In the course of 14 work stations the “technical innards” of crash-active headrests are put together.   Photo: Deprag Schulz

Crash-active headrests are a speciality of the firm Grammer AG. Recently, this component manufacturer asked the automation specialists Dreprag Schulz in Amberg to develop assembly installations for crash-active front seat headrests for use in Poland and Mexico. Headrests on car seats are today part of the passive safety system in every car. They limit forces acting suddenly on sensitive cervical vertebrae. The protection of persons in cars involved in traffic accidents continues to be one of the central priorities in car construction. Last year, there was success in reducing further the number of accident deaths. Intelligent headrests reduce the number of fatal accidents With 4500 fatalities, ten percent fewer persons died on German roads in 2009 than in the previous year. More safety in cars is one of the reasons for this welcome fall in the numbers. Intelligent headrests, which incline forwards on impact and cushion the head valuable milliseconds earlier, make their contribution to this. During strong deceleration of the vehicle during emergency braking or impact on an obstacle, it happens that, according to the physical law of momentum, the passanger’s head is initially thrown forward and then, at the moment when the vehicle comes to a standstill, thrown backwards again. Without headrests, the cervical vertebrae would be stretched backwards beyond tolerable limits. The medical consequences range from whiplash injuries via crushed nerves to cranio-cerebral injuries. Headrests are therefore compulsory for the front seats of vehicles up to 3,5 t. It is in rear collisions in particular that headrests prevent an over-stretching of the cervical vertebrae. Innovative, so-called crash-active headrests go one step further. They stop the backwards acceleration of the head at an earlier stage and thus prevent injuries to the cervical vertebrae.

Active headrests lean towards the head

Karl Meier (Kamei) is considered the inventor of the first safety headrests, presented in 1952. In the meantime there are, besides the standard headrests, also “active” models which “lean towards” the head in an accident. It is also possible to incorporate screens into headrests as part of the in-car multi-media system. The passagers in the back of the car can then watch television, surf the internet or play computer games.
Crash-active headrests of this kind are included in the product portfolio of Grammer AG in Amberg. This firm specialises in the development and production of components and systems for car interiors as well as driver and passanger sears for off-road vehicles, lorries, buses and trains. In their strongest turnover area, “automotive” products, this Bavarian manufacturer’s range includes headrests supplied to renowned car manufacturers and to vehicle system manufacturers.

Process security in assembly is the top priority

But how is a headrest actually made? As part of the passive safety system in the vehicle, care must be taken to obtain the highest precision during manufacture. Process security is the top priority: all assembly steps are monitored and documented electronically. Grammer AG recently asked automation specialists Deprag Schulz & Co., also based in Amberg, to develop new assembly installations for innovative crash-active headrests for front seats. The assembly installations are to be put into service in Grammer’s works in Poland and Mexico.

Finished headrests in 14 steps

In 14 work stages, the technical innards of the crash-active headrests are put together. These consist of three parts, known as the “ZB trigger unit”, “housing CAK” and “travelling carriage”. The starting point of the assembly line are two hand assembly stations, at which workpiece trays are fitted with a “trigger unit”, a “housing”, a “travelling carriage” and two guide springs. The worker gives the all-clear: the elements of the headrest will now be assembled, bit by bit, in the course of the journey along the assembly path.
At station 2, the assembly installation checks whether all necessary components are present and correctly positioned. Station 3 is also primarily a test station; here the “ZB trigger unit” is tested with sensors: if the relevant label is present, are the manually fitted alignment aids in order? If yes, the “trigger unit” can be mounted in the housing and snapped into place.

Man and machine work closely together

Now station 4 has been reached. With a linear transport system, two independent guide tubes are introduced into each workpiece, adjusted and positioned; two rivets are delivered by conveyor system and pressed into the “housing-CAK” and guide tubes. The journey along the assembly path to point 5, where the conveyor system presses single fixing rivets, already orientated for fitting, into the “travelling carriage” and secures them.
At station 6 the inner workings of the future headrests receive the guide springs already manually pre-inserted in the workpiece tray by the worker. They are picked up by grips, transported and placed in the “housing CAK”. Station 7 first of all checks this step, then transports separately two washers and places them with a vacuum grip on the guide tubes.
The assembly of the crash-active headrests is now far advanced. At the eighth work station, two pressure springs brought in by double grips take their place on the already fitted guide tubes. Two blank stations now follow in the assembly line; here there is room for further work modules.
Now the “carriage” is set up. The two pressure springs are positioned and put under tension, the guide tubes are orientated and the “carriage” initially placed on the workpiece tray by the operator at the beginning is fitted by machine to the “CAK housing” and clicked into position (station 11). In the event of an accident, this “carriage” moves the intelligent headrest at lightning speed towards the driver’s and passenger’s heads so that more effective protection is given than with a conventional headrest. The “carriage” mechanism is the most important function in the crash-active headrest. But is all this in working order?

