In this paper a new development for microgripping will be presented. The main specific features are the on microfabrication based manufacturing, the multi gear ratio motion transmission and the one piece design of the gripper structure. The fabrication of microgripper is based on a UV- lithographic process in microstructurable, photosensitive glass. The most important feature of this new approach is the nonlinear behavior of the motion translation. Compliant mechanisms consisting of hinges with exactly calculated stiffnesses were microfabricated using the microstructuring technologies of the Microsystems. By using the integrated mechanical stop the microgripper is able to change the gearing ratio during the movement. In this way it is possible to get more gripper flexibility compared with just linear transmission (gearing). The combination of the microfabrication, backlash-free and nonlinear motion transmission make the new gripper an innovative approach for the field of microassembly. The new developed grippers were fabricated and tested successfully.
The design and the fabrication of a magnetically actuated microgripper are described. The device is designed to have an out-of-plane motion; a novel concept among the microfabricated grippers. The gripper consists of three metallic fingers, radially directed and equally spaced on a circle; each finger composed by two beams, whose motion is driven by a magnetic field. The microgripper is modeled as an elastic system of two rectilinear beams, using Euler- Bernoulli theory for small deflections. The boundary value problem is solved and the deflection of the structure is calculated as a function of the magnetic force. The microgripper is fabricated using a UV-lithography based 3D electroforming technique. Each layer of the structure is made by metal electrodeposition into a polyimide mold. Several layers are stacked by repeated deposition and the final structure is obtained by dissolving the mold. Details about the fabrication techniques are presented and discussed. Properties and problems related to the photosensitive polyimide used (such as moisture absorption, loss of adhesion, etc.) are addressed. Electroforming of nickel, copper and permalloy are performed and optimized. In particular, a nickel activating solution is applied successfully for electroforming of microstructures. A shadow mask technique for seed-layer patterning is presented and discussed. A planar electromagnetic coil is fabricated by micromolding of thick photoresist and copper electroforming into the mold. The magnetic circuit is made by electrodeposition of permalloy.
In this paper we present a new silicon microgripper for microassembly realized by photolithography and fast anisotropic silicon etching. Technological and manufacturing problems of the silicon microgripper will be described. The optimized etch process results in a high silicon etch rate of up to 6.2 micrometers /min, a good selectivity silicon/photoresist of up to 100:1, a high anisotropy, a nearly vertical etch profile, and a smooth surface topography. Excellent profile control for trench etching with a depth of about 250 micrometers and an anisotropy of better than 0.98 at a mean etch rate of 4 micrometers /min was obtained. Higher etch rates of up to 6.2 micrometers /min have been achieved resulting, however, in lower anisotropy. The developed microgripper is driven by a differential-type shape memory alloy (SMA) actuator. SMA actuators exhibit the best power- to-volume ratio of all actuators, do not release any particles, and can perform various movements like bending, elongation or twisting. Heating can easily be achieved by direct electrical current. Therefore SMA actuators are well suited for microgripper applications.
There is an increasing interest in performing assembly of microsystems (i.e. non-destructive transportation, precise manipulation, and exact positioning of microcomponents) by flexible microrobots. A microrobot-based microassembly desktop station is being developed at the University of Karlsruhe. Several prototypes of piezoelectric driven microrobots and a design of the flexible microassembly desktop station were already presented at the last years' SPIE-meetings. In this paper, some implementation results of the station's planning and control system are presented. On the planning level, a common microassembly model for a computer-aided assembly planning is suggested-which is based on geometric reasoning--and its components are discussed in detail. The feasibility criteria for the generation of feasible assembly sequences and the optimization criteria for selecting the optimal assembly plan are described. For stations employing several microrobots, a method for decomposition of an assembly plan is suggested. Since the station's microrobots are rather complicated systems, it is very hard to find a useful robot model for the control purposes. For this reason, control methods have to be used for positioning of a microrobot, which do not require an exact system model and which allow a reasonable compromise between the real-time processing and the exactness. An intelligent neural controller for positioning a microrobot has been developed.
