Innovative Means of Motion Control

Mechatronics Project Innovative Means of Motion Control

Project Report

Cheong Luk Emma Lörd Martin Wegscheider Erik Nylén Vanessa Seyda Table of content

1 Introduction...... 2 1.1 Executive Summary...... 2 1.2 Background Information...... 2 1.3 The Machine...... 2

2 Our Solution...... 3 2.1 Brainstorming & Selection of ideas...... 3 2.1.1 Methodology...... 3 2.1.2 The solution...... 3 2.2 The main physical principles...... 4 2.2.1 Electromagnetic force...... 4 2.2.2 Pressurized air...... 6 2.3 Design...... 6 2.3.1 Rail...... 6 2.3.2 Cart...... 7 2.4 Sensors & Control System...... 8 2.5 Choice of material...... 11 2.6 Cost evaluation...... 13

3 Conclusion...... 14

Appendix: Preliminary Project Report...... 15

2 1 Introduction

1.1 Executive Summary

This report details the final design to the problem presented by Tetra Pak. The task is to design a system to move mechanical parts in a linear motion. This system must enable a complete physical separation between the force producing part and the moved part. This is to be implemented in the transportation of for example cartons in Tetra Pak’s production line.

Hygiene was a predominant factor throughout the design process. The final design to the task utilizes both pneumatic and electromagnetic principles. The product is placed on a platform which is guided along a rail without physical contact. This is achieved using coupled magnets. The levitating electromagnets also function as brakes. Pressurized air from valves embedded in the rail is used to propel the platform forward. Sterilized air can be used where necessary.

1.2 Background Information

Tetra Pak was founded 1951 by Ruben Rausing and Erik Wallenberg. The company came up with a new packaging process and developed a new way to mix paper and plastic. On that way it has continued and Tetra Pak is today a world leading company in the packing industry and has offices all over the world.

Tetra Pak’s production lines involve several processes, each in series with the other. Due to the high packaging standards, each process must be performed when the product is stationary. As a result, the production line moves in an intermittent fashion. Also due to the nature of the products, hygiene must be held in high regard on the production line.

As this machine does a lot of cycles every day, wear in large scale occurs as long there is physical contact between rail and moving part. Therefore the aim should be to find a solution where there is no more direct contact between the force producing and the moving part.

1.3 The Machine

The machine this design is to be integrated on consists of a sterilized and open section. The sterilized portion is kept so by constantly blowing decontaminated air out of its

3 entrance and exit. The production line involves processes where the platform can be exposed to chemicals with corrosive properties and temperatures of up to 130°C. 2 Our Solution

2.1 Brainstorming & Selection of ideas

After reading the project description handed out by the contact at Tetra Pak, Anders Sundberg brainstorming was performed on different solutions to the problem at hand. As the project group consists of engineering students with different majors there is a very good mix of skills covering mechanical, electrical and physical knowledge. Also with a mix of German, New Zealand and Swedish students, the group has a diverse range of experience to draw from.

The method that was used for brainstorming can be described in two steps. In the first step the group simply said whatever came into our heads, some of the ideas that came up was not so feasible while others were more practical. In the second step the group was more critical regarding the ideas and used more of a spin-off brainstorming approach, where someone would come up with an idea, and then other members would add their input to it. After the brainstorming phase, several ideas were singled out and were further investigated. The biggest concern was the complete physical separation between the force producing part and the moving part. In regards to this, two principles were investigated, pneumatic and magnetic. A range of combinations of these two principles were considered as well as just utilizing one of them. Our ultimate solution consists of a combination of both. This will be described in detail further on in this report.

2.1.1 Methodology

After deciding on our solution we divided the work into different categories and allocated each member to one of them, according to their strengths. As we worked on our individual parts we met often with the group to brief everyone on the progress, and consult each other regarding problems encountered. We also had close contact with our contact person Anders Sundberg via e-mail. The work has run smoothly without any major problems and we have followed the milestones we set in the pre-project.