Emergency operation is tested

The next step is the test for an emergency situation. At station 12 the “trigger unit” is operated, the already completely assembled CAK module springs apart, and the functioning of the finished headrest tested. The test results, including date, time and number of the worker responsible are stored by data transfer in the attached computer system and can be processed and displayed via an Excel sheet. At station 13 the finished CAK module receives a glue-on label showing the test results previously obtained at the test station.
The assembled headrest module now reachs the “end of the line”. The worker collects and packs the workpieces which the assembly system has tested and passed. Faulty parts (so-called n.i.o. parts) are separated out by the system. A corresponding fault message appears on the display in the panel for the operator, and the worker makes the necessary corrections to the parts in the repairing area.

Short cycle times result in high throughput

The assembly installations developed by Deprag Schulz for headrest production are, without the feeder equipment, 8.34 m long, 2.55 m wide and 2.40 m high. The complete machine, with all components, weighs 9500 kg. The cycle time remains below 10 s, so more than 360 headrests per hour can be manufactured in the installation.
Deprag Schulz GmbH & Co. produce screwdriving technology, assembly automation systems, compressed air motors and compressed air tools. With 600 workers, the firm has branches in more than 40 countries.

Laser measurements on linear systems: setting up for measurements. Photo: Schunk

In the assembly and testing of axis movement in machine tools and systems for positioning, measuring and handling, laser measurement recognises even the smallest movement errors. Schunk, a manufacturer of clamping and gripping technology, now also offers laser measurement as a service. Alongside high repetition accuracy, the accuracy of axis movement increasingly often plays a decisive role in modern machine tools and systems for positioning, measuring and handling. High precision components for the productronic or electronic industry, for example, can only be manufactured with µ-precision transport all the way along the axis. Laser measurement is used wherever users depend on highly precise linear motion or on high absolute precision in production or measurement processes. As as rule, it is a question here of tolerances of better than 0.005 mm over the complete path. Modern precision measurement systems – known as laser interferometry – provide the highly accurate data necessary for this. Achieving highest accuracy with precise modules and elaborate measurement technology There is a huge amount of know-how behind laser measurement technology. Bundled light is directed via beam splitters and mirrors along separate optical paths, reflected via mirrors at the end of the measured length and recombined again in the measurement device. The difference between the light beams gives rise to a specific pattern – interference bands or rings. From these, distances, angular deviations and refractive indexes can be determined. Laser interferometry is used on the one hand in research and laboratory applications, but is finding increasingly frequent use in quality control, even directly by users in their own premises. To determine positional and running accuracy, the laser interferometer is set up parallel to the axis to be tested. The optical paths are divided into a measuring beam and a reference beam. A measurement device superimposes the reflected wavefronts of the equal phase and frequency beams and converts this into a distance reading. Finally, software presents the backlash, spreading width, guideway deviation or positional deviation graphically. The basis for determining the positional accuracy is usually the commissioning criteria according to VDI/DGQ 3441 and, for straightness measurement, according to VDI/DGQ 2617. More recent guidelines are also described in DIN ISO 230-2. As high-precision measurements on linear systems often make of comparative data, an evaluation according to VDI rules is in fact more significant.

Deviations are corrected either mechanically or in the control system

In the guideway accuracy of linear systems, particular interest is directed towards angular errors, pitch and yaw angles and the resulting rotation along a guideway. The most recent laser interferometers also provide dynamic characteristic values in the form of displacement/time, speed/time and acceleration/time diagrams. These values play a particularly important role in systems for highly dynamic applications.
On the basis of the deviations, the measured systems can be corrected very exactly. This can be done either mechanically, by providing an optimum relative positioning of sub-assemblies and components, or by so-called mapping of systematic deviations such as backlash or positional deviation and compensating for them in the machine control system.

