses are transferred from the sorting machine to the bunch station they arrive on a larger fork which can contain maximum four roses (Figure 2-6). When this fork is full, a new empty fork is set. During this fork change no roses can be accepted. When the amount of roses of one bunch, which is mostly ten, are arrived in the bunch station, the stems of the roses are pushed together and a string is put around the stems. During a part of this process no roses can be accepted to the bunch station.

Transfer to belt

When the bunch station is full, the stems are all cut to the same length, thereafter a mechanical arm grabs the bunch and drops it on a belt conveyor. During a part of the mechanical arm process, there can’t be a fork change. When the belt is already full, the arm with the bunch will wait until there is enough place to drop be bunch.

Buffer bunches on belt

The end product is one bucket of bunches. For different quality classes a different amount of bunches is sold per bucket. This varies from four to six bunches. The amount of bunches for one bucket is collected on a belt (Figure 2-7). Each bunch station has its own belt to collect bunches on. When there are enough bunches the belt will be emptied onto a v-belt conveyor as soon as there is enough space on the v-belt. When it is not possible to empty the belt conveyor, the belt stays full and no extra bunch can be dropped on the belt. This can also cause a stop of accepting roses for the accessory bunch station.

Figure 2-6 Bunch station in operation

Roses in sorting machine Fork being filled

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9 The belt consists out of one small belt and one larger belt. The smaller belt acts as a buffer. When the big belt is being emptied on the v-belt, one or two bunches can already be dropped on the small buffer belt.

Transfer to v-belt

Because the belts waits untill there are enought bunches for one bucket, always the right amount of bunches for one bucket will lay after each other on the v-belt. Bunchstations 1-7 have one v-belt and sealear, and bunchstation 8-14 have one v-belt and sealer.

V-belt transport

The v-belt moves with steps as big as the distance between the middles of two adjacent belts. The tact-time is determined by the speed of the sealer.

Sealer

The sealer puts a plastic packing around each bunch.

Transfer to bucket and cart

When the bunches are sealed, employees put the right amount of bunches in a bucket with a layer of water and put the buckets on a cart together with only buckets of that quality. The employees also do a last manual check for the right amount of roses in a bunch, all buds on the same height, defects and stem length.

Figure 2-7 overview rose sorting an packing machine

Belt

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Storage

When a cart is full, it is driven to the refrigerator where it is stored until it is transferred to, and transported by, a truck.

2.2. System boundaries

The processed described in section 2.1 is the process as situated in the greenhouse “Kwekerij Rozenhof b.v.”. In other rose cultivation greenhouses the situation will be largely the same, but there will also be crucial differences. This research is focussed to this specific greenhouse. In Figure 2-9 an overview of all the steps in the greenhouse from harvesting until packing are displayed. This research is delimited by the sorting and packing machine. The steps in this part are displayed in green, and the rest is displayed in blue.

Now the system boundaries are set and the steps within the system are known. The next step towards a simulation is to collect some data from the reality. The collection and processing of this data is discussed in the next chapter.

Figure 2-8 transfer to bucket and cart

Mobile cultivation

system

harvest transport _system

transfer to sorting machine manual inspection photograph and classify transfer to

bunch station make bunches transfer to belt

collect enough bunches on belt tranfer to v-belt sealer transfer to

bucket to cart storage Figure 2-9 Process overview of harvesting, sorting and packing roses

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3. Data from the reality

During the collecting of the data from reality there appeared to be three different sets of data concerning the roses which are processed. It was found that these datasets doesn’t always correspond with each other which appeared to have different causes.

At first the origins of the datasets are discussed, where after the deviations and incompleteness is explained. The data is processed and the right amount of roses accepted and rejected per bunch station is calculated and the amount of downgraded roses is calculated.

Besides the data of the roses, also data about the timing of certain actions is collected.

3.1. Data sets

The three possibilities to collect data are:

 AWETA: In the sorting machine (produced by AWETA) The amount of roses offered and Accepted per bunch station is stored. Only the total of the day until the current time is available and could be read from a screen.

