Month: December 2018

In most companies, thermal design and thermal management is still in its infancy’ says Theo Ruijl, CTO of MI-Partners and ‘Thermal effects in mechatronic systems’ trainer. Ruijl sees this fact as a huge deficiency. ‘You can’t build a precise machine if you neglect the thermal aspects.’

The largest errors in a machine are caused by vibrations and fluctuations in temperature. If you don’t have both under control, you can say goodbye to an accurate system. Unfortunately, not all designers are aware of this fact. With a leaf spring you can support a system in a statically determined manner, but many engineers are unaware of the fact that such a leaf spring is also a great thermal insulator. ‘Many developers are lacking in knowledge about thermal effects in mechatronic systems,’ says Theo Ruijl, CTO of MI-Partners and trainer of the ‘Thermal effects in mechatronic systems’ course (TEMS).

In Dutch and Belgium high tech there is a lot of knowledge about dynamics, about good design, about damping. After all, generations of mechanical engineers have grown up with the construction principles of great teachers like Rien Koster and Wim van der Hoek and the Des Duivels Picture Book. But in most companies, thermal management is still not well covered.

‘Any engineer seeking to achieve a high level of accuracy will sooner or later be confronted with thermal effects,’ says Theo Ruijl. Ruijl has been working on thermal effects in mechatronic systems for two decades. ‘Temperature variations, drift, dissipation in an actuator, energy absorption of electromagnetic waves in a lens or mirror: all of these things have an impact on the performance of a system. Of course, you can ignore them, and, for a while, things might work well. But if a competitor, who has good knowledge of thermal aspects, suddenly appears, he will overtake and leave you far behind.’

‘The technical universities produce excellent graduates and post graduates in dynamics and control technology, but they do not train students in the thermal effects in mechatronic systems,’ says Theo Ruijl, thermal effects trainer.

In the high tech industry, developers are struggling with thermal distortions and inaccuracies. ‘At ASML these challenges are currently greater than the dynamic ones,’ says Ruijl. ‘An enormous amount of light is being pumped into these machines. It is inevitable that as a result the wafer heats up and deforms. If that happens nice and evenly, then you are still able to simulate it and predict it. Unfortunately, all kinds of non-linear effects occur. Then modelling and compensation becomes very difficult,’

Thermo Fisher also highlights the subject. Ruijl: ‘Many users of electron microscopes are in the life sciences. They research biological processes that they literally freeze in order to study them properly. That means dissolving them in water and cooling the water down to the freezing point. The ice must be amorphous, not crystalline, because otherwise you can’t see anything under the microscope. You will only get that kind of structure if you cool the sample at lightning speed, at 100,000 to one million Kelvin per second. Then the frozen sample needs to be observed under the microscope. The preparation and positioning pose a huge thermal challenge. How do you keep the sample at the right temperature within high vacuum? And what effect does that have on the sensitive optical and mechatronic systems around it?’

The big loss

The fact that many companies still lack in-depth thermal knowledge is largely due to something missing in the education. ‘The technical universities produce excellent graduates and post graduates in dynamics and control technology, but they do not teach the thermal effects in mechatronic systems,’ says Ruijl firmly. He himself studied with TUE professor Piet Schellekens. ‘Since Piet Schellekens retired fifteen years ago, thermal design and metrology have been neglected. Nobody has taken these issues seriously, not even in Delft or Twente. That is a big loss. There are so many fundamental challenges in this domain. That would really require a dedicated full-time professor.’

With the arrival of Hans Vermeulen a couple of years ago, there has been a part-time professor at the Eindhoven University of Technology who has put the subject on the agenda. For his Mechatronic Systems Design group, however, advanced thermal control is one of many topics. A large part of the permanent staff of Schellekens has since left. ‘In Germany the subject is more on the map,’ says Ruijl. ‘There is a large market for machine tools in which thermal effects play a major role. German machine tool builders and knowledge institutions understand each other well on this point. They run various research projects at the Fraunhofer institutes. TEMS research programs are also running in Switzerland and Spain.’

Recycling

Despite the gap in university education, there are quite a few thermal specialists in the industry. They are all self-made people who have learned the trade in practice. For Ruijl, that process started at Philips almost twenty years ago. ‘For a long time, we have known exactly how we can model dynamics and control technology and how to integrate it into machines. In a typical design process, different specialists sit at the table so that you can develop a machine with input from all disciplines. In the old days it sometimes happened at Philips that someone at the end of such a process with a complicated finite element sum found out that thermally, it didn’t work. That is why we started to develop a competence in this field with focus on mechatronic systems.’