2.1.2 The solution The solution that we decided is a combination of pneumatic and magnetic components. The air pushes the moving part with a burst of air that will give it a large accelerating force and then we instantly start to slow it down with magnets since it is a very short distance for the part to travel. The magnets are also there to keep the moving part hovering over the rail since one of the requirements was complete physical separation.

4 2.2 The main physical principles

2.2.1 Electromagnetic force

Magnetism is a phenomenon which occurs when electrical charged objects are in motion. All materials are in some way magnetically due to movement of electrons, but the total magnetic field is negligibly small. The magnetism can be observable if the spin movement from the electrons within the material is orientated in the same direction. A material where the electrons create a combined magnetic field, without help from any external force, is called a permanent magnet (or hard magnet). In our solution there will be permanent magnets implemented in both the slider and rail.

In a soft (or electro-) magnet, the magnetism will only be there as long as some external force is making the electrons to be oriented in one direction. This is the principle of electromagnets. In our solution electromagnets will be used in the rail.

As with electric charges, two magnetic charges can either attract or repel each other depending on their orientation. This phenomenon will be utilized in our system. Mainly its repelling properties will be used to prevent the slide and rail from any physical contact.

A force of 50N must be generated to overcome gravitation force on the slide. It is difficult to calculate how large the magnetic force between the slide and the rail have to be because one must take into consideration the shape, the distance, type of permanent magnets etc to achieve some acceptable results. With the aid of a proper computer program however this can be easily done. We think that it is adequate to say that it will be not be hard to create permanent magnets and electromagnets that will repel each other with a 50N force. We based this on maglev trains (magnetic levitating trains), where this technology is used and there the load is at least a thousand times bigger.

5 Figure 1: Transrapid as an exemple for a maglev train

In our solution magnetic force will also be used as a braking system. By changing the direction of the current through the coil in the electromagnets in the rail, it is possible to change whether it will attract or repel the sledge. The figure below shows the principles of the magnetic breaking system.

Figure 2: Scetch of the magnetic breaking system.

6 2.2.2 Pressurized air

In our system, bursts of pressurized air will create the accelerating force. To create the pressured air, air will be pumped through a tube. To release the air a shut will open and high pressured air will flow out.

The accelerating force created on the slide by the air bursts are even harder to calculate than the magnetic field. The force at the opening of an air tube is

F = p*A,

Where F is the force, p is the pressure and A is the area of the opening. If this force could be perfectly used the pressure needed to accelerate a 5 kg 30 m/s², would to be

p = F/A = m*a/A = 50*30/0.005 = 300 000 Pa = 3 bar

(if the opening of the tube is 5 mm²) . In reality however there will be huge amounts of energy losses, depending on the design of the slide and the rail, and a more realistic pressure would be approximately by 10 times the evaluated pressure. Even so, 30 bar is not a problem to create in an air pump. In order to determine the real required air pressure, the system should undergo some aerodynamic tests for the specific design of the slide.

2.3 Design

2.3.1 Rail

The rail used to guide the cart is shaped like an ‘n’, with 3 holes at an angle on each side. We chose the channel shape because it saves material costs while still offering reasonable rigidity. The open bottom also makes the air pipes very accessible, allowing for easy installation and maintenance of the system.

Figure 3: The rail

7 The 6 holes, shown in Figure 3, are where pressurized air is passed through to propel the cart are angled in order to provide more force in the forward direction.

The green parts in Figure 4 indicate the electromagnets. The polarity and strength of these can be controlled individually. Used in conjunction with sensors, these electromagnets can control the levitation, velocity and stopping position of the cart very accurately. The red stripe on the sides of the rail indicates the permanent magnets used to prevent the cart from moving sideways.