 TRS Watch: This function is made later on and should store the amount of roses accepted and rejected pre bunch station every minute. The data is stored in the computer as a .csv file.  Roses sheet: In this sheet the characteristics of the roses resulting from the image processing

and the classification by IRISS is stored for each rose. The manual inspection code

determined by employees and whether a rose is if thrown out by the flipper or not, is also stored in this sheet.

3.2. Deviations and incompleteness

When the different data sets were compared a number of problems were discovered:

 If the sorting program is changed during the day, it is possible that (for instance) a quality class is assigned to another bunch station during the day. When this happens it is not certain anymore that a certain quality class, which can be seen in the Rose sheet, belongs to a certain bunch station, of which the data can be extracted from AWETA or TRS Watch.  If the software is updated during the day, for a few minutes the data of the roses which are

processed is not stored in the Rose sheet.

 TRS Watch stores the amount of roses offered and rejected every minute, so theoretical the last values of TRS Watch should match the day total of AWETA. Unfortunately this is not the case. The amount of roses in TRS watch is lower than in AWETA. However, for bunch stations which are not used very intensively the data of TRS watch and AWETA do often match. Because the total of the day in AWETA correspond to the Rose sheet, and the TRS watch doesn’t, AWETA is considered to be more reliable than TRS Watch.

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3.3. Data processing

To keep the simulation time relatively low the dataset used as verification for the simulation must not contain too much data. Therefore, there has been chosen to use the data from the start of a random workday until the first break. This results in Wednesday 11 may 05:45 AM until 08:49 AM. The bunch station settings are shown in

Table 3-1. In this table it can be seen that roses which are rejected at a station are sent trough to another station. For instance rose in quality class “60GROEN” are sent to station 4, when the roses are rejected at that station for some reason, they are passed on to station 10 followed by 11 and 12.

Table 3-1 Bunch station settings and amount of roses

From the roses sheet the amount of roses per quality class is counted and also shown in Table 3-1.

The amount of roses accepted per bunch station is extracted from AWETA and shown in Table 3-2. By using all the aforementioned information also the amount of roses offered and rejected per bunch station is calculated and also shown in Table 3-2.

Bunch

station 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Offered 545 2950 474 3936 1584 613 858 6783 75 2988 673 2188 1576 1492

Accepted 511 2596 443 3283 1357 532 783 4448 72 2315 517 1656 1303 1297

rejected 34 354 31 653 227 81 75 2335 3 673 156 532 273 195

Table 3-2 amount of roses per bunch station

In

Table 3-1 it can be seen that some roses are sent to a lower quality class if the bunch station in the first column is not able to accept the roses, which causes a loss in value. In Table 3-3 the amount of roses in each quality class are depicted per row and the quality class where the roses eventually end up are depicted per column. The roses which are downgraded are depicted in red.

Quality class Bunch station Amount of roses

40 16 0 0 0 300 50Normaal 14 16 0 0 1311 55Normaal 13 14 0 0 1111 60GROEN 4 10 11 12 3936 70Normaal 2 6 0 0 2950 80Normaal 1 6 0 0 518 90Normaal 1 0 0 0 27 60IRISS 7 9 0 0 827 70IRISS 3 7 9 0 474 60Brullers 15 0 0 0 107 55GROEN 12 13 0 0 2032 60NormSmal 8 10 11 12 6783 70GROEN 5 6 0 0 1584

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13 9 0N o rmaa l 8 0N o rmaa l 7 0I R IS S 7 0G ROE N 7 0N o rmaa l 6 0B ru lle rs 6 0I R IS S 6 0G ROE N 6 0N o rm Sma l 5 5G ROE N 5 5N o rmaa l 5 0N o rmaa l 40 90Normaal 0 25 80Normaal 486 30 70IRISS 443 31 70GROEN 1357 202 70Normaal 2896 60Brullers 104 60IRISS 824 60GROEN 3283 619 27 60NormSmal 6661 62 55GROEN 1567 373 55Normaal 930 157 50Normaal 1140 163 40 297

Table 3-3 downgrading of roses

3.4. Timing data

To make a proper simulation, the timing of certain actions need to be measured. Some actions are measured separately for each bunch station because there could be some difference caused by wear or settings.