To calculate thermal effects, engineers reuse mathematical techniques from dynamics. This resulted in the concept of thermal mode shapes.

Right from the outset, the specialists discovered that the techniques that they have already applied in dynamics can also be used in the thermal domain. ‘In dynamics and control engineering, we use state-space models and their Eigen-frequencies and mode shapes are important quantities,’ Ruijl explains. ‘Such a model is nothing more than a set of differential equations. Thermal effects are also described with differential equations. And for mathematics it doesn’t matter whether you pass through a mechanical-dynamic or a thermal-dynamic system.’

It is not exactly the same. In the thermal domain there are no objects that behave like a mass-spring system; the temperature does not overshoot, but gradually goes back, like a first order system. Like a metal plate, if you heat it up in the middle it will cool down as soon as you remove the heat source. But it never gets colder than the environment. Temperature distribution, as a function of time, can be perfectly modelled.

Ruijl and his colleagues recycled the mathematical techniques from dynamics. ‘We still use tools from, for example, Ansys or Mathworks, to perform the calculations. The analyses of mechanical vibration shapes have since long been included in those packages. The thermal shapes are not, even though the technology is already there. When we started about twenty years ago, we asked Ansys if they could give us access to this feature. It took a long time, but now they have included a button for it. That shows that it is quite unique how we, here in the Netherlands, look at thermal effects from a mechatronic design approach. It is really different from a pure physics approach that often involves thermodynamics processes. We link thermal effects to mechatronic systems.’

Consciously incompetent

In order to get the theme fixed in the way of working of its employees, Philips developed a special training course: Thermal effects in mechatronic systems. The three-day course has since found refuge at Mechatronics Academy and is being marketed by High Tech Institute. Alongside Rob van Gils (Philips), Marco Koevoets (ASML) and Jack van der Sanden (ASML), Theo Ruijl is one of the trainers.

‘Of course, you can’t give a full training covering all topics in only three days,’ Ruijl admits. ‘The public is too broad for that; people from different technical background come to the training course. Some have never done anything with TEMS, others are already quite experienced. Some are engineers, others are control engineers.’

Dutch specialists look at thermal effects from a mechatronic design approach. That is unique in the world. For Ruijl, that started years ago with his PhD research supervised by Jan van Eijk and Piet Schellekens.

On the first day, the students receive an introduction to the physics background. ‘Heat transfer as radiation, conduction, convection,’ sums up Ruijl. ‘How do you deal with it? Many facts, tips and tricks. Then we go deeper; and we do simulations with Matlab and Simulink.’ Then the foundation has been laid. ‘The goal is for everyone to speak the same language afterwards.’

Day two deals with measurement techniques. ‘Measuring the temperature is a skill in itself,’ emphasises Ruijl. ‘In any case, there are many different sensor types. But how do you measure accurately? And where? And do I measure the temperature of the object itself or of the lamp that is shining on it? Together with Jack, I once developed a system to control the water temperature in a precise manner. With a small coil in the stream we were able to warm it up very quickly and very accurately. Then we made a nice setup for an exhibition, with beautiful Perspex tubes so that everything could be seen very clearly. Unfortunately, we didn’t manage to get the temperature stable anymore. We must have done something wrong, but what? It was so bad that the temperature fluctuated as people came along. In the end, the ceiling lighting in the hall was influencing the sensor by radiation through the transparent Perspex. You only make a mistake like that once,’ laughs Ruijl.

The students themselves will also model. Using Matlab, although this particular tool doesn’t have a special toolbox for thermal effects. ‘We also deal with a cryogenic example as a practical case,’ says Ruijl. ‘How do you measure, for example, 77 Kelvin? Which materials can you use best? Cryogenic is important for scientific experiments and builders of electron microscopes.’

What is the lesson for the TEMS students? ‘The most important thing is that they understand the language,’ Ruijl replies. ‘We also make them aware of the issues that they have to pay attention to and that they need to take into account. Consciously incompetent. That is very valuable, because manufacturers with that knowledge can catch mistakes at an early stage by looking at the project again or by getting in a specialist. Every design group should always include a thermal specialist.’

This article is written by Alexander Pil, tech editor of High-Tech Systems.

Engineers and technical professionals are used to thinking of their advisory role as related to content alone. But if they want the customer or stakeholder to take action on the advice they offer, something else is needed: acceptance from the person for whom the advice is intended. That’s where sales skills come in. Claus Neeleman trains technical experts in successful advisory sales. ‘Once you understand how the sales process works, you can advise much more effectively. Both external and internal customers. Leading to a positive effect on your company’s results.’