Figure 4: Magnets on the rail

2.3.2 Cart

The cart has also a general ‘n’ shape as shown in figure 5. There are four circular holes on the top of the platform for additional fixtures. The inside legs are machined in such a fashion to allow for maximum thrust while creating minimum lift. The slot under the cart is dimensioned to fit around the rail with a 1mm gap on all three sides.

Figure 5: The cart

8 The legs of the cart have indents on their insides. They are shaped so that a surface is presented, normal to the thrusting jet of air. This allows for maximum force which translates to better efficiency of the system.

We chose the shape of the cart so that its motion could be easily controlled in all three dimensions. Permanent magnets orientated horizontally are placed in the bottom of the platform (see Figure 6). These are used to control movement in both vertical and forward/backward directions through interaction with the electromagnets along the top part of the rail.

Figure 6: Bottom view; permanent magnets are red

Vertically orientated permanent magnets placed on the inside of the legs of the cart (see Figure 6) which is coupled by repelling magnets located on the sides of the rail, between the indents. This is to prevent the cart from straying left and right, making contact with the rail.

The round holes on the platform are for customized mounts to accommodate for the different dimensioned cartons used in the system. When a different sized carton is to be processed, the operator would simply lift the old mount from the cart, and replace it with the new one. The distances between the holes in the lateral and forward directions are different, so that the mounts would only be able to fit in one orientation, eliminating human error.

2.4 Sensors & Control System

After deciding on the main principles, the design and the construction of these solutions for moving mechanical parts innovatively, another aspect that should be investigated is the field of automation. To be more precise: the important question is which values or variables are needed to be measured and in what way, in order to control the machine and what kind of sensors is therefore needed.

9 To fulfill the requirement of not having contact between the force producing and the moving part there is a need of controlling the distance between the moving part and the rail. Therefore the distance has to be measured. A good way to do this is by runtime measurement. More or less any kind of sound (ultrasound) or electromagnetic wave can be used here, i.e. infrared radiation or laser. If lasers are used, they will be mounted in the rail emitting light in a flashing rhythm. In the same place detectors or optical sensors are needed to detect reflected beams, like in a CD player. Furthermore the moved part needs a reflecting stripe or surface on the bottom. Should all these requirements be fulfilled, the distance between the rail and moved part can be calculated from:

d = ½ * c * t, c being the speed of light and t the measured time between emitting the laser beam and detecting it.

Figure 7: Sonar Principle

One example for a distance sensor is the product OWLG of the company WELOTEC (www.welotec.de). It fulfils all the requirements we need for this application.

10 Figure 8: Distance sensor OWLG

It is very precise, has a high resolution, a very fast reaction time and it can measure distances down to 1mm. Unfortunately, it was not possible to find out anything about the price. More about this item can be read at the following address: http://s169803863.online.de/pdf/OWLG.pdf.

Now, there is a set-distance (let’s say between 10 and 20 mm). Knowing this, the distance can be controlled in a closed loop control by calculating the difference between the set point and the measured value and designing a controller accordingly. If the distance is too big, the current in the electromagnet has to be decreased and so the repelling force is smaller. Is the distance too small, the controller has to work the other way round. The distance is controlled by adjusting the current. Furthermore, an emergency stop can be integrated, should there be any contact between the moving part and the rail. This would be detected as a 0mm gap by the sensor.

Figure 9: Principle of a closed-loop control

As said in part 2.2 it is rather hard to calculate the repelling force accurately, which makes it difficult to control, although it is very important. A solution to this is to perform several pre-tests and measure what current is needed to produce a desired repelling force for known weights. These results can be saved in a look-up table and be used for controlling the distance instead of designing a controller.