Precise measurement pays for itself

By means of laser measurement, extremely high precision can be achieved throughout the entire motion chain. Some high precision production and testing processes only become possible when this has already been applied.
There are yet other advantages in laser measurement:
The precise alignment of system components minimises wear and tear and results a longer service life for the whole system.
Laser measurement provides a basis for documentation and quality control and raises the competence of installation constructors and system integrators. It simplifies fault-finding and saves time in problems with an existing installation, e.g. after a breakdown.
For these reasons, Schunk has recently started to offer laser measurement as a service. This is of particular value to installation constructors and system integrators in ensuring and documenting the fulfilment of all specifications in the systems they supply.
On the basis of the measurements obtained, they can optimise their systems and thus raise significantly process security and service lifetime.
They obtain meaningful data regarding the accuracy of their systems and can integrate this into their documentation.
The measurements can be of assistance in dealing with customer complaints.

On-site measurement with mobile laser interferometers

With the help of mobile laser interferometers, Schunk also carry out measurements on systems on-site, where Schunk service experts determine the position, the angle of tilt and the straightness of linear systems. They also carry out dynamic measurements on installations. After measuring, Schunk evaluates the results in collaboration with the user, system integrator or the installation constructor. For Schunk, laser measurements can be made on both their own products and existing installations with components by other suppliers.
 

Solar cell production units now see in three dimensions: in the EyeScan 3D camera by EVT, laser triangulation sensor and evaluation computor are accommodated in a housing measuring only 195 mm x 90 mm x 35 mm. Photo: EVT

The new EyeScan 3D smart camera systems by EVT now open up the third dimension to users in the solar industry. A compact housing contains a pre-calibrated laser triangulation sensor and a complete evaluation computer capable of reading up to 40000 3D profiles per second. The complete evaluation software is included in the system and has drag-and-drop programming. Thanks to the large number of pre-loaded algorithms, it is easy to solve complex 3D tasks on one’s own. The standard EyeVision software, known from the EyeSpector system, has been extended by additional evaluation commands suited to applications in the solar technology industry. This means that 3D tasks can be carried out with the same ease as 2D tasks. Solar plug-in for low-cost realisation of 3D solutions in the solar field The camera system now includes an additional so-called solar plug-in. This was developed specially for the solar industry to lower the cost for realisations of 3D solutions. With the SolarEye plug-in, special tasks in the production of solar cells, solar cell strings and modules can be carried out more efficiently. The inspection system recognises material breakage in the current production run and thus raises process yield. With a series of specialised commands, the most varied application situations in the solar field can be solved in simple ways. The exact detection of microcracks and other wafer defects is important in both wafer production and solar cell manufacture in order to avoid wafer breakage and to maintain uninterrupted production. In the compact EyeScan 3D system, not only are the evaluation unit and the sensor integrated into one housing, but they are also already pre-calibrated. The pre-calibration means that the only work left to the user is the mounting of the sensor. No additional expert is needed to install or calibrate the system. The user can also replace the sensor at any time without having to recalibrate the installation himself. All that is needed is to replace the old sensor, to load the test program from the old sensor or from a safety copy onto the new sensor – and testing can continue right away.

SolarEye detects cracks and edge chipping in the wafers

The solar plug-in SolarEye recognises at an early stage frequently encountered production faults such as cracks or edge chipping in the wafers. The test system solves essential inspection tasks: it recognised corner and edge chipping, and checks dimensional accuracy as well as density and surface precision. It is also capable of determining the position on the strip and the rotational orientation of the cells for correct soldering.
The solar plug-in has been extended to include a solar module for laser scribing inspection with reading functions specially adapted for the solar industry. It is thus possible for DMC, OCR/OCV and bar-codes to be read on both silicon and solar cells.

Defective wafers are ejected from the process

Based on high-resolution cameras, faults of any kind are recognised with μ-precision. The defective wafers can then be ejected from the process, thus substantially reducing the breakage rate in production and consequently raising the direct yield. The information on solar wafer fault characteristics gathered by the evaluation software during on-going production furthermore enables continuous improvement of the production process.