Consultative selling, or advisory sales, is an effective sales method and therefore receives a lot of attention. According to trainer Claus Neeleman, this attention is justified. ‘Advisory sales is the best thing for the customer, it is about finding the best solution for that customer and matching it to your own interest, namely the margin on the products or services that you sell. Advising and selling are therefore both important. The trick is to create value for the customer. That value is in good advice that yields more than what the customer pays for it. In engineering companies, engineers have an important, supporting sales role, because they know exactly what matters in terms of technical content. To sell something in the high tech environment, it is the content that sells, not the sales talk.

Claus Neeleman trains technical experts in successful advisory sales.

Neeleman has a friendly personality and an intelligent glance. He is qualified as an occupational and organisational psychologist. He has worked at an assessment agency, at a reintegration agency, and amongst other things as regional manager. ‘When you carry out an assessment, you analyse and test people, which I thought was super fun and still do. You find out how to see people’s qualities and pitfalls, with an aim to helping them improve. At the reintegration agency, that didn’t always help, because in that environment commerce plays a major role. This sometimes results in moral dilemmas. Do you help the person you have to put a lot of energy into, or the person who doesn’t cause much bother? I did this type of work mainly to help people move forward in their careers and their lives, so such choices were not what I wanted. That’s why I decided to become a trainer. Of course, I also took training courses myself and discovered that it is a fascinating field. Training is something positive. People improve after taking a training course, they like it and are enthusiastic afterwards. That gives me energy. And I find it more fun to talk and to be busy with people than to write reports at a desk.’

Lots of practice

Neeleman has been working as a trainer for some eighteen years. He focuses mainly on practical skills. ‘Many of the things that I tell you come from psychology together with insights from the field about how you can influence people and what the effects are. The content of a conversation can therefore be the same, but the strategy of transferring that content to another may differ. The best approach depends upon the situation and the people in question. I firmly believe that practice is the best way to learn how to sell, for example, in an advisory capacity. The theory behind it is not complicated at all, but to better address conversations with customers you first have to experience what it is like when you try out different behaviour.’

Teacher of the year

For several years now, Neeleman has been giving two training courses at High Tech Institute: Effective Communication Skills for engineers and Sales skills for engineers. In 2016, he was appointed trainer of the year by the High Tech Institute, with an evaluation score of 9.1 out of 10. Trainees called him impressive, inspiring and empathetic as a teacher and say that he is excellent at explaining things and tailors the course right to their needs.

In 2016, Claus became High Tech Institute’s ‘Teacher of the year’.

That is quite special, because selling is not the favourite job of technology professionals…
‘Correct. They also often think that they only give advice. But that is incorrect. What is not seen is that they use less effective strategies in conversations with the customer. The result however is noticeable: as soon as the customer puts them under pressure, they already give a discount that is not in their interest. Or they are too customer-friendly and forget to make agreements about the remuneration for their consultancy work. Or they are unclear about the costs. During an on-going contract, a sales moment belongs to every advice moment. You have to pay attention to that.

But also, in the initial phase of contact with the client, a technician must be sufficiently convincing to make the sale of a service or product succeed. How do you ensure that you come across well and generate trust? How do you give the customer the idea that you are strong enough to carry out the project? You have to create trust and adapt your communication style to the customer and what is important to him/her. Both with regard to content and personal interaction. And if you work together with an account manager you have to learn to speak one another’s language, so that you know what your colleague’s intentions are and what the other person is doing in the sales process. The sales person must of course also know when the content is important.’

That sounds pretty difficult.
‘In reality it’s not such a big deal! The theory is a tool, a model that tells you which steps to take. Analytical people, such as technicians, can handle this very well. For example, the theory is that you yourself often generate resistance from the customer. This happens, for example, if you are more concerned with your own goals than with those of the customer. Or if you put too much pressure on them. That is what we call counter-behaviour. For example, if you constantly know things better than your customer, they will start to object. And if you are too dominant in the speed at which you talk about things or try to enforce a decision, this also provokes resistance. Counter-behaviour doesn’t help you sell your solution. But if you connect with your customer and go into a constructive dialogue, you will build things. The customer then moves on with you much more smoothly. If you encounter resistance during a conversation, you can adjust it by adjusting your behaviour. For example, by leaving more of the pace during the conversation to the customer and by clearly putting his/her interests first.’