The signal that is received by the optical sensor is not only used for controlling the distance, but also for detecting where the moved part is exactly on the rail. If a signal is detected and for safety reason it can be said that the signals equals a distance smaller than 4 or 5 mm, the system can conclude that the moved part must be in this place. This is especially important for braking. In regards to the final solution, there is hardly any friction because of the levitation of the cart, it is possible that the moving part has too much speed before it reaches the next production place. In order to not stop the moving

11 part too abruptly, a braking period can be initialized a few centimeters before it, as described in part 2.2 . This has to be done in an automated way, too. Therefore a speed sensor, e.g. a tachometer, has to be used. Another idea instead of using tachometers would be using more distance sensors as mentioned above. As the sensors are placed in short intervals along the rail, the speed could be calculated from the distance between two measurements and the respective time taken for the moving part to travel this distance. If the sensor detects a speed faster than allowed at a specific point along the rail, the electromagnets have to be switched in the aforementioned way, so that a braking force is produced. In parallel, the control of the distance still has to work precisely.

Now the moved part reaches the next working position at a slower speed. There it is finally stopped with a lateral, external electromagnet, which is switched on when the position sensors in the rail have detected the moving part is in the desired position. This still fulfils the requirement of not having contact, as there only should be no contact between the force producing and the moved part. This magnet is there only for precise positioning which is another important requirement according to the project description.

Another place in the construction where control could be used is the lateral deviation. But we decided not to use a control system here, but two equally strong magnets on both sides, so that the repelling (or attracting) force has the same amount on both sides. One could say that this part is self-controlling and if there are deviations the system tries to reach the equilibrium again.

The air stream blowing from the sterilized to the non-sterilized part can remain in place as our design does not negate its effect in any way.

2.5 Choice of material

The materials which can be chosen for manufacturing the main parts of the system have to fulfill the following requirements:

 The maximum weight of the moving part is not allowed to exceed 5 kg.  The material used has to withstand certain impacts of the environment in which it is applied. That is to say that the material has to have high corrosion and chemical resistance and can be utilized in a temperature range up to 130°C.  Hygienic rules have to be considered and the material must not be toxic or reactive under a certain set of circumstances.  Both parts, the slide and the rail, should consist of non-magnetic material as electro- and permanent magnets are used for moving and breaking purposes.

As explained in the sections about the function and the design of the two different parts the rail is a hollow n-shaped profile with several bores as outlets for pressurized air. For the rail there are no such restrictions with regards to hardness or strength of the material used since there is no contact between this force producing part and the moving part. Thus, wear and damage of the rail can be excluded. The material for the rail should be

12 non-magnetic and resistant to chemical and other environmental conditions. Hence, it is possible to use austenitic stainless steel or other non-ferrous steels. These are comparably cheap and easily machined.

In regards to the material of the cart, the listed requirements and primarily the maximum weight of 5 kg are in consideration. Not only the geometry of the slide has to be considered but also the permanent magnets attached to this device have to be taken into account. Out of a wide range of possible materials which are suitable for the moving part aluminum, nylon and non-ferrous steel can be suggested. For all these materials the weight of the slide can be estimated by referring to the design presented previously. Guessing that a guide and the final product are mounted to the slide, this device should not exceed a weight of approximately 2 kg.

The volume of the cart can be mathematically determined and amounts to 1.605*10-4 m³. Knowing the density of aluminum (2700 kg/m³), nylon (1150 kg/m³) and steel (7850 kg/m³) the mass can be calculated:

4 4 mcart, Al  Al *1.605*10 m³  2700kg / m³*1.605*10 m³  0.433kg 4 4 mNylon  Nylon *1.605*10 m³  1150kg / m³*1.605*10 m³  0.185kg 4 4 mcart,Steel  Steel *1.605*10 m³  7850kg / m³*1.605*10 m³  1.2599kg