Interfaces allow communication with robots

The 3D system can be connected directly to a monitor to display current production processes and measurement results. Further interfaces such as Gigabit Ethernet, RS232 or RS485 offer transfer paths for test results and image data. The comprehensive communications interfaces in the 3D system also enable both communication with robots and direct data transfer into firm software by SAP, Oracle and others. Production results are therefore accessible at any time and can be called up in real time anywhere within the firm.

Decentralised drive and positional controls are said to minimise the risks of complex installation architectures. Photo: SEW Eurodrive

The decentralised drive and positional control system Movipro-SDC by SEW Eurodrive is said to enable the construction of flexible installation architectures in production areas. The focus is on conveyor and machine applications in the automobile industry and production logistics. The advantages of decentralised control technology, we hear, are convincing: less cable, short conductor lengths and less room needed for switching cubicles. The control system offers nominal ratings between 4 and 15 kw This family of devices is distinguished, according to the maker, by a high-performance drive converter with a graded range of performance and functions. The nomimal ratings vary between 4 and 15 kW, the spectrum of motors from DRS (standard) to DRP (premium efficiency) and CMP motors, with or without sensor feedback. The parameterised converters can control both asynchronous and synchronous motors. This family of devices is said to include local I/Os and to support various retarding voltages. High level of integration leads to space saving in the switching cubicle The level of integration of functions in one compact housing leads to obvious space savings and can replace complete converter switching cubicles in the production area, the manufacture explains, at the same time simplifying integration into the installation and reducing the complexity of the installation because of the smaller number of component interfaces. Plug connections combined with exchangeable memory card and comprehensive operator software are intended to enable problem-free installation, simple commissioning and comfortable maintenance.

Communication is possible using the common bus systems

Depending on local requirements, communication can be via various bus systems: Profibus, Profinet, Devicenet, Ether-Net/IP and Modbus/TCP. The optional safety communication with Profi-Safe is said to support the latest installation concepts. With the help of the manufacturer’s parameterising and operating software, the systems can be adjusted, commissioned and maintained.

Control system is said to minimise the risks of complex installation architectures

The system reduces, we are told, costs for planning, investment and operation by standardising drive functions using parameterisable application modules. The spatial proximity of drive and electronics and the modular construction of the application is said to simplify planning and enable advance testing of individual installation modules. The risks of complex installation architectures can thus be minimised.
 

Although the tendency amongst the medical profession today is towards a preference for the manipulator, the potential uses of the robot are now generally recognised. Robots or manipulators will become increasingly important in clinical methods such as minimally invasive surgery. Photo: IPA

Assistance systems in surgery are, as a rule, robots and manipulators. While the only robots approved for use in orthopedic operating theatres have been taken off the market again, the number of elaborate manipulator systems continues to grow. There is not yet a unified definition of assistance systems in the area of diagnostics and intervention. Because of growing criticism in the press and in connection with the better-known robot systems Robodoc and Caspar in operating theatres, the term “medical robot” lost its general acceptability and was therefore simply replaced by the term assistance system. To avoid criticism from various quarters, changes of name were occasionally resorted to in the first robot developments: it was the term “medical robot” that awoke spontaneously in many people an association with medicine without a soul. Sales figures for manipulators are rising A medical robot touches the nerve in the relationship between man and machine: does help become soulless when it is provided by a robot? In the meantime, robot systems have disappeared completely from operating theatres and are only to be encountered in research laboratories. A parallel development is that, almost unnoticed by the public, sales figures for manipulators, e.g. for the da Vinci manipulator, continue to rise. Da Vinci system is controlled by joystick In the da Vinci system, the surgeon sits at a console and guides the instruments via a multi-axis joystick, with a third, mobile arm for fixing the stereo endoscope. From the medical point of view, the initial criticism of manipulators has given way in many cases to a genuine approval, even amongst the older generation of surgeons. The arguments for the use of manipulators range from easing the physical load, thanks to  a relaxed working position, to a graded, tremor-free resolution of movements. In contrast to the manipulator, the surgeon loses control, for a moment at least, of the course of the interventional measure when he uses a program-guided robot – but not the responsibility for the patient. On the other hand, the robot offers a way of carrying out measures more quickly, accurately and with systematic planning, e.g. in clearing away tumors, sewing-up blood-vessels or grinding precise implant bearings.