Do you yourself have to change in order to sell better?
‘That’s not necessary at all. You just remain yourself, you only choose to exhibit different behaviour in certain situations in order to be more effective in your performance. If you are aware of the way a sales process progresses and you know what works, you can determine much more effectively what effect you want to have on others. It is not about right or wrong. You can reach your goal in many ways. But if you want to bring your story on stage successfully, it will certainly help if you know how to carry out advisory sales. And you can easily do that without forcing yourself into a situation that you don’t like.

What is the secret of a successful advisory sales conversation?
‘You need two ingredients: a good sound story and acceptance by the customer. The latter refers to ensuring that the customer can accept your advice. You do this by raising questions, feelings and doubts that could prevent the customer from accepting your product or service and giving good answers. Interviewing your customer based on the signals s/he gives you is not easy for technicians, because technicians deal mainly with facts and less with emotions. But, with a little practice, they can learn how to do this.’

How does such a conversation proceed?
‘The first phase is the contact phase. Technicians often find it difficult to get through this part and prefer to go straight to the content. But the first phase is important for generating trust and for creating a good personal relationship. In this phase, you also decide what you are talking about. You show that you have thought about the customer’s problem and you indicate that you already have a few ideas. In the contact phase you also agree on your way of communicating with the customer. If you have the same communication style, that’s easy. A customer can also be very directive and want to decide quickly. As a technician you have a tendency to look at a problem from all sides, but this type of customer gets irritated by that. So, if you find that time and money are important goals for a customer, then you have to respond to that information. You will then get more space for the content later in the conversation.

In the second phase you will make an inventory, thus mapping out the customer’s needs. You have proven effective methods for that. As a result, the customer recognises the scope of his/her problem and wants to take action. You cannot achieve that by saying that they have a big problem, you do that by asking questions. This leads to a sense of urgency, the idea that something has to be done.

The third phase is the presentation of your advice, where you show your skills and influence people. In the fourth and final phase you help the customer to come to a decision by taking steps together in the decision process. This is the actual advice work.

All in all, an advisory sales conversation is more about the customer than about you. The customer is king.’

Tips from Claus

‘Be happy with critical questions or reactions, because this is the moment when you have contact about the content. When this happens don’t try to be smarter or question the question, instead, go deeper into it because there is a fear or worry hidden behind such a question. So, take a step towards the customer by using criticism as positive input. After all, the customer knows the most about the problem for which s/he needs your advice. The beauty of this is: what you learn during this training course, you can also apply in other situations inside and outside your company. Acceptance comes with every deal. It’s all about influencing.

This article is written by Mathilde van Hulzen, tech editor of High-Tech Systems.

Passive damping has been a standard tool for civil engineers and architects for quite some time. Mechanical engineers, however, designing for micron accuracy typically tried to avoid the use of damping. Now the high tech world has entered the domain of sub-nanometer precision, mechanical engineers are more and more discovering that passive damping is an effective medicine for contemporary precision ailments.

In recent years, passive damping is becoming more and more a standard tool for precision engineers. It is not a coincidence that the five-day training course Design Principles for Precision Engineering devotes a whole day to this subject. Due to the increasing importance of passive damping for systems with subnanometer position requirements, High Tech Institute-partner Mechatronics Academy, has developed a special training course in this topic. Top experts Hans Vermeulen and Kees Verbaan teach this new course Passive damping for high tech systems.

Hans Vermeulen first came into contact with passive damping at Philips CFT in the late nineties. Since mid-2000, he works at ASML, where this technology has meanwhile been implemented in various sub-systems to achieve sub-nanometer level precision. He is also a part-time professor at the TU Eindhoven for one day a week. Unhindered by the daily hectics in Veldhoven, Vermeulen is able to focus, among others, on passive damping. The fact that his lectures in this field started several years ago shows that passive damping is very much in the spotlight.

Hans Vermeulen informs that ASML is increasingly using passive damping to achieve sub-nanometer precision.

Colleague-trainer Kees Verbaan received his doctorate in robust mass dampers for motion stages in 2015. He works for the NTS Group, a first-tier supplier for high tech machine design. In his role as system architect, Verbaan sees passive damping technology as becoming well established in many high-end companies.

System architect Kees Verbaan who obtained his doctorate in robust mass dampers, now sees his professional field become well established.