Optical Microscopes are in use to view and image biological and industrial samples. This article describes the use of such a microscope in combination with a 3D computer vision system for micro object inspection at micron scale. Combining optics and vision algorithms can provide high resolution 3D position measurements. This paper describes new vision algorithms, their results, and several of their applications. A first part explains our principles of position measurement: First we present the interest of combining optical magnification and pattern matching, and describe in which conditions it works the best. Then we show how 2D standard pattern matching can be extended to 3D without z-scanning algorithms like autofocusing. Finally we present results showing that submicron absolute accuracy and 10 nanometers resolution can be obtained. One application is the tracking of the glass tip of a microrobot which can be used for biological single-cells manipulations. The last application is the characterization of the motion and force parameters of a Shape Memory Alloy Microgripper. In the second part we describe a passive approach to compute 3D depth information from parts in focus (passive auto focus algorithms), as well as latest developments to inspect etched micro parts being out of focus (depth computation from blurred edges). Several industrial examples like surface characterization and the measurement of holes drilled by laser will be presented and discussed. Future developments will include dynamic 3D measurements for microactuator characterization, automatic modeling and 3D visualization of dynamic behaviors like force sensing in microrobotics.
The process of micro assembly requires high precision and accuracy for the positioning of micro parts. Therefore a demand exists for very precise and accurate handling devices with a specific focus on positioning devices. This paper presents an approach using robots based on closed kinematic chains, so called parallel robots, to achieve high precision in automated micro assembly. The discussion continues on a calibration process for parallel robot structures to increase the accuracy of the robot system. However obtaining an accuracy in the range of submicrometer requires an additional sensor controlled positioning process. Hence the paper presents an approach using visual control. That approach includes the application of area based matching techniques as well as photogrammetric calibration of the camera system to increase the accuracy within the image processing.
In this paper we present a novel visual servoing framework for assembly of hybrid microelectromechanical systems (MEMS). The framework incorporates a supervisory logic-based controller that allows the use of multiple visual sensors in order to execute an assembly task. The introduction of multiple visual sensor arrays allows motion of microassembly tasks to initially be controlled `globally' and then locally using a `high precision' view. We use the technique of depth-from-focus to visually servo along the optical axis. This gives us the ability to perform full 3D micropositioning under visual control. The supervisory logic-based controller selects the relevant sensor to be used at a particular stage in the assembly process, which allows us to take full advantage of the individual sensor's attributes such as field-of-view and resolution. The combination of robust visual tracking and depth estimation within a supervisory control architecture is used to perform high-speed, automatic micro-insertions. We present results for the micro insertion task performed under this framework to demonstrate it's feasibility in assembly of MEMS.
Flexure-based compliant mechanism design enables the development of revolute joint manipulators without the backlash or Coulomb friction that impede precision position and especially force control. Additionally, due to scaling effects, the adverse consequences of Coulomb friction are exacerbated at small scales. Conventional approaches to compliant mechanism design impose several limitations, however, such as severely limited ranges of motion, poor kinematic behavior, and significant deformation under multi- axis loading. The authors have developed a new type of compliant mechanism that enables the implementation of spatially-loaded revolute joint manipulators with well- behaved kinematic characteristics and without the backlash and stick-slip behavior that would otherwise impede precision control. The primary innovation in the design is the split-tube flexure, a unique small-scale revolute joint that exhibits a considerably larger range of motion and significantly better multi-axis revolute joint characteristics than a conventional flexure. Specifically, the compliant manipulator has an approximately spherical workspace two centimeters in diameter, yet is structurally rigid along non-actuated axes. Data from the small-scale manipulator demonstrates that positioning resolution is limited by digital quantization and sensor noise, and not by more fundamental physical limitations, such as backlash or Coulomb friction.
Electromagnetic actuators play an important role in macroscopic robotic systems. In combination with motion transformers, like reducing gear units, angular gears or spindle-screw drives, electromagnetic motors in large product lines ensure the rotational or linear motion of robot driving units and grippers while electromagnets drive valves or part conveyors. In this paper micro actuators and miniaturized motion transformers are introduced which allow a similar development in microrobotics. An electromagnetic motor and a planetary gear box, both with a diameter of 1.9 mm, are already commercially available from the cooperation partner of IMM, the company Dr. Fritz Faulhaber GmbH in Schonaich, Germany. In addition, a motor with a diameter of 2.4 mm is in development. The motors successfully drive an angular gear and a belt drive. A linear stage with a motion range of 7 mm and an overall size as small as 5 X 3.5 X 24 mm3 has been realized involving the motor, a stationary spur gear with zero backlash and a spindle-screw drive. By the use of these commercially available elements complex microrobots can be built up cost-efficiently and rapidly. Furthermore, a batch process has been developed to produce the coils of micro actuator arrays using lithographic techniques with SU-8 resin. In applying these components, the modular construction of complex microrobotic systems becomes feasible.