Additionally the material and consequently the weight of the magnets have to be considered. This turns out to be more difficult since information concerning this is rarely available. Nevertheless, assuming the worst case the mass of one magnet attached to the side between two air gaps is between 50 and 100 g and the weight of the magnet fixed on the inner side of the top of the slide can be estimated to have a maximum weight of 500 g. In total this would increase the weight by 1 kg. In terms of mass, all three materials are suitable. Problems occur when considering the environment of the packaging machine and impacts on the cart during service. In fact, aluminum has high corrosion resistance and is non-toxic but a problem could arise when the part gets in contact with acidic matters of food/nutrition during production. This could possibly result in the formation of soluble aluminum salts which diffuse and can be ingested later when the food is consumed. This can be avoided by coating the aluminum surface with a thin plastic layer. Nylon has the better chemical resistance as well as good thermal properties. However, a disadvantage is that the mechanical properties might change in case the plastic absorbs water. Nylon tends to absorb moisture from the surroundings so that the flexibility increases and the strength and stiffness decrease. Since the extent to which a cart made of nylon might be influenced by this is not identified and the properties and conditions on the factory floor are not known, it can not be excluded that an extremely light weight slide might be a favorable solution. In regards to the production of the slide it can be pointed out that by casting or molding the cart the magnets can be positioned in the mold so that a separate fixation is not needed. Using non-ferrous steel for manufacturing the moving part would increase the weight but at the same time decrease the production costs. Steel is comparably cheap and easily machined. The mounting of the permanent magnets has to be carried out separately. Exposing steel to a certain environment

13 necessitates possibly coating of the surface in order to achieve better resistance properties. By having highlighted the advantages and disadvantages of materials coming into question, a possibility for a choice is provided. The final decision for a material depends on the conditions on the factory floor and on the priorities of the company either to accept a slightly heavier device with lower costs or to invest more money for a light weight solution.

2.6 Cost evaluation

The cost evaluation for the purposed design is extremely difficult. Generally, one can assume that the production of the system suggested above is expensive as the main parts have to be manufactured individually. Since the solution combines existing technologies in a way which principles of already applied systems (maglev train) and principles which are not very common in industrial applications (pressurized air for acceleration) are used, it is not possible to buy the required parts off the shelf. Furthermore, the choice of material is a main factor for the cost evaluation which can not be studied in detail because the decision for this is up to the company. The costs involved in the integration of the new design into an existing packaging machine will vary depending on the current system. By only changing the transportation unit and using the already available sterilized air system to supply the air jets for accelerating the moving part the costs can be kept on a relatively low level. Compared to implementing other technologies the costs might be slightly higher but the lower costs for maintenance and repair later in service will compensate for this disadvantage. By considering all the factors, one can estimate that the costs for the system designed during this project work are reasonable and do not make the solution impossible to realize.

14 3 Conclusion

This solution to the problem consists of pneumatic and electromagnetic components. The product is placed on a platform which is guided along a rail without physical contact. The cart has permanent magnets placed on its sides and base. This is coupled with permanent magnets on the rail’s sides, and electromagnets on its surface. The result is that the platform is levitated slightly above the rail, and is prevented from lateral movement. The electromagnets, used in conjunction with sensors, also function as brakes. This braking system is chosen based on its merits of efficiency and accuracy.

On the rail, apart from the aforementioned magnets, air jets are positioned on its side. These are angled in such a way to propel the platform forward. Pneumatics was used as the driving force due to it already being available in the current system, and its cheap setup costs.

15 Appendix: Preliminary Project Report

16 Mechatronics Project Innovative Means of Motion Control

Project Report One

Cheong Luk Emma Lörd Martin Wegscheider Erik Nylén Vanessa Seyda

17 Background

The procedure of Tetra Pak’s packaging machines that is currently in use is to regularly stop and start the production line over a period of time. This means that the system is dependant on one process, so that productivity is limited by the speed of the slowest process. Therefore the production of a repetitive and closely controlled motion is needed and there is a demand for solving this problem.

Requirements & limitations

There are different needs that the solution of the problem has to fulfil. One of the most important features in this context is that it fulfils the necessary hygienic requirements. These are for example: no toxic materials, no narrow slots or other dirt catchers. Another request for the solution is that it should fit into the machine and be possible to realize with existing technology. Further on, preference would be given to the solution that is easy to use, cheap and fast.