In the world of gross dimensions (centimetres instead of nanometres), passive damping is encountered everywhere. Put your finger on a vibrating tuning fork or nail a large rug to the wall and you readily apply passive dampinging. The automobile industry frequently applies it to car doors. A layer of anti-banging film renders a good sound experience. When you close the door, you don’t hear the sheet metal annoyingly resonate: the damping layer provides the gentle sound that we associate with quality. The energy doesn’t stay in the material as a continuous vibration, but is transferred into heat via a layer of bitumen on the inside of the door. A rather extreme example of a passive damping design is to be found in Taipei 101, the tallest building in the eponymous Taiwanese capital. Because earthquakes and typhoons appear quite frequently, the 101-storey building is equipped with a tuned mass damper, a huge spherical mass of more than eight hundred tons that hangs at the top of the building on four ropes and is provided with large viscous dampers. In the event of vibrations caused by earthquakes or severe storms, the sphere moves out of phase, absorbing a large part of the building’s kinetic energy.’Similar techniques are also now entering  high tech,’ Hans Vermeulen says. ‘In recent years, damping layers – so-called constrained layers – have been applied in high-precision stages and tuned mass dampers are being used to suppress disturbing vibrations at specific frequencies to increase the accuracy of the entire system.’

In high tech mechanical engineering, the application passive damping has been avoided and worked around for a long time. This is mainly due to the fact that designers were able to reach their goals (and often still can) with the traditional approach of using relatively stiff structures in metal or ceramics and metal springs to get predictable behaviour.

Plastics, rubber and composites

Although the use of plastics, rubber material and composites can significantly reduce unwanted vibrations, the application has never been that popular, because the hysteretic behaviour of these materials potentially makes precision systems unpredictable. Another reason is that, for a long time, analytical tools such as finite element analysis and the necessary computers didn’t have sufficient computing power to calculate the complex behaviour necessary to properly predict the influence of passive damping in structures made from exotic materials. In recent years, however, things have changed.

It may be a truism, but it’s still very true: in the world of high tech systems, the demands for precision are constantly increasing. Semiconductor manufacturers want lithographic machines that are able to make patterns in a reliable way at sub-nanometer level precision. Biotechnologists need microscopes that allow for imaging DNA structures at atomic level and medical professionals jump rely on  diagnostic equipment with, if possible, molecular resolution. In all sectors, demands are rising, in such a way that mechanical designers and architects can no longer rely on their standard toolset.

It appears that passive damping can make a very significant contribution here. The approach has proven effectiveness, also in the high tech equipment. ‘The nice thing about damping is that a whole new box of tricks is being used,’ Verbaan says. ‘Precision engineers really benefit from a few additional pieces on their chessboard. I like that, because in a manufacturer’s traditional toolkit, there were only three full drawers. Now it turns out that there are three more and they are full of new types of tools that he didn’t use before.’ He underlines that damping is an extension of the solution space, not a replacement. ‘If you don’t master traditional design, the additions will not bring you much.’

‘When requirement were less demanding, designers were used to the  predictable solution space consisting of masses and springs,’ Vermeulen says. ‘In traditional design you have to deal with linear relationships, such as relationships between force and position or stress and strain. To limit the negative effect of amplifications at resonance, designers make sure that the natural frequencies in the system are sufficiently high enough. That translates into light and rigid designs, using low mass solutions and highly stiff materials and geometries. ‘

Monolithic leaf spring

Hooke’s law states a linear relationship between force and position or  stress and strain for linear elastic materials. This means that an elastic material  returns exactly to its original position, which is nice, because as long as you know the forces that act on the system, you can accurately predict the position. Take the example of a monolithic leaf spring, a solid block of metal that has been processed with holes and slots into a mechanism based on masses and springs. Such a structure exhibits reproducible linear behaviour, free from hysteresis. From control perspective,  however, this approach might create a problems in case higher precision is required.

Typical construction with integraed tuned mass damping. Photo: Janssen Precision Engineering.

Example of a monolithic leaf spring. A solid block of metal is processed with holes and slots into a mechanism based on masses and spring. Such a structure exhibits reproducible linear behaviour but has the disadvantage that it ‘sounds like a clock.’

In this type of design, the control system suffer from long lasting vibrations. Resonances might be excited by forces within the system itself, such as imposed motion profiles, but also due to external influences, for example floor vibrations or air displacement. Without damping, these vibrations remain in the system for a long time. The vibration cannot get rid of the vibrational energy.

Mechanical engineers tend to say: ‘it sounds like a clock,’ and in this case this is not a positive observation. High frequency resonances are generally difficult to get rid of via active control. That is why system designers always try to make sure that these types of resonances are outside the area of interest. This means that the first natural frequency is typically designed roughly five times above the bandwidth. Hence, the control system is not affected in the lower frequency range. Vibrations caused by disturbances do occur, but the effect is not limiting performance.

