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In Focus - Archivo Octubre 2007
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Handling in miniature –
a gripper that fits in a matchbox
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With its outer diameter of just 20 mm, the MWPG miniature-changing- parallel-gripper from SCHUNK is truly tiny. Thanks to standard interfaces, it can be combined with modules from the GEMOTEC system.
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01.10.2007 -
The tide of miniaturization has now swept into all areas of life, and is evident in our private lives, too. The computer, which just a few years ago still looked rather bulky, has mutated in no time to a smart electronic miracle that fits into your pocket. For some time now, the cell phone has been a communications all-rounder – even the electric toothbrush is evolving into an intelligent high-tech device for perfect oral hygiene! The trend of combining an increasing number of functions in the smallest possible space in virtually every area of life faces modern production and assembly with a whole new set of requirements. For assembly systems and the associated handling components must also keep pace with this miniaturization of parts. The demands facing these dwarf-sized modules are exacting: they have to be fast, highly precise and extremely flexible. Furthermore, clever technical solutions have to be found in order to outwit the physical peculiarities of the micro-environment.
The importance of microsystem technology
In Germany, microsystem technology plays a key role for growth and employment. According to figures from the German Federal Ministry for Education and Research (BMBF), 680,000 jobs are directly connected to microsystem technology – and the tendency is rising. In order for the German economy to retain and advance its leading position on the international market, developments in microsystem technology have to be rapidly implemented in products and marketed. To this end, the BMBF is making around € 260 million available between 2004 and 2009 in its framework "Microsystems" program.
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Applications in the micro-world
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Optical barcode reader
Image source: Rohwedder AG
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Micro-handling plays its most important role when miniature components have to be installed in large numbers. Rapid cycle times, high precision down to just thousandths of a millimeter and highly controlled production place extreme demands on the handling components used for this task. However, the automation specialist now has a whole range of different technologies at its disposal, from special grippers to special positioning and adjusting processes for miniature components. The areas of application are many and varied, ranging from the optical industry, where miniature lenses are fitted for sensors, through electronics to medical technology and even the watch and clock-making industry.
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The adhesion phenomenon
"Adhesion" is when materials of different kinds stick to one another. The causes of adhesion can be electrostatic attraction forces, capillary forces due to liquid bridges, intermolecular interactions (so-called van der Waals forces), or mechanical attachment. The gecko’s ability to climb up a window pane is because of adhesion. This animal sticks to the glass as a result of van der Waals forces, not – as one might think – because of suckers or adhesive fluids. In the field of micro-handling, adhesion forces are often a nuisance, because adhesion causes the components to stick to the gripper. Adhesion forces can be overcome by working in clean rooms with low humidity, using extremely smooth, hard gripping surfaces, increasing conductivity or grounding the equipment. But other measures, such as blowing off components with compressed air, wiping or gripper vibration as they are put down all help the pick & place process in microtechnology.
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Demanding requirements for components and systems
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Attachment shafts of electric toothbrushes are fitted with micro-assembly solutions.
Image source: Rohwedder AG
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In the production of ignition electrodes for Xenon headlights, gripping instruments for endoscopes or glass fibers for communications technology, a few thousandths of a millimeter make all the difference. Moreover, the micro-world is characterized by special physical conditions. The heat emitted from assembly modules causes the material of axes and grippers to expand, considerably reducing the accuracy of the systems. The low weight of the micro-components, the occurring magnetism, the static electricity and the adhesive forces that are especially high in relation to the weight of the components all make assembly more difficult and turn even the simplest pick & place operations into a challenge.
The art of the engineer is therefore tried to the utmost. Modern micro-assembly cells are fully air-conditioned. They are equipped with torsion-resistant, high-precision granite axis systems and shielded from the outside. This minimizes all disturbing influences, in order to achieve maximum precision in miniature. High-precision insertion operations boasting considerable accuracy in the mounting of components can be reproduced in a stable, semi or fully automated process.
