Human-friendly robotic manipulators: safety and performance issues in controller design

Recent advances in robotics have spurred its adoption into new application areas such as medical, rescue, transportation, logistics, personal care and entertainment. In the personal care domain, robots are expected to operate in human-present environments and provide non-critical assistance. Successful and flourishing deployment of such robots present different opportunities as well as challenges. Under a national research project, Bobbie, this dissertation analyzes challenges associated with these robots and proposes solutions for identified problems. The thesis begins by highlighting the important safety concern and presenting a comprehensive overview of safety issues in a typical domestic robot system. By using functional safety concept, the overall safety of the complex robotic system was analyzed through subsystem level safety issues. Safety regions in the world model of the perception subsystem, dependable understanding of the unstructured environment via fusion of sensory subsystems, lightweight and compliant design of mechanical components, passivity based control system and quantitative metrics used to assert safety are some important points discussed in the safety review. The main research focus of this work is on controller design of robotic manipulators against two conflicting requirements: motion performance and safety. Human-friendly manipulators used on domestic robots exhibit a lightweight design and demand a stable operation with a compliant behavior injected via a passivity based impedance controller. Effective motion based manipulation using such a controller requires a highly stiff behavior while important safety requirements are achieved with compliant behaviors. On the basis of this intuitive observation, this research identifies suitable metrics to identify the appropriate impedance for a given performance and safety requirement. This thesis also introduces a domestic robot design that adopts a modular design approach to minimize complexity, cost and development time. On the basis of functional modularity concept where each module has a unique functional contribution in the system, the robot “Bobbie-UT‿ is built as an interconnection of interchangeable mobile platform, torso, robotic arm and humanoid head components. Implementation of necessary functional and safety requirements, design of interfaces and development of suitable software architecture are also discussed with the design

Toward a Variable Stiffness Surgical Manipulator Based on Fiber Jamming Transition

Soft robots have proved to represent a new frontier for the development of intelligent machines able to show new capabilities that can complement those currently performed by robots based on rigid materials. One of the main application areas where this shift is promising an impact is minimally invasive surgery. In previous works, the STFF-FLOP soft manipulator has been introduced as a new concept of using soft materials to develop endoscopic tools. In this paper, we present a novel kind of stiffening system based on fiber jamming transition that can be embedded in the manipulator to widen its applicability by increasing its stability and with the possibility to produce and transmit higher forces. The STIFF-FLOP original module has been re-designed in two new versions to incorporate the variable stiffness mechanism. The two designs have been evaluated in terms of dexterity and variable stiffness capability and, despite a general optimization rule did not clearly emerge, the study confirmed that fiber jamming transition can be considered an effective technological approach for obtaining variable stiffness in slender soft structures

Workshop on "Robotic assembly of 3D MEMS".

Proceedings of a workshop proposed in IEEE IROS'2007.The increase of MEMS' functionalities often requires the integration of various technologies used for mechanical, optical and electronic subsystems in order to achieve a unique system. These different technologies have usually process incompatibilities and the whole microsystem can not be obtained monolithically and then requires microassembly steps. Microassembly of MEMS based on micrometric components is one of the most promising approaches to achieve high-performance MEMS. Moreover, microassembly also permits to develop suitable MEMS packaging as well as 3D components although microfabrication technologies are usually able to create 2D and "2.5D" components. The study of microassembly methods is consequently a high stake for MEMS technologies growth. Two approaches are currently developped for microassembly: self-assembly and robotic microassembly. In the first one, the assembly is highly parallel but the efficiency and the flexibility still stay low. The robotic approach has the potential to reach precise and reliable assembly with high flexibility. The proposed workshop focuses on this second approach and will take a bearing of the corresponding microrobotic issues. Beyond the microfabrication technologies, performing MEMS microassembly requires, micromanipulation strategies, microworld dynamics and attachment technologies. The design and the fabrication of the microrobot end-effectors as well as the assembled micro-parts require the use of microfabrication technologies. Moreover new micromanipulation strategies are necessary to handle and position micro-parts with sufficiently high accuracy during assembly. The dynamic behaviour of micrometric objects has also to be studied and controlled. Finally, after positioning the micro-part, attachment technologies are necessary