If the demands for accuracy increase, however, designers using the traditional approach will be forced to achieve higher natural frequencies within the design. ‘The demands are increasing,’ says program manager Adrian Rankers of Mechatronics Academy. ‘That will come to an end, because it is not manufacturable anymore.’

Aversion

The traditional approach was sufficient for high tech system designers for many years. But in their search for increasing precision, all high-end system suppliers are now looking at the possibilities of implementing passive damping. Vermeulen: ‘I dare to say that it is becoming standard in the high tech systems industry. Not everyone is familiar with it, but it is expanding.’ Verbaan: ‘The big players such as ASML, Philips, TNO and ThermoFisher have the time to develop their knowledge and conduct research.’

Vermeulen: `Damping means that you deviate from the linear elastic behaviour of materials as  defined by Hooke’s law. This is because the material converts part of the energy into heat. If you plot force against  elongation in a graph, the dissipation is expressed in the hysteresis loop. The surface of this loop is proportional to the dissipated energy: the damping that you can provide to the structure.’In addition, stiffness and damping properties of rubber are temperature- and frequency-dependent (for specialists: linear viscoelastic models can be used for rubbers). As a result, these types of damping materials have been avoided for a long time: a system can have different states under the same load conditions. Vermeulen: ‘That means uncertainty in position.’  Precision engineers have an aversion to this. ‘With damping you deviate from the linear relationship. You pass through a hysteresis loop when the force increases and decreases again, and you don’t know exactly how since not all the forces that affect the system are exactly known. Often there are disturbances from the outside and then you can end up in a position that was not predicted beforehand. We have actually sought to avoid that uncertainty for a long time. As a result, everyone in the high tech systemssector has avoided damping and has designed things traditionally using masses and springs. But at a given moment, the possibilities come to an end.’

Venom

The venom, however, is in the above mentioned hysteresis loop. It’s more complicated to predict behaviour correctly, because the system can be found in different states as mentioned. This means that operating and controlling is complex in environments where floor vibrations and small variations in air pressure or temperature cause major disruptions. A soft exhalation over a wafer stage already provides a standing wave with an amplitude of several tens of nanometers while the stages need to be controlled  at sub-nanometer level.Over the last few decades, the pursuit of the holy grail of completely predictable behaviour of guide ways has been expressed in the avoidance of friction as much as possible – also providing  energy dissipation, hence damping. ‘In many applications, Coulomb friction is not desired,’ Vermeulen says. ‘Also, rRolling elements don’t work in every situation. That is why air bearings are popular. They hardly have any friction.’IBM already used air bearings in its hard drives  in 1961. Lithographic equipment developed in the Sixties and Seventies at the Philips Physics Laboratory were equipped with virtually frictionless oil bearings, and use  air bearing technology in multiple systems these days. . Vermeulen: ‘With the classical box of tricks to design frictionless guide ways, avoiding play, and applying high-stiffness springs with limited mass, we were able to make the behaviour predictable for a long time. But for nanometer applications and beyond, this is no longer sufficient.’

Wobbly pizza disk

Until recently, the classic approach was fine for designing motion stages for wafer steppers and –scanners. By using structural metals and ceramics, such a stage can be made lightweight and stiff. The natural frequencies are high enough not to be limiting for high-bandwidth control. However, the requirement for subnanometer precision make the introduction of more rigorous steps necessary.

Verbaan, during his PhD, investigated the influence of passive damping on a positioning system for 450 millimetre wafers. Such a stage has outer dimensions of 600 mm squared. ‘At the nanometer level it is as if you have to keep a wobbly pizza disk quite with your hands,’ says Verbaan. He compared various materials, , and investigated and optimized with finite element analyses the influence of mass distributions on performance.

Such a large system is susceptible to multiple resonance frequencies. To be able to control the stage accurately, these resonances must be suppressed. ‘For one frequency it is clear how that is done, and you can also put that into a simple model. But if you have multiple resonance peaks across a broad frequency band, that is virtually impossible. Then you get a model that is too complex to handle.’

That is exactly what engineers encounter in practice. The first ‘hurdle’ that limits system performance is the first natural frequency, the frequency at which an object starts to vibrate violently when the frequency is increased.  The traditional approach is to try to increase this frequency. If the means for this are exhausted, attenuation can help to suppress the resonance amplitudes. The first eigenfrequency of a square wafer table is, for example, the torsion mode, for which two pairs of opposite corners move in phase. But at higher frequencies everything starts to rattle, due to the numerous parts and components that are attached to the table such as connectors and sensors. ’Multiple small masses that vibrate at kilohertz. They will ultimately determine the dynamic behaviour. You are not able to solve this via active filtering in the control system because there so many of them. With passive damping, however, you can solve all of that,’ says Vermeulen.