Potential uses for the robot are generally recognised

Although the tendency amongst the medical profession today is towards a preference for the manipulator, the potential uses of the robot have in the meantime become generally recognised. Robots or manipulators will become increasingly important in clinical methods such as minimally invasive surgery (MIC) and Natural Orifice Transluminal Endoscopic Surgery (NOTES). NOTES in particular is making new demands on the instruments available in the operating theatre, and these will not be soluble without the assistance systems of the next generation.
In a NOTES intervention, the instrument enters through a natural opening in the body, penetrating further into  the interior via an artificial opening only once inside the body. By this means, it is for example possible to carry out an appendix operation through the mouth, with the instrument being guided through a hole in the stomach wall. The motion about several axes needed in guiding such instruments is only one of many substantial arguments for the necessity of assistance systems.

Easier working is counterbalanced by elaborate preparations for the operation

Despite the numerous arguments for the use of assistance systems, there has not so far been any convincing proof of advantages in everyday clinical work resulting from use of available robots or manipulators. The simplification of work for the surgeon and better final results are counterbalanced by the greater time required for preparing the operation, the larger space required, the time taken getting accustomed to often unnatural handling and significantly higher initial investment and running costs. As far as robots are concerned, a further point is that many interventional processes today are not suitable for automation.

The problem is how to control robots within the body

The problem is how to control robots within the body. Because of the movement of tissue due to the pulse or displacement of fine, highly sensitive tissue structures within a complex anatomy, programmed or automated procedures can usually only be carried out under closed loop control. The systems Robodoc and Caspar, used for hip endoprotheses and later for knee operations, seem at first sight to be exceptions.
In both procedures, the first step is the simulation on a computer of the fitting of a thigh prothesis on the basis of spatial data from a computer tomograph (CT). Once an optimum prothesis size has been found, the path curves for the grinder are calculated and communicated to the robots in the operating theatre. Because of the very individual material parameters in human bone and the specific distribution of forces in the lower extremities, decisive information is still missing for an optimum (force-)fit for the prothesis.
These parameters cannot be obtained easily for an individual patient because one cannot simply take samples beforehand or measure precisely the distribution of forces in the body. This is only one of the reasons why, despite the seeming advantages, no better medical results have been achieved using robots.

Greater challenges are presented by interventions in soft tissue

The difficulties increase further in interventions in soft tissue, e.g. in the brain (photo 4). Because of the sensitive, microscopic structures, these regions might seem to be one of the preferred areas for using robots. Inintially, many robot systems were therefore developed for this application. Today, it is considered one of the most difficult applications and only manipulators have been used and developed.
To be able to carry out a resection automatically, an exact anatomical map would be necessary. The brain, however, cannot be tied down, and, in addition, it pulsates, so pre-operative navigational data CT or MRT is relatively inexact and cannot provide any information on the current position.

Possible use in interventions in tissue depend on measurement technology

Apart from localising information, measurement data is also necessary regarding the condition of the tissue; this is obtained by the surgeon in conventional interventions by palpation or visually. Reliable measurement of the condition and type of tissue is not yet possible, but current projects in the field of CAD (computer assisted diagnosis) lead us to expect more precise automatic tissue analysis in the foreseeable future. The successful use of robots, i.e. a substantially faster, more precise and, because of the smaller volume of resections, more conservative operation, now depends mainly on the development of new solutions in measurement technology to improve navigation (photo 5) and new, more suitable instruments.
Until the problems of navigation for robots have been solved, no serious attempts will be made to develop suitable instruments for use with robots or manipulators. Only for da Vinci for example is there, with the Endowrist, an instrument available today specially adapted for use with a manipulator (photo 6). The potential for the use of robots looks today as vast as the techonological challenges.

Operational safety is the highest priority

The technical requirements for robot systems and manipulators vary within today’s preferred application scenarios; as a rule, one resorts to industrial robots when robots are needed, but develops new systems when manipulators are used. The necessary functions and performance parameters for robot systems in the operating theatre are fundamentally similar to those for industrial applications.
In a first step, conditions such as working area, degree of freedom, working load, stiffness and precision are laid down. Differences result however from the various national regulations and safety considerations, since faulty functions can lead to catastrophic results and because robots have to work in the operating theatre without being separated off by protective barriers. Where the technical concepts became public, laws then required, for example, the fitting of redundant position measurement systems to all robots in clinical areas in order to avoid at all costs any positioning errors.
It was also stipulated that one should guarantee, at the same time, self-locking and mobility, to avoid on the one hand an uncontrolled penetration of an instrument into the body in the event of a system breakdown and, on the other hand, to enable the instrument to be removed from the patient without risk.