The actions which are measured are:

- the amount of roses rejected after a fork change and creating a bunch - the time to grab a bunch in a bunch station and put it on a belt

- the time in between putting the last bunch on the belt and the transfer of bunches to the v-belt - the tact time of the sealers

Amount of roses rejected after a fork change and creating a bunch

On a random day after production, an experiment is done with all the bunch stations. The settings are adjusted in a way that all the roses are sent to one bunch station. 50 roses are attached to the sorting machine and a video of the particular bunch station is made. From the video analysis the following accepting and rejecting sequences are determined. The amount of roses accepted or rejected is shown chronological from the top down in Table 3-4. The sequence for accepting one entire bunch is shown and repeats for each new bunch.

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14 Bunch stations 2, 4, 8, 10 Bunch stations 1, 3, 7, 13, 14 Bunch stations 5, 6, 11, 12 Bunch station 9

Accepted Rejected Accepted Rejected Accepted Rejected Accepted Rejected

3 3 3 3 2 8 9 11 3 3 3 3 2 9 10 12 4 4 4 4 6 9 10 12

Table 3-4 amount of roses accepted/rejected sequence

Bunch station 2 and 4 are modified and speeded up, thereby the amount of roses rejected is significantly less compared to the other bunch stations. The other bunch stations should all act the same, but that is not the case. The differences shown in Table 3-4 are probably caused by wear. This is a direct opportunity to improve the throughput of the machine.

The average time between each fork is extracted from the roses datasheet and appears to be 0.33 seconds. The time to change a fork or create a bunch is defined by the amount of roses rejected multiplied by 0.33.

Time to grab a bunch in a bunch station and put in on a belt

This action is split up into three parts. The first part consist out of opening the door, and the mechanical arm grabbing the bunch and locate it above the belt. During this part there cannot be a fork change. The second part consists out of dropping the bunch on the belt and the third part consist out of returning the mechanical arm and closing the door. During the second and third part, fork changes can occur until the bunch station is full.

Station 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Part 1 5.04 3.81 5.70 3.89 4.58 5.20 4.00 4.33 4.58 4.74 4.76 4.47 5.00 5.21

Part 2 6.32 4.90 6.98 4.81 5.72 6.60 5.50 5.12 5.80 6.02 5.90 5.71 6.54 6.58

Part 3 4.54 3.06 5.66 5.03 5.12 4.72 4.40 3.76 5.78 5.62 5.68 2.84 4.92 6.41

Table 3-5 timing of grabbing a bunch and put it on a belt in seconds

The result is shown in Table 3-5. It can be seen that there are differences between the bunch stations. These differences seem very small but go up to more than two seconds. In two seconds 6 roses pass the bunch station.

Time in between putting the last bunch on the belt and the transfer of bunches to the v-belt

This time is measured for each belt, but there was barely any difference between the belts. Belt 1 up to 7 are short belts and the action takes 9.3 seconds. Belts 8 up to 14 are long, so the time will also be longer. However on belt 8 and 10 the double amount of bunches is collected so the time will be shorter. For belts 8 and 10 this action takes 9.3 seconds and for belts 9, 11, 12, 13 and 14 this takes 29 seconds.

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Priority rules belts to v-belt

A video of the transfer of bunches from the belts to the v-belt has been made. Priority rules has been distracted from the video and are listed below:

1. When no belt is transferring bunches to the v-belt and one of the belts is full, it can start transferring bunches to the v-belt

2. When a belt (belt A) is transferring bunches to the v-belt and another belt (belt B), further away from the sealer, is full and waiting until it can transfer bunches to the v-belt, it starts transferring bunches as soon as the amount of bunches is equal to the amount of empty locations on the v-belt between belt A and belt B. In this way there will be no empty places on the v-belt

3. When a belt (belt B) is transferring bunches to the v-belt, or bunches originating from belt B are still on the v-belt and another belt (Belt A), closer to the sealer is full and waiting until it can transfer bunches to the v-belt, it starts transferring bunches as soon as the last bunch of belt B passed belt A.