Hans Vermeulen shows how damping can reduce a resonance  peak on a graph.

Verbaan: What helps is that damping materials such as rubbers and liquids and the dampers you design with these materials, typically behave very  suitable at those high frequencies, primarily because of the frequency-dependent material properties. At low frequencies, they behave like a low-stiffness spring, and therefore give in a little bit, but at higher frequencies, they become viscous.’ Vermeulen and Verbaan’s training course makes it clear that, although you can make the field of damping extremely difficult, there are also very good rules of thumb and several very useful design principles. Verbaan: ‘Our goal is to outline the entire pallet of options and ensure that students attending the course can get to a  solution using the right approach. You can let modern computers calculate for days or even for weeks, but then you have to be a real specialist. We want to provide the course participants with various possibilities for applying damping. They are taught the backgrounds of modelling, and also the simple approach to the problem so that they can apply damping correctly. ‘

‘Potential students are people with a design principles background on the one hand,’ says Rankers. ‘They want to apply damping in practice. On the other hand, system architects will also be interested, so that they are aware of the possibilities that damping can offer.’

Kees Verbaan draws a motion training stage that needs to be kept steady  in a vertical position. All kind of forces act on such a table, varying from horizontal motors to accelerate, to vertical actuators that keep the wafer on the table at the correct height. At the first vibration mode, the opposite corners move up or down simultaneously, while the other corners move in the other direction. The result can be in the order of tens of nanometers, while the stage requires subnanometer position control.

Vermeulen and Verbaan underline that passive damping is not a ‘miracle oil’. An integral design approach is indispensable. ‘I have heard engineers  saying: leave that mistake in for now, we’ll solve it later on with controls,’ says Verbaan. He says that people sometimes come to him with systems that don’t achieve the desired performance and ask him if they can use passive damping to fix it. Verbaan: ‘Sometimes, this is dealt withtoo easily. You cannot simply forget the basicss of sound mechanical design. It all starts with light-weight and stiff design  which indisputably remains necessary, also for proper functioning of damping. The pallet of options is getting bigger, but damping is not a replacement.’In the course ‘Passive damping for high tech systems’, Verbaan and Vermeulen will explain multiple damping mechanisms in detail, such as material damping, tuned mass and robust mass damping, constrained layer damping, and Eddy current damping. Starting with damping implementations in other application areas, such as civil engineering and automotive, the focus is on design, modelling and implementation of passive damping in high-tech systems.  Stan van der Meulen, co-trainer of the course, will focus on the application of viscoelastic damping in a semiconductor wafer stage.

This article is written by René Raaijmakers, tech editor of High-Tech Systems.

Experts from TNO and trainers from T2prof are putting the finishing touches to the renewed ‘Applied optics’ training courses to commence in February in Delft and in Eindhoven. The focus shifts. There is a decrease in hard maths, giving way to demos and hands-on experiments.

The ‘Applied optics‘ course from T2prof originates from the Philips Center for Technical Training. High Tech Institute launches the course in an exclusive partnership with T2prof. The first edition dates back to 2003. Shortly before that, ASML had indicated to Philips CTT that it needed a course to give electronic engineers, mechanical engineers and chemical engineers a better understanding of the optical R&D world in which they needed to operate.

The idea behind ASML’s request was to prevent Babylonian speech confusion within research projects. If non-optical engineers were to know more about lenses, reflection, refraction, collimators, lasers and similar, they would be able to work more effectively with optical specialists within the company. This is part of a growing trend in the high tech world. Companies derive their innovative strength less and less from individuals and more and more from multidisciplinary teams. If people are able to work together more efficiently, this in turn benefits development and innovative strength.

Experts from TNO and trainers from T2prof have spent the last few months updating the training to make the content more in line with the latest technological developments. Most of the difficult maths has disappeared. This has created room for more practical matters such as optical systems, aberration correction and the interaction between light and matter. The training course runs both in Eindhoven and in Delft (TNO).

A new timetable also applies to the TNO training in Delft. In Eindhoven the course is spread over sixteen afternoon sessions for a period of eight months. In Delft that becomes eight sessions spanning both afternoon and evening, spread over sixteen weeks. The training is known to be challenging, but in recent years it has, on average, been valued by the participants at more than 8 on a scale of 10.

