Force Sensing and Control in Micromanipulation

Ph.DDOCTOR OF PHILOSOPH

Design, characterisation and testing of SU8 polymer based electrothermal microgrippers

Microassembly systems are designed to combine micro-component parts with high accuracy. These micro-components are fabricated using different manufacturing processes in sizes of several micrometers. This technology is essential to produce miniaturised devices and equipment, especially those built from parts requiring different fabrication procedures. The most important task in microassembly systems is the manipulator, which should have the ability to handle and control micro-particles. Different techniques have been developed to carry out this task depending on the application, required accuracy, and cost. In this thesis, the most common methods are identified and briefly presented, and some advantages and disadvantages are outlined. A microgripper is the most important device utilized to handle micro-objects with high accuracy. However, it is a device that can be used only in sequential microassembly techniques. It has the potential to become the most important tool in the field of micro-robotics, research and development, and assembly of parts with custom requirements. Different actuation mechanisms are employed to design microgrippers such as electromagnetic force, electrostatic force, piezoelectric effect, and electrothermal expansions. Also, different materials are used to fabricate these microgrippers, for example metals, silicon, and polymers such as SU-8. To investigate the limitation and disadvantages of the conventional SU-8 electrothermal based microgrippers, different devices designed and fabricated at IMT, Romania, were studied. The results of these tests showed a small end-effector displacement and short cycling on/off (lifetime). In addition, the actuator part of these microgrippers was deformed after each operation, which results in reduced displacement and inconsistent openings at off state every time it was operated in a power ON/OFF cycle. One of these limitations was caused by the existence of conductors in arms of the end-effectors. These conductor designs have two disadvantages: firstly, it raises temperature in the arms and causing an expansion in the opposite direction of the desired displacement. Secondly, since the conductors pass through the hinges, they should be designed wide enough to reduce the conductor resistance as much as possible. Therefore, the wider the hinges are, the higher the in-plane stiffness and the less out of plane deflection. As a result, it increases the reaction force of the arm reducing the effect of deformation. Based on these limitations a new actuatorstructure of L-shape was proposed to reduce the effects of these drawbacks. This actuator has no conductor in the hinges or the arms of the end-effectors which reduce limitation on the hinge width. . In addition, a further development of this actuator was proposed to increase the stiffness of the actuator by doubling its thickness compared with the other parts of the griper. The results of this actuator proved the improvement in performance and reduction of the actuator deformation. This new actuator structure was used to design several different microgrippers with large displacement and suitable for a wide range of applications. Demonstrations of the capabilities of the microgrippers to be used in microassembly are presented. In addition, a novel tri-directional microactuator is proposed in this thesis. This actuator’s end-effector is capable of displacements in three different directions. This actuator was used with the other designs to develop a novel three-arm (three fingers) multidirectional microgripper. To study the microgripper displacement as a function to the heater temperature, the TCR of the conductor layer of each device was measured. Because different configurations of conductor layers were studied, a significant effect of the metal layer structure on TCR was discovered. The TCR value of gold film is reduced significantly by adding the chromium layers below and about it which were used to improve the adhesion between the gold film and the SU layers. In this thesis, a new method based on a robotic system was developed to characterise these microgrippers and to study the steady state, dynamic response, and reliability (lifetime cycling on/off). An electronic interface was developed and integrated to the robotic system to control and drive the microgrippers. This new system was necessary to carry out automated testing of the microgrippers with accurate and reliable results. Four different new groups of microgrippers were designed and studied. The first group was indirectly actuated using an L-Shaped actuator and two different actuator widths. The initial opening was 120 μm for both designs. The maximum displacement was about 140 μm for both designs. However, the actuator in the wider heater width showed more stable behavior during the cycling and the dynamic tests. The second group was based on direct actuation approach using the L-Shaped actuator. There were eight different designs based on this method with different heater conductor shape, actuator width, and arm thickness. The initial opening was 100 μm and there were different displacements for the eight designs. The study of these microgrippers proved that the actuator stiffness has a significant effect on the microgripper displacement. In addition, the shape of the heater conductor has less effect. The largest displacement achieved using this method of design was about 70 μm. The third group was designed for dual mode operation and has three different designs. The initial openings were 90 μm and 250 μm. The displacement was about 170 μm in both modes. The last microgripper design was a tri-arm design for multi-mode operation. The lifetime study of SU8 based microgrippers in this thesis was the first time such an investigation was carried out. The results of IMT designs showed that the larger is the displacement the less stable is the gripper design because of the high rection force acting on the actuators. The L-shape based microgrippers had better performance and they did not break after more than 400 cycles. In addition, the studies of static displacement and dynamic response of different designed microgripper proved that better performance of the proposed actuator can be obtained by using double thickness for the actuator as compared to the arm thickness