These needs can be described in more detail. The limitations are listed below: - The length of one move is typically up to 300 mm. - The time for one move is down to 100 ms. - The parts must be stopped in predefined positions with a maximum error of 0.1 mm. - The move must accurately follow a predefined arbitrary acceleration, typically maximal 30m/s2 - The mass of the moving part is up to 5 kg. - The force producing system must when inactivated not present any dangers to man or machine. - The temperature varies between ambient and up to 80oC during the production and 130oC during machine sterilization.

By interviewing our contact person Anders Sundberg via mail we have found out some requirements. The biggest requirement is that there should be no physical contact between the force producing part and the moved part. One other very important feature should be that the part is easy to sterile since it will be moved between sterile and non sterile areas.

The project is set by Tetra Pak in corporation with the IEA department of Lunds Tekniska Högskola (LTH) and should be performed as a group work within the mechatronics class. The stakeholders of this project are the project group, which consists of five team members, Tetra Pak, with its contact person Anders Sundberg, and IEA.

18 Goal & expected result

The main goal of the project is to find a solution based on a mechatronic application to the proposed problem, within the time limit of the course in mechatronics.

Dissemination of Results

The results would be presented in detail in our final written report on the 7th of May. We will consider using CAD drawings where necessary to clarify our design. An oral presentation with visual aids will be used to summarise our solution to the project problem. We have chosen not to use a prototype since the project is of the nature that a prototype would be expensive to make and will take to much time.

Methodology

Since we are a small team of students we will work closely together and do research on existing technologies and study relevant literature. With the knowledge we gain from our research we will brainstorm until we get some different solutions that we can evaluate and improve until we find our solution. This solution will we then do calculations, drawings and analyses on to prove that this will be a good, working solution. This with our materials selection and cost calculations will be included in our final report.

Project Organisation

We are a team of five students. We have limited time due to deadlines and other courses. Our financial spending will consist of printing and photocopying relevant information and is thereby limited.

The group consists of: Emma Lörd Mechanical Engineering Team Leader Vanessa Seyda Mechanical Engineering Vice Team Leader Erik Nylen Physical Engineering Specialist Martin Wegscheider Electrical Engineering Specialist Cheong Luk Mechanical Engineering Editor

Tetra Pak contact person: Anders Sundberg

19 Schedule

Since we are a small team, we will handle almost everything with direct contact with the other team members. At this point in time we feel that it is unnecessary to set advanced gates.

Starting on the 22nd February.

Preplanning + Concepts: ½ week Development 1 week Final Development ½ week Detailed Design 1½ week Report 1 week Reserve time ½ week

Deadline 20th April

Milestones

Preliminary work Week process Important dates 7 Preplanning / Concepts First report 26 Feb Exam week 1 Development 2 Final Development 3 Detailed Design Eastern Break 4 Detailed Design / Report 5 Report /Reserve time First comp. report 20 Apr

20 Risks analysis: List of things that might jeopardise the success of this project and solution to it.  Risks - solutions

Technical risks  Computer breakdown - Backup files, remember to save often, e-mail reports to other group members  Internet breakdown - Inform other members in the group if your internet doesn’t work  Printer breakdown - Try to avoid last minute printing  Phone problems - Inform other members in the group if your phone doesn’t work

Communication risks  Misunderstanding of project. - Discuss each and everyone’s sight of view of the project so that everybody interprets the project in the same way.  Language difficulties. - Use dictionaries if necessary.  Bad group communication. - Set meetings in advance and be sure that everybody gets all the information.

Other risks  Illness - At least three students will have to attend major group meetings. If only one or two are ill the others will meet and mail assignments to the others (hopefully they are capable to work)  Other studies - inform the other members of the group if you have other studies that clash. Plan the work as long in advance as possible.  Bad time management - It is important to stick to deadlines (given by group or by others). Some reserve time is given in the schedule.