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本科生畢業(yè)設(shè)計(jì)（論文）
翻譯資料
中文題目： 以微型機(jī)器人為基礎(chǔ)的自動化
顯微操作裝置為微系統(tǒng)裝配
英文題目： A microbot-based automated micromanipulation
station for assembly of microsystems
A microrobot-based automated micromanipulation station for
assembly of microsystems
Sergej Fatikow Mirko Benz
Abstract：
The development of new types of miniaturized and microrobots with human-like capabilities play an important role in different application tasks. One of the main problem of present-day research is, for example, to assemble a whole microsystem from different microcomponents.This paper presents an automated micromanipulation desktop station including a piezoelectrically driven microrobot placed on the highly-precise x–y stage of a light microscope, a CCD-camera as a local sensor subsystem, a laser sensor unit as a global sensor subsystem, and a Pentium PC equipped additionally with an optical grabber. The microrobot has three piezoelectrically driven legs and two autonomous manipulators as endeffectors; it can perform highly-precise manipulations （with an accuracy of up to 10 nm） and a nondestructive transport （at a speed of several mm/s） of very small objects under a microscope. To perform manipulations automatically, a control system, including a task planning level and a real-time execution level, is being developed. （C）1998 Elsevier Science B.V. All rights reserved.
Keywords： Microrobots; Microassembly; Automated desktop station; Assembly planning; Piezoactuators
1.Introduction：
There is a growing need for miniaturized and microrobots worldwide. Due to the enormous breakthroughs in conventional robotics and in the microsystem technology (MST),everyone is convinced that the development of remote-controlled or autonomous microrobots will lead to improvements in many areas. Above all, positive results are expected in medicine (microsurgery),manufacturing (microassembly, inspection and maintenance), biology (manipulation of cells) and testing/measuring technique (VLSI) . Medicine is one of the application fields which would profit by the microrobotics the most. The attention lies on artificial organs (prosthetics) , laparoscopy, implantable drug delivery systems (diagnosis and therapy systems) , telemicrosurgery, etc. The minimal-invasive surgery developed into an important field of medicine during the last years.Smaller and more flexible active endoscopes are needed in order to replace human hands, respond to outer incidents, penetrate into a body or a vessel through natural bodily orifice or a small incision by remote control, where they perform complex in-situ measurements and manipulations. In order to meet these requirements, microprocessors, several sensors and actuators, a light source and possibly an image processing unit should be integrated into an intelligent
endoscope. Biotechnology requires special microstructured active tools which are able to perform micromanipulations like the sorting or reunion of cells or the injection of a foreign body into a cell under a microscope. In the gene research and the environment technique （cells as indicators for harmful substances）, precise and gentle manipulation of single cells are also required. Industry and especially manufacturing and measuring techniques need highly sensitive testing methods in the μm-range. An important task represents, for example, the inspection of wafers, where several check points have to be contacted by a temperature or voltage probe. The same is valid for inspection robots which are used in inaccessible or dangerous terrain in order to detect leaks or flaws and make repairs （e.g., in pipelines）。The adoption of MST-related developments by the industry has already demonstrated which kind of problems occur with the mass production of microsystems. These systems usually consist of microcomponents of different materials which are produced with various microtechniques; this leads to one or several very precise assembly step （s）of the
individual components. The assembly of microsystems, i.e., the non-destructible transport, precise manipulation or exact positioning of microcomponents is becoming one of the most important applications in microrobotics.
2. Manipulation of microobjects：
The availability of highly precise assembly processes will make it easier to economically realize operable microsystems. In order to efficiently produce microsystems and components in lot sizes or by mass-production techniques, it is absolutely necessary to introduce flexible, automated, precise and fast microassembly stations. Different concepts are being followed to do micromanipulation for particular
classes of application.
Purely manual micromanipulation is the most often used method today. In medicine and biological research, it is used exclusively. Even in industry, microassembly tasks are very often carried out by specially trained technicians, who, for example, preposition assembly parts using screws and springs, then position the parts with tiny hammers and tweezers, and finally fasten them in the desired position. However, with increasing component miniaturization, the tolerances become smaller and smaller, and the capabilities of the human hand are no longer adequate.
The application of partially automatic micromanipulation systems of conventional size, which are teleoperated; thereby, the hand motions of the human operator are translated into finer 3D motions for the manipulators of the manipulation system by means of a joystick or mouse. Here, the dexterity of the human hand is supported by sophisticated techniques. However, the fundamental problem of the resolution of the fine motion and of the speed remain, since the motion of the tool is a direct imitation of that of the operator’s hand.
The use of automated multifunctional micromanipulation desktop stations’ supported by miniaturized flexible robots which employ MST-specific direct- drive principles. These robots could be mobile and are able perform manipulations in different work areas. The transport and micromanipulation units performing the assembly may be integrated onto one chip. As opposed to the aforementioned micromanipulation technique, there is no direct connection between the operator’s hands and the robot. The assembly steps may be carried out with the help of closedloop control algorithms. The human assigns all tasks to miniaturized assembly mechanisms and, by doing so, tries to compensate for his limited micromanipulation
capabilities. Many microrobots can be active at the same time in a desktop station.