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Other systems ensure maximum precision by actively compensating disturbing influences: the position of the gripper and the component is continuously scanned by visual sensors. Making a virtue out of necessity, researchers are working on "grippers" that make use of the components’ static charge to pick them up and put them down again following a reversal of polarity.
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Standardized interfaces
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For a long time, the decisive disadvantage of special components, which were mainly developed for individual production methods, was that they did not have uniform interfaces with the higher-level assembly system or with each other. In most cases, they had been optimized for a particular application, and could only be adapted to other assembly systems through complicated, expensive processes. In order to counter this deficiency, the DIN work committee, "Production Equipment for Microsystems", under the overall control of the Karlsruhe Research Center and SCHUNK, drew up DIN 32565.
Based on this standard, the defined interface provides the connection between the higher-level assembly system and the end effector, and ensures that the latter has a precise mechanical reference and location. Up to twelve electrical or pneumatic feed-throughs can be integrated in this interface. In addition, combining the smallest possible size with a large center opening enables the assembly location to be observed not only from the side, but through the interface as well.
On the basis of this standardized interface, individual components can now be combined as desired according to different requirements, as in a modular system.
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Micro-assembly in practice
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Gripper modules allow even the smallest of balls to be picked up.
Image source: SmarAct AG
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Standardized micro-assembly is still a young branch in automation. The first standards and consequent harmonization ensure that the doorway from individual, special production to standardization has been opened. The standard interface enables gripper tools to be changed rapidly. Take the equipment of printed circuit boards with circular, flat optical components, such as lenses and laser diodes, for example. The same assembly system is used for each individual component - vacuum grippers, in this case. Each of these grippers is equipped with an interface at the adapter end, and is temporarily stored in a rack during the assembly process. From this rack, a four-axis Scara robot can replace the gripper with the desired type in a fully automated process, with a changeover accuracy of more than 10 µm.
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MicRohCell
Image source: Rohwedder AG
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The components are also employed in micro-assembly cells, for example, which accommodate complete assembly lines in the smallest possible space. Through their standardization, desktop factories of this kind offer the maximum degree of flexibility and variability. Here, system components can be used or reused in a variety of different ways. The user benefits from high insertion accuracy, short set-up times and maximum performance reliability. The compact assembly cells achieve an accuracy of up to 2 µm. Desktop factories are employed for assembling clock and watch movements, in sensor production, the construction of micro-loudspeakers and the manufacture of electric toothbrushes.
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Innovative modules from SCHUNK
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Extremely compact: the MWS miniature changing system from SCHUNK.
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As a leading supplier in the field of automation, SCHUNK is a driving force for development in the world of micro-assembly. SCHUNK’s MWS miniature changing system, with an outer diameter of 20 or 30 mm, is an exceptionally flat, compact tool changing system for small robots. The MWS was designed for tasks in the field of microsystem technology and for handling the smallest of components, and meets the requirements of DIN 32565. It picks up both tools and handling devices, and enables not just rapid manual changing, but also the automated replacement of tools when used with the appropriate changer rack. Despite its small size, the MWS 20 has six integrated energy feed-throughs (10 in the case of the MWS 30), which can be used either as pneumatic feed-throughs or to convey electricity and signals. The large center bore makes it possible to feed through long workpieces or tools, machine workpieces using a laser or monitor the work area using an image processing system.
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MWM miniature changer rack
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The MWPG 20 miniature-changing-parallel-gripper from SCHUNK is packed with amazing details and offers a wealth of ingenious features despite its light weight of just 26 g. The gripper, with an outer diameter of a mere 20 mm consists of stainless steel, and its connecting flange has the right contour for the MWS 20 miniature changing system. This can be connected directly to the head of the MWS on the robot side, without the need for adapter plates. From this head, it is supplied with compressed air through two direct connections, with no hoses required. This system also enables it to be stored in the associated MWM change rack, which allows not only magazining, but also rapid, automated tool change.