Low speed aerodynamics and its application to microflight and microaerial vehicles is an interesting problem. Small stout wings with small areas result in low Reynolds numbers. The Re's below 103 conventional fixed wing flight is no longer possible because drag becomes the dominant force. However it is possible to induce lift using those drag forces in the same manner as some birds and insects. Flapping is a good choice for microaerial vehicles since it is a highly efficient way to produce flight and power consumption is a major concern. Both insects and birds use a complex elastodynamic system that only requires excitation at its natural frequency or some lower harmonic. The actuation device presented is based on the same flight principle of insects and small birds. It is a solid-state, resonating, elastodynamic system excited by a piezoelectric actuator. It is composed of two major components. The first component is a solid-state flexure mechanism that is used to amplify the piezoceramic output and produce the flapping motion. The second components is the piezoelectric actuator. Since piezoceramics are capacitive and possess a high energy density and efficiency they can be used to excite the device and induce a flapping motion with low power losses. This allows for long distance flights that require little energy. The complex dynamics of the device involves not only the mechanics of the actuator and flexure mechanism but the interaction of the wing and the air and the actuators driving electronics. The resulting device is an electromechanically tuned resonating microrobot actuator.
This paper describes the construction and control of a two Degree-Of-Freedom (DOF) piezoelectric actuator. This actuator is part of a 6 DOF manipulator capable of linear resolution to 2 nanometer and angular resolution to 1 arc- second. Design of this actuator differs from the existing ones in that it has a monolithic structure which enables a high bandwidth, high force realization. The actuator is controlled by the TMS320C31 Digital Signal Processor residing on a standard Pentium PC. A number of nonlinearities exist in the actuator, stemming from the geometry and materials properties. For example, coupling of the actuator elements can be modeled as a soft spring which increases scale factor at high actuation levels. In this work, a combination of feedforward (input shaping) and feedback control are applied to reduce the effects of (1) scale factor nonlinearities, (2) hysteresis, and (3) output oscillations. Application of this actuator include: optoelectronics assembly, optical fiber alignment, and semiconductor processing.
One of the critical problems in the design of autonomous insect-like mobile structures is power consumption. The independent control of several legs is energetically expensive, while the energy capacity of typical electrochemical batteries is quite small. The net result is autonomous robotic insects that have extremely limited range. The authors propose an alternative approach to this problem that enables autonomous robotic insects to exhibit extremely high movement efficiency, and thus are capable of long range missions. Specifically, the desired limb motion is obtained by designing a lightly-damped skeletal structure and exciting the skeletal structure at an appropriate resonance. The approach is called elastodynamic locomotion. Rather than altering the open-loop dynamics of the machine, as is the case with conventional-scale machine control, the control actuator serves only as an excitation source that excites the open-loop dynamics of the skeleton structure. Since the motion of the insect limbs operate at their structural resonance, the acceleration and deceleration for each motion (i.e.: stride for a walking machine) requires little power, which results in a highly efficient machine. Since the motion of the insect limbs is determined by design and not by control, the primary focus of this work is in the design of a skeletal structure that will exhibit walking motion when vibrationally excited. The paper presents some insect designs that will generate a walking motion with minimal actuation. Also analyzed are the characteristic features of the gaits produced by each design.
A new design of a linear micro vibromotor for on-substrate fine positioning of micro-scale components is presented where a micro linear slider is actuated by vibratory impacts exerted by micro cantilever impacters. These micro cantilever impacters are selectively resonated by shaking the entire substrate with a piezoelectric vibrator, requiring no need for built-in driving mechanisms such as electrostatic comb actuators as reported previously. This selective resonance of the micro cantilever impacters via an external vibration energy field provides with a very simple means of controlling forward and backward motion of the micro linear slider, facilitating assembly and disassembly of a micro component on a substrate. The double-V beam suspension design is employed in the micro cantilever impacters for larger displacement in the lateral direction while achieving higher stiffness in the transversal direction. An analytical model of the device is derived in order to obtain, through the Simulated Annealing algorithm, an optimal design which maximizes translation speed of the linear slider at desired external input frequencies. Prototypes of the externally-resonated linear micro vibromotor are fabricated using the three-layer polysilicon surface micro machining process provided by the MCNC MUMPS service.