4. When a belt (Belt A) is transferring bunches to the v-belt and multiple other belts are full and waiting until they can transfer bunches to the v-belt. The first belt in row, from belt A to the right, has priority to the other belts waiting. Depending on the situation rule two or three occurs.

5. When a belt (Belt B) is transferring bunches to the v-belt and another belt (Belt A), closer to the sealer is full and waiting until it can transfer bunches to the v-belt, it is possible that another belt also becomes full. When this belt is previously in row from belt A to the right, rule four still occurs.

Tact time of the sealers

The tact time for both of the sealers are equal and 5.81 seconds. This means that every 5.81 seconds one bunch could be packed. And each 5.81 second a new bunch could be transferred to the v-belt.

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4. Simulation model

The simulation of the rose sorting and packing machine is made with Matlab & Simulink (“Mathworks products,”),(Gray, 2007). Matlab is a programming language and Simulink is a block diagram environment which is in this case used for simulation. In particular SimEvents and Stateflow are used within Simulink, which are both event based modelling products. Simevents is a discrete-event simulation engine and makes it possible to work with entities, which travel through queues, servers, switches, gates etc. Decisions about the routing and timing of the products have to be made. A part of these decision logic is done by standard blocks such as logical operators (AND Ports, OR ports, compare to constant etc.). Another part of the decision logic is done by Stateflow, which makes it easier to make more extensive decision schemes.

4.1. Situation to be modelled

The situation which is modelled and validated with reality is the sorting machine with the first fourteen bunch stations, belts, buffer belts, two v-belts and two sealers.

4.2. Simulation model construction

The overview of the block diagram is shown in Figure 4-1 .Most of the blocks visible in this figure are subsystems and consist out of many other blocks. The overview as shown in Figure 4-1 will be discussed in this section, each individual subsystems will be discussed into more detail in Appendix A.

 Create roses: In this subsystem entities which the name rose are generated and the properties, which are called attributes in Simulink are set.

 Scanner: The scanner assigns one or more values to the attribute “bunchstation” for each rose. The value is based on the attributes.

 Pick bunch station: when one of the values of the rose in the attribute “bunchstation” is 1. The block “Pick bunch station 1” will try to send the rose to bunch station 1. If the bunch station is not available at that moment the rose will be sent trough to “Pick bunch station 2”.

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17 The amount of offered and rejected roses for the accessory bunch station is stored in this block.

 Not sorted: If the Rose is not accepted by any bunch station it is sent to the subsystem “Not sorted”. In this subsystem the entity is deleted and the time when it is deleted is stored.  Error: In reality there occur some errors sometimes at the bunch stations. In this downtime

no roses can be accepted. Because the first goal is to match reality also these errors has to be simulated.

 Bunch station: In the subsystem “Bunch station” the arrival time of the roses is stored and the entities are collected until there are enough roses to form a bunch. When that occurs the rose entities are deleted and a new entity which is called “bunch” is created. When a certain amount of bunches is reached, one bunch is sent to the next subsystem.

 Buffer belt: in the subsystem buffer belt acts as a buffer for the belt. Normally when the belt is being emptied on the v-belt, no new bunches can be dropped on the belt. Due to this buffer belt one or two bunches can be dropped when the belt is being emptied

 Belt: In the subsystem the amount of bunches which go in a bucket are collected. When the right amount of bunches is reached, no new bunches can be sent to the belt. When the belt is full, with decision logic it is determined if the belt may sent the bunches to the v-belt.  V-belt: the v-belt sends the bunches with the speed of 1 bunch per 5.5 s to the Sealer.  Sealer: In the sealer time is simulated to seal the bunches and the bunches are deleted. The

arrival time of the bunches is stored.

4.3. Result 1, amount of offered accepted and rejected roses

There are two important outputs of the simulation the first one is the amount of roses offered, accepted and rejected per bunch station. This is shown in Table 4-1 and Figure 4-2. This result is only important to be compared to the reality. This is done in the next chapter.