Complying with hygiene regulations is easy

Complying with hygiene regulations in the operating theatre, in contrast, is relatively simple with robots and manipulators today. Before the intervention starts, a protective foil is drawn over the assistance system, largely ruling out any contact between the robot and the sterile surroundings. Simple manipulator applications are mostly variants of endoscope guidance systems.
Although robots would be fundamentally suitable for this task, they are too expensive for this kind of work, too big, and require an disproportionate effort to install them at the operating table. A series of systems have been developed to work under these marginal conditions; the most widely used of these was Aesop.

The work practice in atomic power stations as a model

If the demands made on the manipulator, as in the master-slave concept in the da Vinci system, go beyond an almost static holding the instrument, it is then necessary for the manual input to be transferred with the same dynamics to the instrument. The first ideas for solving this came from working practice within atomic power stations and were often based on pulley drives.

There is great potential for optimising assistance systems

The development of assistance systems is today no longer limited by motive equipment.  There is nevertheless still great potential for optimisation, going towards more compact external dimensions while developing stronger dynamics and larger maximum loads. These specific requirements are in contrast to the small numbers actually used in operating theatres, with the result that fundamental new developments such as the DLR light construction arm for industrial applications are realised only seldom at the moment.
In a number of research projects, like the Robin system for automatic grinding of implant bearings for hearing aids (photo 7), ENT surgeons and radiologists at the University Clinic in Tübingen are currently working closely with engineers of the Fraunhofer IPA on new closed loop solutions. In this system, the resection volume is constantly remeasured and used to regulate the removal process. Theoretically, it is already possible to reduce the duration of operations with conventional systems by a substantial factor and to make decisive improvements in accuracy.

Multifunctional instruments are on the way in

Applications with MIC and NOTES in particular have led, however, to new concepts for assistance systems in the operating theatre. Instead of the large, stationary robot or manipulator systems, multifunctional instruments, hand-held and supported by manipulator systems, are appearing, enabling the automation of parts of the operation, e.g. sewing. In laboratories, concepts are being developed for such hybrid instruments, with which the advantages properties of the conventional instrument are to be combined with those of robots or manipulators. The inspiration for this comes from key technologies in microsystem technology, microelectronics and materials sciences.

Closed loop system for minimally invasive liver tumor resection

An example for an assistance system of this kind is the development of Whole’O’Hand (Holistic Glove Intervention System) by the three Fraunhofer Institutes IPA, IIS and IGD. In this system, navigation with dynamic registration, an in-line measuring techinque based on ultrasonics and an instrument exchange system supported by manipulators are linked to a closed loop system for minimally invasive liver tumor resection. In this way, resection lines are to be replanned in a pre-clinical experiment, with manipulators used for guiding the instruments with help from active constraints.
The development of assistance systems will gain momentum again in the next generation

In diagnostics, developments have gone a little farther than this already. With the Pill Cam, the patient swallows a camera in the form of a pill, with light source and transmitter, instead of an endoscopy. Images are recorded at certain intervals during the swallowing and on the way through the digestive tract and are transmitted to a receiver near the patient. This elegant progression from classical endoscopy is not always popular with doctors.  They have to evaluate carefully the hours of video material to be sure of not missing anything. First technical ideas for automatic evaluation are taken from the image processing algorithms in computer assisted diagnosis (CAD).

The pill becomes a micro-robot

In the future, the pill could be extended to become a micro-robot, with further sensors incorporated for measuring tumors, and it should be capable of at least taking up a fixed position, perhaps even of re-orientating itself. The problem in this seems at first sight to be neither the sensor nor the drive technologies, but the anchoring of objects in the body without damaging the surrounding organs.
Despite the technical challenges, the development of assistance systems has not come to an end. On the contrary, it can be observed that, with the experience of recent years and new concepts for the next generation of clinical systems, it is gaining momentum again.

Jan Stallkamp
Dr. Eng. Jan Stallkamp is Director of the Department of Production and Process Automation at the Fraunhofer Institute for Production Technology and Automation (IPA) in 70569 Stuttgart.