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An application in which every micrometer counts: SCHUNK’s MWPG miniature-changing- parallel-gripper inserts lead in a propelling pencil.
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SCHUNK has developed an innovative stepless monitor to detect the position of the gripper fingers. In this system, an optical sensor (located in the changing head instead of in the gripper itself) detects the movements of the gripper jaws, thereby eliminating the need to convey the signal from the gripper to the head. In addition, the MWPG 20 features a central gripper through-bore measuring 7 mm in diameter, which can be used for feeding parts, monitoring with an image-processing system or laser machining, for example.
The MRD-S miniature rotary actuator from SCHUNK is equipped with an electrical and pneumatic rotary feed-through. The motor and the rotary feed-through are mounted on pre-loaded, precision angular contact ball bearings, which enables the module to absorb high loads in relation to its size.
The RM mini rotary modules from SCHUNK’s GEMOTEC system are among the smallest specimens in the world of their kind. The smallest size has a height of just 25.5 mm, and boasts an angle of rotation that is infinitely adjustable over the entire range, and integrated, easily interchangeable hydraulic shock absorbers. The rotary module can be inductively monitored in both end positions, and can be used in any installation position. Since they have a standardized drilling pattern, with the respective adapter plates they are compatible with many modules from the GEMOTEC system, as well as other system modules from the SCHUNK product range.
Well thought-out solutions bring enormous advantages to users
The miniature changing system from SCHUNK allows gripper and positioning components to be changed with complete flexibility during the assembly process. New flexibility in the design of micro-assembly plants contributes to a reduction in costs: thanks to standardization, assembly components are produced in greater unit numbers, and therefore more cheaply. The tools’ pneumatic and electrical connection and the important, free center opening for optical applications ensures that the concept is suitable for everyday work in the factory. And for the most demanding tasks, too.
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The MWM miniature changer rack from SCHUNK acts as a depot for various gripping and handling tools.
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In cooperation with its competent partners, SCHUNK combines expertise in gripping, positioning and optical and other sensor applications. Modularity is the decisive factor here: SCHUNK’s gripping and rotary modules, its modular assembly technology from the modular GEMOTEC system and its HSB and GAS linear axes all combine in a simple, low-cost way to achieve system solutions for automation – great and small.
Innovative driving force and partner
SCHUNK is actively involved in shaping trends and developments in micro-assembly. As one of the most innovative suppliers in automation, SCHUNK is
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a member of the "Production Equipment for Microsystems" work committee, as part of the DIN "Fine Mechanics and Optics" standards committee. |
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a founding member of the VDMA’s Microtechnology Trade Association. |
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development and sales partner to numerous businesses offering innovative solutions in the field of micro-assembly. |
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12.2007
Balance quality
Round is better
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11.2007
Patented and very impressive: the SCHUNK multi-tooth guide
Distribution of the load on many shoulders – that is the principle of multi-tooth guidance, developed and patented by SCHUNK
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10.2007
Micro-handling
Handling in miniature -
a gripper that fits in a matchbox
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09.2007
Run-out Accuracy of Toolholders
Micron’s best friend – with precision for precision
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08.2007
Service Robotics
A Sensitive Touch for Sensitive Tasks – Robots in Service Gain Independence
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07.2007
Tool Clamping
A tiny difference can have a big impact
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06.2007
Hygienic Design
High-tech creations for culinary delights
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05.2007
Reduction of set-up costs with the quick-change pallet systems
Savings potential of up to 90 percent
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04.2007
Minimum quantity lubrication - MQS
- For minimum costs and maximum protection of the environment
A possible solution in searching for the optimum lubrication system
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In Focus - 2013
In Focus - Archivo 2012
In Focus - Archivo 2011
In Focus - Archivo 2010
In Focus - Archivo 2009
In Focus - Archivo 2008
In Focus - Archivo 2007
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