Measurement of Z-Directional Individual Fibre-Fibre Bond Strength and Microfibril Angle Using Microrobotics

The use of microrobotics in high throughput and precise characterization of objects at microscale has been noticeably increased during recent years. Microrobotics has provided a significant added value to multiple realms e.g. biomedical research, bio-based industry, microassembly of miniature products, etc. Recently, the use of microrobotic technology in paper industry has been also commenced for measuring properties at the single fibre level. There is a large interest in the measurement of different loading modes of individual fibre-fibre bonds in pulp and paper/board industry. Among the four different modes of loading, it would be desirable for papermaking companies and paper converting companies to obtain the Z-directional strength of pulp and paper. Indeed, the Z-directional properties affect compressive properties, and accordingly the performance of structural paperboard products. Several methods have been developed to measure the Z-directional strength at a handsheet level; however, there is not any reported device capable of the Z-directional fibre-fibre bond strength measurement at a fibre level. This thesis work presents a novel method for the experimental evaluation of the Z-directional bond strength using microrobotics and a Polyvinylidene fluoride (PVDF) film microforce sensor. Due to the special dynamics of PVDF microforce sensors, the effect of the deformation rate on the performance of the sensor is studied. The Z-directional fibre-fibre bond strength experiments have been performed successfully for unrefined and refined bleached softwood Kraft pulp fibres. Besides, paper scientists are interested in microfibril angle changes during and after application of the Z-directional force. Indeed, there is interest in simultaneous measurement of microfibril angle and mechanical properties such as Z-directional bond strength. To address this need, a microfibril angle measurements system based on microscopic transmission ellipsometry is developed and integrated to the microrobotic platform. The results from both Z-directional bond strength and microfibril angle measurement are promising. In summary, the first concept for simultaneous measurement of microfibril angle and mechanical properties such as Z-directional bond strength at the individual fibre level is developed during this thesis work which has a high practical impact on the fibre characterization research field

Microdevices and Microsystems for Cell Manipulation

Microfabricated devices and systems capable of micromanipulation are well-suited for the manipulation of cells. These technologies are capable of a variety of functions, including cell trapping, cell sorting, cell culturing, and cell surgery, often at single-cell or sub-cellular resolution. These functionalities are achieved through a variety of mechanisms, including mechanical, electrical, magnetic, optical, and thermal forces. The operations that these microdevices and microsystems enable are relevant to many areas of biomedical research, including tissue engineering, cellular therapeutics, drug discovery, and diagnostics. This Special Issue will highlight recent advances in the field of cellular manipulation. Technologies capable of parallel single-cell manipulation are of special interest

International Workshop on MicroFactories (IWMF 2012): 17th-20th June 2012 Tampere Hall Tampere, Finland

This Workshop provides a forum for researchers and practitioners in industry working on the diverse issues of micro and desktop factories, as well as technologies and processes applicable for micro and desktop factories. Micro and desktop factories decrease the need of factory floor space, and reduce energy consumption and improve material and resource utilization thus strongly supporting the new sustainable manufacturing paradigm. They can be seen also as a proper solution to point-of-need manufacturing of customized and personalized products near the point of need