We propose the optical multi-transmission system using pyroelectric and optical piezoelectric element as the transmitter, The Optical Energy-Information Transmission System. We apply the PLZT element to the proposed system as the pyroelectric and optical piezoelectric element. The PLZT element generates the electric charge according to the change of temperature and strength of the irradiation of ultraviolet ray. We aim at the energy supply system using the pyroelectric effect, and the information transmission system using the optical piezoelectric effect. We show the numerical model of the transmission system using the PLZT element and the simulation results of the transmitting the photo energy and information source to the electric information. Then, the experimental results explains the performance of the developed transmission system and the ability of proposed system.
In today's and tomorrow's development of new products, precise positioning and assembly of small parts is of fundamental importance. Often, such tasks require the alignment of the objects with features such as edges or surface structures. In this work, we explore force controlled pushing of microparts on a planar substrate with a micromanipulator. The pushing tool is an AFM cantilever equipped with a piezoresistive force sensor. Its coarse position, as well as the global manipulation strategy, is specified by the human operator. First, we present force measurements during typical pushing operations. Using these measurements, a sensor guided controller is implemented to maneuver the robot locally by detecting events such as hitting an obstacle or changing contact conditions. Using force/position macros, we are able to push the objects precisely to a desired location without exceeding a certain limit force. Experimental results demonstrate the ability of aligning microparts on a horizontal plane with micrometer accuracy relative to each other. For automated assembly applications there are two possibilities: the local controller presented in this paper can be integrated either in a passive global positioning system if the geometry of the problem is well defined. Conversely, a feedback system, e.g., with quantitative computer vision, can be used to cover a larger spectrum of object sizes and shapes.
It is well known that due to scale effects micro systems are frequently confronted with problems caused by surface tension induced forces, electrostatic forces, etc. because their magnitude prevails over the volumetric forces. Micro- assembly processes are especially affected by this problem since detecting and applying forces in an adequate manner is essential for an assembly operation to be a success. In order to apply the forces in a correct way we need to know what their magnitude, direction, point of application and instant at which they must be applied are. In this paper we present a technique which allows us to describe the different forces that appear in the micro-assembly domain. The role played by the different forces in an assembly operation varies quantitatively but not qualitatively as the size of the assembled parts increases or decreases. By combining dimensional analysis, similitude laws and real measurements we try to understand the behavior of the forces present in the micro-system domain. Real measurements are performed on a force detection system especially designed. The main features of this system are: simultaneous detection of forces in two directions and capability of measuring forces dynamically. Those features allow us to describe the forces that appear when inserting a pin in a hole, the forces originated by the surface tension of glue on a chip while it is approached to its final position, etc. The results obtained show that some of the forces measured are strongly influenced by parameters different from those that prevail in larger object manipulations.
It is well known that surface effect forces such as van der Waals, electrostatic, and surface tension forces dominate part interactions as part dimensions fall below approximately 100 microns. Many researchers have suggested manipulation strategies that either diminish the effect of these forces or use these forces to advantage. There is little work, however, that comprehensively analyzes, both theoretically and experimentally, the exact contributions of such phenomena as surface roughness, material properties, environmental conditions, etc. to part interactions at microscales. This paper describes our work in developing a high resolution force sensor using optical beam deflection techniques for characterizing object interactions at the microscale. The interactions among a variety of micropart shapes and materials of varying surface roughness and conductivity were analyzed under various environmental conditions. Experimental results of this analysis are presented.
There is a great demand for arrangement of micro objects smaller than 100 micrometers with high accuracy and reliability in order to construct micro devices. Since micro objects tend to adhere to other objects by electrostatic force, we can pick them up easily by contacting with a needle tip instead of grasping by tweezers. On the contrary, it is difficult to place them on a substrate. To solve this problem, we have proposed a handling method by controlling the facing area, i.e. picking up the object by contacting with the center of the tooltip plane, and placing it by contacting with the edge and also inclining the tool. However it is difficult to execute this operation by manual control, because it requires delicate control of the manipulator, not to break or flip away the object. In this study, we automate this pick-and-place operation by visual and force control. Moreover, to arrange micro objects with high accuracy and reliability, all necessary functions such as calibration, object search, and positioning are integrated, and an automatic handling system is constructed. We successfully demonstrate a completely automatic arrangement of several micro objects of 30 micrometers in diameter under SEM monitoring.
Single-crystal silicon microelectromechanical devices with thermal silicon dioxide isolation segments were fabricated with a SCREAM based process; mechanical and electrical characteristics of these devices were tested. Isolation segments (26 micrometers high, 8 micrometers long, and 2 micrometers wide) have been used to isolate 1 micrometers wide, 22 micrometers high single crystal silicon (SCS) beams. Released isolation segments and Al-Si contacts allow electronics to be embedded within SCS MEMS and bare silicon beams to be used for springs and actuators.