Bunch station 1 2 3 4 5 6 7 8 9 10 11 12 13 14

offered 545 2950 474 3936 1584 664 851 6783 69 3006 697 2211 1514 1484

accepted ₅₁₀ ₂₅₅₆ ₄₅₀ ₃₂₇₉ ₁₃₄₇ ₅₆₅ ₇₈₂ ₄₄₃₄ ₆₈ ₂₃₀₉ ₅₁₈ ₁₇₄₁ ₁₂₆₇ ₁₂₇₀ rejected 35 394 24 657 237 99 69 2349 1 697 179 470 247 214

Table 4-1 Amount of roses offered, accepted and rejected in the simulation

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4.4. Result 2, rejected roses per bunch station per reason of rejection

The most interesting result is the amount of roses which are rejected at each bunch station for what reason. The first step is to identify the different causes for rejecting a rose at a bunch station. Five rejecting causes are identified and listed below:

1. Fork changed: While a full fork is being changed no roses can be accepted at the bunch station.

2. Bunch created: While a bunch is created no roses can be accepted. After each third fork change a bunch is created.

3. Bunch handled: When a bunch is grabbed by the mechanical arm to put it on the conveyer belt, the forks cannot be changed. So during this process only three roses can be accepted before the fork has to be changed.

4. Bunch waiting: when the mechanical arm is in the right position to drop the bunch on the belt, the forks can be changed again. It is possible that there is no space to drop the bunch on the buffer belt. In this case the bunch is waiting. Roses can be accepted until the bunch station is full.

5. Error: when the bunch station is in an error state, no roses can be accepted.

The amount of roses per cause and per bunch station is counted in the simulation. The result is shown in Figure 4-2, Figure 4-3, Table 4-1 and Table 4-2. In Figure 4-2 the amount of roses accepted and rejected is shown and in Figure 4-3 the amount of roses rejected per reason is shown. It is notable that bunch stations which are not used that intensively nearly only rejects roses because the fork has to be changed. The bunch stations which are speeded up also rejects roses when a bunch is created. This is because the time to create a bunch is much higher than the time to change the fork. At the normal bunch station this is not the case. Another thing to notice is the amount of roses rejected when a bunch is handled or waiting. This only seems to occur at the more intensively used bunch station, two, four, five, eight, ten, twelve, thirteen and fourteen. The part bunch waiting at station eight is extremely high compared to the other stations. The amount of roses rejected caused by errors in the bunch stations also seems dependent on the amount of roses offered to a station. However this amount is relatively small compared to the other causes.

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19

Table 4-2 amount of roses rejected per cause per bunch station

1 2 3 4 5 6 7 8 9 10 11 12 13 14 % Fork changed 35 150 12 268 211 53 56 594 1 246 143 415 226 190 49,4 Bunch created 0 115 0 211 0 0 3 437 0 154 0 2 0 0 17,5 Bunch handled 0 18 0 36 2 0 0 374 0 104 4 14 4 0 10,6 Bunch waiting 0 17 0 28 0 0 0 820 0 62 0 73 12 0 19,2 error 0 0 2 24 14 1 0 82 0 31 2 7 8 0 3,3

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5. Model validations

Multiple methods to verify the model are used. The first method is to compare the output of the simulation with the data displayed in Table 3-2 and see if the same amount of roses which are offered, accepted and rejected per bunch station in the simulation comply with the reality. The other method is to simulate individual parts of the system for a short time and verify if the exact same thing happens as in reality.

5.1. Verification with available data

In the simulation, the roses of the roses datasheet from May 11 are used as input, and the bunch station settings of May 11 are used (Table 3-1). If the simulation leads to the same amount of roses offered, accepted and rejected per bunch station, this part of the verification is considered to be approved. However slight differences could occur due to errors at the sealer which are not logged and therefore can’t be simulated.