The use of many flexible nanorobot systems which solve the manipulation tasks in close cooperation. Here, the robot size is comparable to that of the manipulated object. This concept could be based on the human behavior, but its realization lies in the distant future.
In general, manipulations vary from an application to another. However, approximately the same operation sequences are used in every case. They are: grip, transport, position, release, adjust, fix in place and processing steps like cutting, soldering, gluing, removal of impurities, etc. In order to be able to carry out these operations, corresponding tools are needed, such as microknives, microneedles to affix objects, microdosing jets for gluing, microlaser devices for soldering, welding or cutting, different types of microgrippers, microscrapers, adjustment tools, etc. Microgrippers play a special role, since they considerably influence the manipulation capabilities of a robot. Microgrippers can clamp, make a frictional connection or adhere to the material, depending on the physical and geometrical properties of an object. Adapting a gripper to the shape of the object to be gripped is often the best solution in the microworld, even at the cost of flexibility. This allows handling of a workpiece having a complex shape, such as a gear. Thereby, the gripper securely attaches to the contour of the part. For small, smooth parts, a suction pipette might be a practical tool. If the upper surface of a workpiece must not be touched or gripped due to technological reasons, it can be protected by a corresponding form-fit of the pipette hole. For contour clamping and frictional connections in manipulations involving fragile parts, elastic grippers made of soft plastics are preferred over metal grippers. Due to the variety of task-specific gripping tools in automated micromanipulation systems, a suitable gripper exchanger system might be necessary.
It should be mentioned that it is not always possible to adapt conventional manipulation methods to the demands of the microworld. A major problem is the effect of various forces which is completely different from the macroworld. Gravitation only plays a minor role in the microworld, but attractive forces,such as electrostatic forces or Van-der-Waals forces, are significant. Liquid surface tension can also act as an attractive force in micromanipulations if humidity is high or if a manipulator is wet. This unusual sensitivity to forces can be very irritating in a micromanipulation station. For example, it can be easier for the robot to grip and manipulate an object than to release it afterwards. On the other hand, such an adhesion force can be used to develop new gripping methods which can fundamentally differ from the familiar mechanical and pneumatic methods. In Ref. 【1】 , several interesting ideas were shown for adhesive gripping, such as electrically charging a manipulator or wetting a gripper surface by special micromachined orifices.
The performance and degree of intelligence of a micromanipulation station is low for a manual operation; it improves by going to a teleoperation and further to an automation; this is similar with conventional robots. Most micromanipulation investigations today focus on the improvement obtained by going from a purely manual to a teleoperated system【2–4】. As previously mentioned, attempts are being made to make the transmission of effects from the microworld to the operator as realistic as possible. It is important that the operator has the entire scene in his field of view and that he can see the workspace from different angles. Besides visual information, the operator should also be able to receive acoustic and force signals if possible; this may increase the accuracy of his movements and avoid destroying the microobjects. For this, force sensors are needed which are implemented into the microtools (e.g., a microgripper) . Suitable solutions are now being sought after to realize such sensors【5】.
3. Development of a flexible micromanipulation Station：
Typically, in a conventional automatic or semiautomatic assembly station, standardized mechanical parts are assembled in well-defined work positions. The robots performing the work are usually of multi-axis arm design or they are gantry systems,usually driven by DC motors. Today, it is being attempted to use these type of familiar systems for handling and assembling of miniaturized components with dimensions in the millimeter range. For example, a modular microassembly system with four degrees of freedom is currently being developed【6】.With increasing workpiece miniaturization, however,it becomes more and more difficult to use conventional manipulation robots for assembling microsystems.The manipulation accuracy is mechanically limited for conventional robots, since disturbing influences which can be neglected in the microworld, such as small fabrication defects, friction, thermal expansion or computational errors, play a large role in the microscale. Due to the mechanical drives for the actuator’s motions, these robot systems must undergo regular maintenance and are subject to mechanical wear, which makes them expensive. The assembly process in the microworld is influenced by the mass-related dynamics of the objects being handled. Different processing conditions exist for manipulating microscopically small components. The positioning accuracy and the tolerances of the micro-components lie in the nanometer range, a few orders of magnitude lower than in conventional assembly. These accuracy requirements can only be obtained with manipulators which have highly accurately drives utilizing the MST and advanced closed-loop control. Therefore, a microrobot-based flexible desktop station is of particular interest.
A new concept for an automated micromanipulation desktop station is now being investigated 【7】. The main part of the station are the piezoelectric microrobots which were presented in Refs.【8,9】.Each robot has a micromanipulating unit integrated in a mobile platform, which makes it capable of moving and manipulating. Tools can be easily exchanged. These robot properties are good preconditions for the complete sensor supported automation of manipulation processes in the microassembly station. Owing to the flexibility of the microrobot, this multifunctional desktop station can also be used for other things, such as handling biological cells or actively testing microelectronic chips with temperatureor or voltage probes. This flexibility can also be used to accommodate several robots in the station, which can cooperate and carry out manipulations. The schematic design of the micromanipulation desktop station is shown in Fig. 1.