Affordable flexible hybrid manipulator for miniaturised product assembly

Miniaturised assembly systems are capable of assembling parts of a few millimetres in size with an accuracy of a few micrometres. Reducing the size and the cost of such a system while increasing its flexibility and accuracy is a challenging issue. The introduction of hybrid manipulation, also called coarse/fine manipulation, within an assembly system is the solution investigated in this thesis. A micro-motion stage (MMS) is designed to be used as the fine positioning mechanism of the hybrid assembly system. MMSs often integrate compliant micro-motion stages (CMMSs) to achieve higher performances than the conventional MMSs. CMMSs are mechanisms that transmit an output force and displacement through the deformation of their structure. Although widely studied, the design and modelling techniques of these mechanisms still need to be improved and simplified. Firstly, the linear modelling of CMMSs is evaluated and two polymer prototypes are fabricated and characterised. It is found that polymer based designs have a low fabrication cost but not suitable for construction of a micro-assembly system. A simplified nonlinear model is then derived and integrated within an analytical model, allowing for the full characterisation of the CMMS in terms of stiffness and range of motion. An aluminium CMMS is fabricated based on the optimisation results from the analytical model and is integrated within an MMS. The MMS is controlled using dual-range positioning to achieve a low-cost positioning accuracy better than 2µm within a workspace of 4.4×4.4mm2. Finally, a hybrid manipulator is designed to assemble mobile-phone cameras and sensors automatically. A conventional robot manipulator is used to pick and place the parts in coarse mode while the aluminium CMMS based MMS is used for fine alignment of the parts. A high-resolution vision system is used to locate the parts on the substrate and to measure the relative position of the manipulator above MMS using a calibration grid with square patterns. The overall placement accuracy of the assembly system is ±24µm at 3σ and can reach 2µm, for a total cost of less than £50k, thus demonstrating the suitability of hybrid manipulation for desktop-size miniaturised assembly systems. The precision of the existing system could be significantly improved by making the manipulator stiffer (i.e. preloaded bearings…) and adjustable to compensate for misalignment. Further improvement could also be made on the calibration of the vision system. The system could be either scaled up or down using the same architecture while adapting the controllers to the scale.Engineering and Physical Sciences Research Council (EPSRC

Micro Electromechanical Systems (MEMS) Based Microfluidic Devices for Biomedical Applications

Micro Electromechanical Systems (MEMS) based microfluidic devices have gained popularity in biomedicine field over the last few years. In this paper, a comprehensive overview of microfluidic devices such as micropumps and microneedles has been presented for biomedical applications. The aim of this paper is to present the major features and issues related to micropumps and microneedles, e.g., working principles, actuation methods, fabrication techniques, construction, performance parameters, failure analysis, testing, safety issues, applications, commercialization issues and future prospects. Based on the actuation mechanisms, the micropumps are classified into two main types, i.e., mechanical and non-mechanical micropumps. Microneedles can be categorized according to their structure, fabrication process, material, overall shape, tip shape, size, array density and application. The presented literature review on micropumps and microneedles will provide comprehensive information for researchers working on design and development of microfluidic devices for biomedical applications

Scalability study for robotic hand platform

The goal of this thesis project was to determine the lower limit of scale for the RIT robotic grasping hand. This was accomplished using a combination of computer simulation and experimental studies. A force analysis was conducted to determine the size of air muscles required to achieve appropriate contact forces at a smaller scale. Input variables, such as the actuation force and tendon return force, were determined experimentally. A dynamic computer model of the hand system was then created using Recurdyn. This was used to predict the contact (grasping) force of the fingers at full-scale, half-scale, and quarter-scale. Correlation between the computer model and physical testing was achieved for both a life-size and half-scale finger assembly. To further demonstrate the scalability of the hand design, both half and quarter-scale robotic hand rapid prototype assemblies were built using 3D printing techniques. This thesis work identified the point where further miniaturization would require a change in the manufacturing process to micro-fabrication. Several techniques were compared as potential methods for making a production intent quarter-scale robotic hand. Investment casting, Swiss machining, and Selective Laser Sintering were the manufacturing techniques considered. A quarter-scale robotic hand tested the limits of each technology. Below this scale, micro-machining would be required. The break point for the current actuation method, air muscles, was also explored. Below the quarter-scale, an alternative actuation method would also be required. Electroactive Polymers were discussed as an option for the micro-scale. In summary, a dynamic model of the RIT robotic grasping hand was created and validated as scalable at full and half-scales. The model was then used to predict finger contact forces at the quarter-scale. The quarter-scale was identified as the break point in terms of the current RIT robotic grasping hand based on both manufacturing and actuation. A novel, prototype quarter-scale robotic hand assembly was successfully built by an additive manufacturing process, a high resolution 3D printer. However, further miniaturization would require alternate manufacturing techniques and actuation mechanisms

Development of an expert system for supporting the selection of robot grippers

The aim of this thesis is to lay the basis for the development of an expert system for the selection of robot grippers. This work has started with a review of the literature of the grasping principles, of releasing strategies and of the main problems concerning the automatic assembly or, more in general, the handling. Later, we have studied a set of parameters constituting the input of the expert system, together with a set of rules aimed at choosing the appropriate gripper. The work ends with a series of tests, with a focus on the food industry, reporting the results and discussing the possibility of future developments

Virtual reality training for micro-robotic cell injection

This research was carried out to fill the gap within existing knowledge on the approaches to supplement the training for micro-robotic cell injection procedure by utilising virtual reality and haptic technologies