Bunch station 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Real offered 546 2950 474 3936 1585 615 857 6783 74 2988 673 2188 1576 1492 Real accepted 511 2596 443 3283 1357 532 783 4448 72 2315 517 1656 1303 1297 Real rejected 35 354 31 653 228 83 74 2335 2 673 156 532 273 195 Simulation offered 545 2950 474 3936 1584 664 851 6783 69 3006 697 2211 1514 1484 Simulation accepted 510 2556 450 3279 1347 565 782 4434 68 2309 518 1741 1267 1270 Simulation rejected 35 394 24 657 237 99 69 2349 1 697 179 470 247 214 Difference offered -1 0 0 0 -1 49 -6 0 -5 18 24 23 -62 -8 Difference accepted -1 -40 7 -4 -10 33 -1 -14 -4 -6 1 85 -36 -27 Difference rejected 0 40 -7 4 9 16 -5 14 -1 24 23 -62 -26 19 Difference offered [%] -0.2 0 0 0 -0.1 8.0 -0.7 0 -6.8 0.6 3.6 1.1 -3.9 -0.5 Difference accepted [%] -0.2 -1.5 1.6 -0.1 -0.7 6.2 -0.1 -0.3 -5.6 -0.3 0.2 5.1 -2.8 -2.1 Difference rejected [%] 0 11.3 -22.6 0.6 4.0 19.3 -6.8 0.6 -50 3.6 14.7 -11.7 -9.5 9.7 Table 5-1 comparison of simulation data and reality data

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21 The result of the simulation which makes use of the datasheet of the roses from May 11 is shown in Table 5-1. It can be seen that the difference between the amount of roses accepted in reality and in simulation is very small for each bunch station. However a small deviation in a bunch station which has an overflow to another bunch station could result in a relatively very large deviation for the overflow bunch station. This can be seen clearly in bunch station 6. In Table 3-1 It is shown that Station 1, 2 and 5 have an overflow to station 6. The difference between simulation and reality are 0, 40 and 9 roses which correspond with a percentage of 0%, 1.5% and 0.7%. These small deviations add up to a bigger deviation of 8% or 49 roses, offered too much at bunch station six. This involves also a relatively bigger deviation of 6.2% or 33 roses accepted.

5.2. Verification of bunch station with video

In section 3.4 it is explained how the time to change a fork and to create a bunch is measured. 50 roses directly after each other are sent to one bunch station.

The same situation is created in the simulation. All the Roses are sent to one particular bunch station. The result for bunch station 1 is shown in Figure 5-1 .It can be seen that the accepting and rejecting sequence is the same in simulation as in reality. The other bunch stations are validated in the same way.

5.3. Validation of v-belt with video

The priority rules of transferring the bunches from the belts to the v-belt are discussed in section 3.4. These priority rules must of course also occur in the simulation model. To show that these algorithms do occur in the model, some time intervals are picked from the simulations where one or more of these rules occur.

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22 In Figure 5-2 a) the amount of bunches on the belts ready to transfer to the v-belt is shown. When the right amount of bunches is on the belt, the bunches are transported to the end of the belt. From upon that moment all the bunches are ready to be transferred to the v-belt. In Figure 5-2 a), priority rules one, two and three are shown. At first the situation of rule one occurs. Belt four is full and ready to be unloaded and immediately starts to transfer bunches to the v-belt. Afterwards, Belt 7 gets full and rule two occurs. The amount of empty locations between belt seven and belt four is two, so belt seven waits until there are only two bunches left on belt four and then its starts to transfer bunches to the v-belt. Than belt two gets full, and rule three occurs. There are still bunches on the v-belt, so belt two has to wait until the last bunch of belt seven is passed, then it starts transferring bunches to the v-belt.

In Figure 5-2 b) the arrival of bunches at the sealer is shown. It can be seen that the same time in between each bunch is present. This shows that there are no empty places on the v-belt.

In Figure 5-3, priority rules four and five are shown. At first Belt seven is full and immediately starts transferring bunches to the v-belt. Then belt five gets full and has to wait until the last bunch of belt seven has passed. During this waiting period Belt two gets full and receives priority over belt two.

Figure 5-2

a) amount of bunches waiting to be transferred to the v-belt b) arrival of bunches at the sealer

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23

Figure 5-3

a) amount of bunches waiting to be transferred to the v-belt b) arrival of bunches at the sealer

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24

6. Conclusion

Not only as result of the simulation but also during the analysis and construction of the simulation model answers to the research questions has been found. At first the sub questions will be answered to form an answer to the main research question. Besides there will be recommendations for further research on this subject.