The ‘Applied optics’ course in Delft will be organized upon request (eight sessions spanning both afternoon and evening). Also, enrollment is open for the ‘Applied optics’ course, starting twice a year in Eindhoven (fifteen afternoons).

Historical baggage

There are normally two types of trainee, says Jean Schleipen, who has, for the past four years, been one of the three trainers in the ‘Applied Optics’ course. ‘One half readily appropriates the content and gets right down to the maths and the homework. They want to master the profession. Others need more of a global picture. Think of marketing people who find it enough to be roughly updated in all optical areas. My aim is, in addition to transferring knowledge, to fascinate and enthuse all participants for our beautiful and important field of science.’

In order to make the content stick and to place it in a broader context, Schleipen deems it essential to give students both historical baggage and deeper background information. ‘We can’t teach all the formulas and mathematical background to non-opticial engineers. But it is useful if they know where these calculations come from. If they know that Ampère, Coulomb and Faraday made discoveries in the eighteenth and nineteenth century in the field of electricity and magnetism and that afterwards a genius physicist, James Maxwell, came along, a physicist who was able to mathematically describe electromagnetic forces. And that when this physicist was juggling with his formulas, all pieces of the puzzle fell in place and a new physical constant dropped out, closely resembling the speed of light as measured at that time. He felt that there must be a connection. Maxwell’s equations still form the basis of modern optics.’

‘At the end of the nineteenth century, continues Schleipen, Hertz discovered the photoelectric effect, followed by the rise of quantum mechanics at the beginning of the twentieth century.’ ‘New insights found that particals, such as electrons, could be described as mass and as a wave. Conversely, light could behave both as a wave or a particle. Students tell me that they appreciate this kind of knowledge.’

Schleipen also wants to give background information when explaining optical-physical phenomena. ‘If you use a lens when focussing a laser beam, then the spot has a finite width. But why? You can then indicate that it is due to diffraction, and/or refraction of light. But I also want students to understand the cause of this phenomenon. That it belongs to the wave character of light. I am firmly convinced that this helps to create understanding.’

In the new training course, developed in collaboration with TNO, Schleipen has made more room for demos. His experience is that small demonstrations can be very illuminating. ‘In a simple practical demo I let students determine the distance between the tracks of a CD, DVD or Blu-ray disc. We shine a laser on a DVD, the students measure the angles of the diffracted beams, just with a tape measure. And gosh: really, to an accuracy of less than a tenth of a micrometer!’ He laughs.’’Such a test lasts ten minutes, everyone has woken up and can move onto the next module.’

Interesting natural phenomena are also discussed during the course. ‘Why do we see a rainbow, why are there sometimes two and why are the colors of these two arches inverted?’

A stable discipline

In our country, optical technology can look forward to renewed attention. For example, the top High Tech Systems & Materials sector published the Photonics National Agenda last July and in 2018 substantial subsidies for photonic chips were attributed. However, Schleipen reacts quite neutral to the question as to  whether we are dealing with a renaissance of his field. ‘We certainly play the game, but in the field of optics we are a small country, for example, when compared to Germany. Naturally we have ASML and Signify and a few dozen small and medium-sized companies that do very well in the field of photonics, but certainly not hundreds, as is the case with our Eastern neighbours.’

With this statement, Schleipen doesn’t mean to play down optics. ‘It’s primarily a very stable field because it provides a basis for an extremely wide range of subjects with many areas of application. You can find optical technology in metrology, sensors, inspection, safety, data communication, imaging, in the automotive industry and in the biomedical and life sciences.’

The new course also responds to recent developments in the field of optical phenomena and instrumentation. ‘To give an example: Imec in Leuven developed a new cmos image sensor a few years ago, which had a large range of tiny spectral filters integrated on it. These compact and potentially inexpensive hyperspectral sensors have now found their way into a whole range of new applications in healthcare.’

’In fact, the optical field is so broad that not all sub-areas can be covered in sixteen three-hour modules. ‘We could easily add four more modules, but we have to stop somewhere. We don’t deal with life sciences and biomedical technology, but the basic principles are addressed adequately. And above all: students now experience the material themselves by being able to physically turn the knobs during the weekly practical sessions. After the course, participants are sufficiently equipped, in all teams where the discussions about optics go into depth. And at home, they can explain in minute detail where the colours of a rainbow come from.’

This article is written by René Raaijmakers, tech editor of Bits&Chips.