The operations of the microassembly station may be described as follows.
The parts are first separated and placed into magazines in order to have them correctly positioned for automated assembly. This is necessary, since microcomponents are often delivered as bulk material. This step can also be automated in a powerful microassembly station, to avoid the expensive manual handling.
A microrobot removes a micromechanical component from the magazine and transfers it to a processing cell where the component can then be prepared for microassembly by other microrobots. In this step, adhesives or solder can be applied, adjustment marks taken, or other simple operations carried out.
After the part has been processed, it is gripped by a robot and brought to a microassembly cell.
If necessary, the same operations are repeated many times in order to fetch the other necessary components from a supply container and prepare them for assembly.
All components are positioned correctly, affixed to each other and adjusted. Thereafter, they are joined together by various interconnection techniques, e.g., laser spot welding, gluing, insertion, wire bonding, etc.
After assembly, a robot brings the finished component either to another work station or a microassembly cell for further processing or to an inspection cell, where all functions of the microsystem are being tested. Finally, the finished system is transported to a storage.
The entire assembly process occurs in the desktop station under an automated light-optical microscope which is equipped with a RS232-standard interface. The sphere of operation includes a highly precise positioning table with two translational degrees of freedom （x–y plane ）and a glass plate fixed on top of it. By controlling the movements of the table, each individual working cell on the glass plate can be brought under the microscope. The station has a central computer （Pentium PC） which is used for task-specific assembly planning. The necessary operational steps are defined and carried out successively. The commands of the central computer are then further processed on a lower control level, using a parallel computer system with the C167 microcontrollers. This system was reported in Ref.【10】. The central computer is coupled with the parallel computer system over serial and parallel interfaces. These commands are resolved into command sequences for all active system components （robots, microscope and positioning table） by an execution planning system, and finally performed. Thanks to the parallel computer system, the generated commands can be executed in parallel, which makes the microassembly station capable of real-time behavior. The movements of the positioning table, different microscope functions （objective changing, focusing, lighting） and every piezoactuator are controlled.
In order to automatically control the manipulation processes in the microassembly station, there must be sensor feedback. Therefore, the light-optical microscope is equipped with a CCD camera. The camera and the microscope form the local sensor system with the help of which the position of the microobjects and the robot tools must be determined. For this it supplies visual information on the robot tools and the microobjects to the central computer. The gross position of the robots on the glass plate is detected by a global sensor system which includes a laser measuring unit and another CCD camera. The visual sensor information from both the local and the global sensor systems is used by the control algorithms to generate new commands for the robots, microscope and the positioning table. Vision is supported by a frame grabber in connection with fast real-time image recognition and processing systems. The vision parameters are passed on to the parallel computer system. They are used as a set point for the control loop.
4. Planning of the microassembly：
The above description of microassembly station activities is very general and perhaps makes the assembly process sound too simple, but many problems must first be solved. After a microsystem has been designed, all tools and techniques necessary for its automated assembly should be determined, so that the microassembly station can be set up for a taskspecific operation sequence. The specified techniques and tools must take the geometry of the components of the microsystem into consideration, as well as their physical properties, such as rigidity, texture and temperature stability. Therefore, the planning phase of an automated microassembly requires a high degree of competence. Pure top-down planning in a microassembly station seems to be impossible since the selected robots and their tools determine the flexibility and the degree of automation of the station, and therefore, also determine its performance limits. One possible planning strategy is the meet-in-the-middle strategy; thereby, this intermediate interface can be on the tool level. Indeed, the main functions of assembly planning are the determination of the task-specific sequences of the elementary operations and the selection of necessary tools for carrying out the work (top-down planning) . On the other hand, the tools and the elementary operations needed for the assembly of a microsystem also require that the microrobots have specific functional properties, which may influence the robot design (bottom-up planning) .
As mentioned, for more complex assembly tasks several robots must be used together in the desktop station. Individual robots can, for example, be specialized
to take care of one or more certain assembly operations. In this case, the robots carry out their manipulation tasks in a sequence which is defined during the planning phase. For more complex operations, robots can be pooled together to do simultaneous actions with the help of several different tools (e.g., transferring or gripping of objects) . In this case, the operator’s commands are no longer transmitted one-by-one to the manipulator arms, but are applied to the entire multirobot system, e.g., by means of the ‘one-by-multiple’ method 【11】. Here, one microrobot acts as the leader of the group, it gets micromanipulation assignments from the operator and then coordinates the other microrobots to complete the task using an automatic process for communicating with the robots and then giving them the corresponding commands. If the cooperating robots are equipped with sensors, new object manipulation methods can be developed, which are based on the distributed observation of the objects. The object could be observed from two view points, for example, which would supply