6.1. Answers to research questions

How many roses are currently downgraded?

the exact amount of roses downgraded can be found in Table 3-3. About 8% of the roses is downgraded. This implies an opportunity to improve the system.

What are the possible causes for rejecting roses at a bunch station

During the analyses of the process these causes are identified: - Fork is being changed

- Bunch is created

- Bunch is handled by the mechanical arm - Bunch is waiting to be transferred to a belt - Error in bunch station

How many roses are rejected for each separate cause.

The exact answer can be seen in Table 4-2.

However the biggest part of rejected roses is caused by forks which are changed. The more intensively a bunch station is used, the bigger the part of roses rejected caused by bunch handling and bunches waiting becomes.

Which factors impose restrictions in throughput for the entire machine or parts of the machine?

Many factors which impose restrictions have been found: - Time to change forks

- Time to create bunch

- Time to transfer bunch from bunch station to belt - Tact time of v-belt

- Priority rules (belts to v-belt) - Sorting settings

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25

Recommendations

All the factors mentioned in the conclusion, influence the amount of roses which could be accepted at the right bunch station. Probably it is for all these factors possible to gain little or much improvement. However the costs of the possible improvements and the extra profit must be in proper balance. Hence it is recommended to think up possible improvements and use the simulation to calculate the extra profit. This extra profit could be compared to the costs for the improvement. A few possible improvements to the machine which could be further calculated are:

- Introduce one or more extra bunch station(s). - Speed up more bunch stations.

- Give the more intensively used bunch stations a higher priority at transfer from belt to v-belt. - Introduce extra quality classes.

- Make sure there is space available for more bunches on the buffer belts.

- Change settings of bunch stations to make the processes of creating a bunch faster. - Get rid of differences between bunch stations discussed in section 3.4.

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Bibliography

Cassandras, C. G., & Lafortune, S. (2010). Introduction to Discrete Event Systems (2nd ed.). Boston: Springer.

Gray, M. A. (2007). Discrete Event Simulation: A Review of SimEvents.

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Appendix A. Simulation model construction

Matlab code to import data from the roses sheet and run the simulation:

%% load rose properties

Rose_Batch = sortrows(readtable('11mei2016_2.csv'),3); Rose.Stem_Length = table2array(Rose_Batch(:,'StemBend90')); Rose.Group = table2array(Rose_Batch(:,'StationNo'));

Rose.Timestamp = (datenum(Rose_Batch{:,'TimeStamp'}, 'yyyy-mm-dd

HH:MM:SS.FFF')-datenum(Rose_Batch{1,'TimeStamp'}, 'yyyy-mm-dd HH:MM:SS.FFF'))*24*3600; Rose.Timestamp = [Rose.Timestamp; max(Rose.Timestamp)+120];

Rose.Timestep = diff(Rose.Timestamp); %Rose.Timestep = [Rose.Timestep];

starttime = datetime(datestr(Rose_Batch{1,'TimeStamp'})); load('Bunchstation1_Error.mat'); load('Bunchstation2_Error.mat'); load('Bunchstation3_Error.mat'); load('Bunchstation4_Error.mat'); load('Bunchstation5_Error.mat'); load('Bunchstation6_Error.mat'); load('Bunchstation7_Error.mat'); load('Bunchstation8_Error.mat'); load('Bunchstation9_Error.mat'); load('Bunchstation10_Error.mat'); load('Bunchstation11_Error.mat'); load('Bunchstation12_Error.mat'); load('Bunchstation13_Error.mat'); load('Bunchstation14_Error.mat'); load('Belt1_Error.mat'); load('Belt2_Error.mat'); load('Belt3_Error.mat'); load('Belt4_Error.mat'); load('Belt5_Error.mat'); load('Belt6_Error.mat'); load('Belt7_Error.mat'); load('Belt8_Error.mat'); load('Belt9_Error.mat'); load('Belt10_Error.mat'); load('Belt11_Error.mat'); load('Belt12_Error.mat'); load('Belt13_Error.mat'); load('Belt14_Error.mat'); %% set parameters