Vitreo-retinal eye surgery robot : sustainable precision

Vitreo-retinal eye surgery encompasses the surgical procedures performed on the vitreous humor and the retina. A procedure typically consists of the removal of the vitreous humor, the peeling of a membrane and/or the repair of a retinal detachment. Vitreo-retinal surgery is performed minimal invasively. Small needle shaped instruments are inserted into the eye. Instruments are manipulated by hand in four degrees of freedom about the insertion point. Two rotations move the instrument tip laterally, in addition to a translation in axial instrument direction and a rotation about its longitudinal axis. The manipulation of the instrument tip, e.g. a gripping motion can be considered as a fifth degree of freedom. While performing vitreo-retinal surgery manually, the surgeon faces various challenges. Typically, delicate micrometer range thick tissue is operated, for which steady hand movements and high accuracy instrument manipulation are required. Lateral instrument movements are inverted by the pivoting insertion point and scaled depending on the instrument insertion depth. A maximum of two instruments can be used simultaneously. There is nearly no perception of surgical forces, since most forces are below the human detection limit. Therefore, the surgeon relies only on visual feedback, obtained via a microscope or endoscope. Both vision systems force the surgeon to work in a static and non ergonomic body posture. Although the surgeon’s proficiency improves throughout his career, hand tremor will become a problem at higher age. Robotically assisted surgery with a master-slave system can assist the surgeon in these challenges. The slave system performs the actual surgery, by means of instrument manipulators which handle the instruments. The surgeon remains in control of the instruments by operating haptic interfaces via a master. Using electronic hardware and control software, the master and slave are connected. Amongst others, advantages as tremor filtering, up-scaled force feedback, down-scaled motions and stabilized instrument positioning will enhance dexterity on surgical tasks. Furthermore, providing the surgeon an ergonomic body posture will prolong the surgeon’s career. This thesis focuses on the design and realization of a high precision slave system for eye surgery. The master-slave system uses a table mounted design, where the system is compact, lightweight, easy to setup and equipped to perform a complete intervention. The slave system consists of two main parts: the instrument manipulators and their passive support system. Requirements are derived from manual eye surgery, conversations with medical specialists and analysis of the human anatomy and vitreo-retinal interventions. The passive support system provides a stiff connection between the instrument manipulator, patient and surgical table. Given the human anatomical diversity, presurgical adjustments can be made to allow the instrument manipulators to be positioned over each eye. Most of the support system is integrated within the patient’s headrest. On either the left or right side, two exchangeable manipulator-support arms can be installed onto the support system, depending on the eye being operated upon. The compact, lightweight and easy to install design, allows for a short setup time and quick removal in case of a complication. The slave system’s surgical reach is optimized to emulate manually performed surgery. For bimanual instrument operation, two instrument manipulators are used. Additional instrument manipulators can be used for non-active tools e.g. an illumination probe or an endoscope. An instrument manipulator allows the same degrees of freedom and a similar reach as manually performed surgery. Instrument forces are measured to supply force feedback to the surgeon via haptic interfaces. The instrument manipulator is designed for high stiffness, is play free and has low friction to allow tissue manipulation with high accuracy. Each instrument manipulator is equipped with an on board instrument change system, by which instruments can be changed in a fast and secure way. A compact design near the instrument allows easy access to the surgical area, leaving room for the microscope and peripheral equipment. The acceptance of a surgical robot for eye surgery mostly relies on equipment safety and reliability. The design of the slave system features various safety measures, e.g. a quick release mechanism for the instrument manipulator and additional locks on the pre-surgical adjustment fixation clamp. Additional safety measures are proposed, like a hard cover over the instrument manipulator and redundant control loops in the controlling FPGA. A method to fixate the patient’s head to the headrest by use of a custom shaped polymer mask is proposed. Two instrument manipulators and their passive support system have been realized so far, and the first experimental results confirm the designed low actuation torque and high precision performance

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

User needs, benefits and integration of robotic systems in a space station laboratory