Excimer lasers have proven to be powerful tools for machining polymeric components used in microanalytical and microchemical separation devices. We report the use of laser machining methods to produce microfluidic channels and liquid/liquid contact membranes for a number of devices fabricated at our laboratory. Microchannels 50- to 100- micrometers -wide have been produced directly in bulk polycarbonate chips using a direct-write laser micromachining system. Wider microchannels have been produced by laser machining paths through sheets of polyimide film, then sandwiching the patterned piece between solid chips of polycarbonate stock. A comparison of direct-write and mask machining processes used to produce some of the microfluidic features is made. Examples of microanalytical devices produced using these methods are presented. Included are microdialysis units used to remove electrolytes from liquid samples and electrophoretic separation devices, both used for extremely low volume samples intended for mass spectrometric analysis. A multilayered microfluidic device designed to analyze low volume groundwater samples for hazardous metals and a fluidics motherboard are also described. Laser machining processes have also been explored for producing polymeric membranes suitable for use in liquid/liquid contactors used for removal of soluble hazardous components from waste streams. A step-and-repeat mask machining process was used to produce 0.5 X 8 cm membranes in 25- and 50-micrometers -thick polyimide. Pore diameters produced using this method were five and ten micrometers. The laser machined membranes were sputter coated with PTFE prior to use to improve fluid breakthrough characteristics.
Currently there is a strong demand for refractive optical elements made from glass in 21/2D and 3D-structures. Due to the characteristics of brittle materials like glass, only a limited number of manufacturing methods can be used to machine these materials with sub-micron resolution. Thus, current microstructures made out of glass are mainly manufactured by photolithography and etching process. Lithography techniques are only for economic purposes for a series production, but is not suitable for manufacturing prototypes or a small series. Micromachining done with Excimer Lasers in combination with high precision CNC- controlled handling systems offers flexible design possibilities for optical components. Due to the limitations of conventional machining techniques for brittle materials, a new laser machining system for material processing at a wavelength of 193 nm has been designed and built. The better absorption of 193 nm compared to 248 nm or larger wavelengths leads to damage free microstructuring of most glasses. Data generation for the volume to be ablated starts with the mathematical description of the surface shape of the optical component. The contour can be derived from a mathematical function or individual xyz-data point information from any CAD-program. A pre-processor calculates the CNC-data for laser triggering, xyz-table and the CNC- mask control. Each laser pulse leads to a material removal, defined by the illuminated surface on the workpiece as well as the energy density. Superposition or overlapping of pulses allows the creation of the desired surface. The surface roughness is determined by the wavelength as well as the chosen ablation strategy. To achieve best results, the process has to be carefully adjusted for a specific material. This technique is a sufficient method for structuring grooves in ceramics or glass as well as producing aspherical transparent optical surfaces or micro lens arrays. This paper shall describe the potential of 193 nm treatment of 3D micro surfaces with an optimized process machine and data handling system in comparison with results originating from 248 nm laser processing.
A polymer surface treatment irradiated system by XeCl excimer laser is designed, bond strengths are measured by shear test method. The bond strengths of fluorocarbon-resin with aluminous bar is improved by solutions such as water (H2O), boric acid (H3BO3), sodium hydroxide (NaOH), bluestone (CuSO4), sodium aluminate (NaAlO2) reacting with fluorocarbon-resin while XeCl excimer laser irradiating. The relationship between the adhesion force with the laser intensity and laser pulse shots are measured. The mechanism of these phenomena is discussed.
While feedback control is widespread throughout many engineering fields, there are almost no examples of surgical instruments that utilize a real-time detection and intervention strategy. This concept of closed loop feedback can be applied to the development of autonomous or semi- autonomous minimally invasive robotic surgical systems for efficient excision or modification of diseased tissue. Spatially localized regions of the tissue are first probed to distinguish pathological from healthy tissue based on differences in histochemical and morphological properties. Energy is directed to only the diseased tissue, minimizing collateral damage by leaving the adjacent healthy tissue intact. Continuous monitoring determines treatment effectiveness and, if needed, enables real-time treatment modifications to produce optimal therapeutic outcomes. The present embodiment of this general concept is a microsurgical instrument we call the Smart Scalpel, designed to treat skin angiodysplasias such as port wine stains. Other potential Smart Scalpel applications include psoriasis treatment and early skin cancer detection and intervention.