t_Stop = max(Rose.Timestamp); % [s] simulation time

t_Bunch_Belt_Transport = 5.81; % [s] time to transfer bunch on v-belt 1 position

t_Bunch_Belt_Short = 9.3; % [s] when belt is full time before transfer to v-belt

t_Bunch_Belt_Long = 29; %

n_Bunch_In_Bunchstation = 3; % [-] maximum amount of bunches in bunchstation n_1 = 5; % [-] amount of bunches to fill one bucket n_2 = 6; % n_3 = 5; % n_4 = 6; % n_5 = 5; % n_6 = 6; % n_7 = 5; % n_8 = 12; % n_9 = 5; % n_10 = 12; % n_11 = 6; % n_12 = 6; % n_13 = 6; % n_14 = 6; %

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28 Matlab function to define the bunch station a rose is sent to:

forks (maximum 5 per fork)

%% calculate switch case fork filling input if isempty(find(Rose_Fork_Sequence==1)) Port1=11; else Port1=find(Rose_Fork_Sequence==1); end if isempty(find(Rose_Fork_Sequence==2)) Port2=12; else Port2=find(Rose_Fork_Sequence==2); end if isempty(find(Rose_Fork_Sequence==3)) Port3=13; else Port3=find(Rose_Fork_Sequence==3); end if isempty(find(Rose_Fork_Sequence==4)) Port4=14; else Port4=find(Rose_Fork_Sequence==4); end if isempty(find(Rose_Fork_Sequence==5)) Port5=15; else Port5=find(Rose_Fork_Sequence==5); End %% run simulation

start_time = datetime('now','format','HH:mm:ss') tic

sim('Rose_Sorting',t_Stop) clc

toc

function [ Bosstations ] = sortrose( Stem_Length,Group ) % sortering 1 (1.01)

Stem_Length_Min_1 = 270; % [cm] minimum length of stem Stem_Length_Max_1 = 450; % [cm] maximum length of stem Group_1 = 1; % [-] group

Bosstations_Sortering_1 = [16]; % [-] toegewezen bosstations % sortering 2 (1.02)

Bosstations_Sortering_2 = [14 16]; % [-] toegewezen bosstations % sortering 3 (1.03)

Bosstations_Sortering_4 = [4 10 11 12]; % [-] toegewezen bosstations % sortering 5 (1.05)

Stem_Length_Min_5 = 630; % [cm] minimum length of stem Stem_Length_Max_5 = 730; % [cm] minimum length of stem Group_5 = 1; % [-] group

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29 % sortering 6 (1.06)

Bosstations_Sortering_6 = [1 6 ]; % [-] toegewezen bosstations % sortering 7 (1.07)

Bosstations_Sortering_9 = [3 7 9]; % [-] toegewezen bosstations % sortering 10 (4.01)

Bosstations_Sortering_15 = [8 10 11 12]; % [-] toegewezen bosstations % sortering 16 (9.03)

Bosstations_Sortering_16 = [5 6]; % [-] toegewezen bosstations

% sortering 17 (12.01&12.02)

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30 % sortering 18 (13.01&13.02)

Bosstations_Sortering_18 = [18]; % [-] toegewezen bosstations % sortering 19

% alle overigen

Bosstations_Sortering_19 = [20]; % [-] toegewezen bosstations

if Stem_Length >= Stem_Length_Min_1 && Stem_Length < Stem_Length_Max_1 &&Group==Group_1 Bosstations = [Bosstations_Sortering_1 zeros(1,4-length(Bosstations_Sortering_1))];

elseif Stem_Length >= Stem_Length_Min_2 && Stem_Length < Stem_Length_Max_2 &&Group==Group_2

Bosstations = [Bosstations_Sortering_2 zeros(1,4-length(Bosstations_Sortering_2))];

else

end end

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31 subsystems belonging to bunch station 3:

Figure 18 Create_Roses

Figure 19 Error bunch station 3 Figure 17 Pick bunch station 3

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Figure 21 Buffer belt 3 Figure 20 Bunch station 3

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Figure 24 Chart 3

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Figure 27 v-belt 1

Figure 26 Sealer 1 Figure 25 V-belt 1 error