The methodology, results and conclusions of the User Needs, Benefits, and Integration Study (UNBIS) of Robotic Systems in the Space Station Microgravity and Materials Processing Facility are summarized. Study goals include the determination of user requirements for robotics within the Space Station, United States Laboratory. Three experiments were selected to determine user needs and to allow detailed investigation of microgravity requirements. A NASTRAN analysis of Space Station response to robotic disturbances, and acceleration measurement of a standard industrial robot (Intelledex Model 660) resulted in selection of two ranges of low gravity manipulation: Level 1 (10-3 to 10-5 G at greater than 1 Hz.) and Level 2 (less than = 10-6 G at 0.1 Hz). This included an evaluation of microstepping methods for controlling stepper motors and concluded that an industrial robot actuator can perform milli-G motion without modification. Relative merits of end-effectors and manipulators were studied in order to determine their ability to perform a range of tasks related to the three low gravity experiments. An Effectivity Rating was established for evaluating these robotic system capabilities. Preliminary interface requirements were determined such that definition of requirements for an orbital flight demonstration experiment may be established

Concept of Modular Kinematics to Design Ultra-high Precision Parallel Robots

Miniaturisation will be the key challenge for the next decade in numerous industrial fields, such as microelectronics, optics and biomedical engineering. Although most of their products already achieve footprints of some square millimeters, the trend towards the integration of a maximum number of elements in a minimal volume requires even more compact components. This tendency creates a growing need for industrial robots able to perform micromanipulation and microassembly tasks with a submicrometric precision. Nonetheless, the design of such machines is nowadays costly, both in time and money, mostly because of the twofold complexity of their development: first, from a kinematic standpoint, the use of a parallel structure consists in a particularly interesting approach to build ultra-high precision robots. However, the synthesis of such a kinematics proves especially challenging for machines presenting more than 3 degrees of freedom. Moreover, the resulting robots are scarcely flexible: if the industrial specifications are modified, which for example necessitates to add a degree of freedom or to change the position of a rotation centre, the design process has to be restarted, often from the very beginning. The second challenge consists in the mechanical design of flexure-based mechanisms: flexure hinges are joints which are based on the elasticity of the matter. They allow to perform motions which are without friction, backlash and wear; their use is thus mandatory to achieve the aimed submicrometric precision. Albeit the synthesis of planar and low-degree of freedom structures is now widely investigated, the development of a whole tridimensional flexure-based robot is still infrequent, especially in the industrial context. This thesis thus introduces a modular design methodology which significantly reduces the time-to-market of ultra-high precision robots. This procedure can be compared to a robotic Lego, where a finite number of conceptual building bricks allows to easily design and modify parallel robots. Furthermore, this work shows that the machines resulting from this approach present similar or even improved performances compared to robots developed more traditionally. The key aspect of this thesis consists in the concept of modular kinematics, which aims at facilitating the synthesis of parallel kinematics thanks to solution catalogues. At this step of the methodology, the conceptual building bricks and the kinematics are totally independent from any mechanical design: they can thus be used to synthesise a large variety of robots, from machine-tools to microscale robots. An exhaustive conceptual solution catalogue groups all kinematics generated by the combination of the building bricks. Then, a reduced solution catalogue for ultra-high precision is proposed: based on selection criteria linked with the design and machining of flexure-based mechanisms, it allows to reduce the total number of solutions and thus facilitates the practical use of the concept. The second part of this work details the mechanical design of the building bricks, whose main challenge consists in increasing the ratio between the working ranges of the mechanisms and their overall size. One or more flexure-based solutions have been developed for each motorised brick: a special emphasis is given to the original use of a Remote Centre of Motion, which allows to achieve high rotation angles while drastically reducing parasitic translations. The development of a standardised actuation sub-brick, common to all motorised bricks, introduces a new level of modularity, thus increasing even more the flexibility of the methodology. As for non-actuated bricks, original designs and uncommon uses of well-known mechanisms are proposed. A case study on a 5-degree of freedom robot, Legolas 5, finally illustrates the practical use of the methodology: first, the selection in the solution catalogue of a kinematics adapted to the specifications of the robot is detailed. Then, the development of the Legolas 5 prototype highlights the mechanical design of the necessary building bricks, as well as assembly subtleties, such as force alignment and gravity compensation, which allow to shrewdly design a high-performance robot. The measurements of this machine have shown motion resolution and repeatability of 50 nm in translation and 1.9 µrad in rotation (limited by the sensor resolution). This case study has generated the Legolas family, a new family of ultra-high precision parallel robots, which notably includes the orthogonal version of the Delta kinematics: using only 6 of the conceptual building bricks, one solution can be built for each of the 19 possible robot mobilities. The promising characterisation of the Legolas 5 tends to suggest that the robots from this family will be interesting candidates to fulfill the upcoming need for quickly designed and high-performance industrial ultra-high precision machines