High-Precision Control of Ball-Screw-Driven Stage Based on Repetitive Control Using n-Times Learning Filter

Abstract-This paper presents a novel learning control method for ball-screw-driven stages. In recent years, many types of friction models that are based on complicated equations have been studied. However, it is difficult to treat friction models with equations because the level of precision that is associated with real friction characteristics and parameter tuning are difficult to achieve. In contrast, repetitive perfect tracking control (RPTC) is a repetitive control technique that achieves high-precision positioning. In this paper, we propose the use of RPTC with n-times learning filter. The n-times learning filter has a sharper rolloff property than conventional learning filters. With the use of the n-times learning filter, the proposed RPTC can converge tracking errors n times faster than the RPTC with the conventional learning filter. Simulations and experiments with a ball-screw-driven stage show the fast convergence of the proposed RPTC. Finally, the proposed learning control scheme is combined with data-based friction compensation, and the effectiveness of this combination is verified for the x-y stage of a numerically controlled machine tool. Index Terms-n-times learning, perfect tracking control, repetitive control, zero-phase low-phase filter

Fixtureless automated incremental sheet metal forming

Die-based forming is a technology used by many industries to form metal panels. However, this method of forming lacks flexibility and cost effectiveness. In such cases, manual panel beating is typically undertaken for incremental forming of metal panels. Manual panel forming is a highly skilled operation with very little documentation and is disappearing due to non-observance and a lack of interest. Confederation of British Metal forming (CBM) and Institution of Sheet Metal Engineering (ISME) have realised the need for capturing and understanding manual skills used by panel beaters to preserve the knowledge. At the same time, industries seek for alternative panel forming solutions to produce high quality and cost-effective parts at low volume and reduce the repetitive, yet adaptive parts of the panel forming process to free up skilled workers to concentrate on the forming activities that are more difficult to automate. Incremental forming technologies, currently in practice, lack adaptability as they require substantial fixtures and dedicated tools. In this research a new proof-of-concept fixtureless automated sheet metal forming approach was developed on the basis of human skills captured from panel beaters. The proposed novel approach, named Mechatroforming®, consists of integrated mechanisms to form simple sheet metal parts by manipulating the workpiece using a robotic arm under a repetitive hammering tool. Predictive motion planning based on FEA was analysed and the manual forming skills were captured using a motion capture system. This facilitated the coordinated hammering and motion of the part to produce the intended shape accurately. A 3D measurement system with a vertical resolution of 50μm was also deployed to monitor the formation of the parts and make corrections to the forming path if needed. Therefore, the developed mechatronic system is highly adjustable by robotic motion and was closed loop via the 3D measurement system. The developed automated system has been tested rigorously, initially for bowl shape parts to prove the principle. The developed system which is 98% repeatable for depth and diameter, is able to produce targeted bowl shape parts with ±1% dimensional accuracy, high surface quality, and uniform material thickness of 0.95mm when tested with aluminium. It is envisaged that by further research, the proposed approach can be extended to form irregular and more complicated shapes that are highly in demand in various industries

Robotics 2010

Without a doubt, robotics has made an incredible progress over the last decades. The vision of developing, designing and creating technical systems that help humans to achieve hard and complex tasks, has intelligently led to an incredible variety of solutions. There are barely technical fields that could exhibit more interdisciplinary interconnections like robotics. This fact is generated by highly complex challenges imposed by robotic systems, especially the requirement on intelligent and autonomous operation. This book tries to give an insight into the evolutionary process that takes place in robotics. It provides articles covering a wide range of this exciting area. The progress of technical challenges and concepts may illuminate the relationship between developments that seem to be completely different at first sight. The robotics remains an exciting scientific and engineering field. The community looks optimistically ahead and also looks forward for the future challenges and new development

Advances in High-Speed Atomic Force Microscopy

High-speed atomic force microscopy (HS-AFM) is a scanning probe technique capable of recording processes at the nanometre scale in real time. By sequentially increasing the speed of individual microscope components, images of surfaces can be recorded at up to several images per second. We present a HS-AFM platform composed of custom¿built measurement head, controller and software, scanners and amplifiers that is shared with the community in an open¿hardware fashion. A new scanner design combined with an advanced control system is shown. The simple addition of a secondary actuator to widely available tube scanners increases the scan speed by over an order of magnitude while allowing for a 130 ¿m × 130 ¿m wide field of view, which is not possible with traditional high¿speed scanner designs. Controllers beyond standard proportional-integral controllers are capable of significantly increasing imaging speed by anticipating resonances. Such filters are cumbersome to design with conventional methods. It is shown how convex optimization can be used to design optimal controllers with guaranteed stability for atomic force microscopy in an automated fashion. By integrating two lasers into the small spot¿size optics of an AFM readout head we are able to use the first laser for detecting the deflection of the smallest, and thus fastest currently available high¿speed cantilevers, while using the second for photo¿thermal actuation. Using this instrument, we demonstrate multi¿frequency atomic force microscopy (MF-AFM) at previously not accessible frequencies of more than 20 MHz. By employing the driving laser not for resonant excitation as is usual in dynamic AFM, a new imaging mode, photothermal off-resonance tapping (PORT) is presented. By repeatedly thermally bending the cantilever below it¿s resonant frequency, the surface is probed at a rapid rate. The resulting force is extracted from the deflection of the cantilever in time¿ domain at real time and used for feedback and image generation. The dynamic and static force contributions in both PORT and state of the art high-speed amplitude modulation atomic force microscopy (AM-AFM) are measured and analyzed in detail. It is shown that by decoupling the driving frequency from the resonant frequency the dynamic tip¿sample impact forces can be drastically reduced when compared to resonance based AFM modes. SAS-6 is a centriolar scaffolding protein with a crucial role in the duplication of centrioles, which are the main microtubule organizing organelle of eukaryotic cells. Defects in centriole duplication are associated with cancer and microencephaly. To understand these defects, is therefore important to understand the kinetics of SAS-6. In¿vitro, SAS-6 polymerizes into rings of between eight and ten monomers. Using the new PORT mode we are able to study the dynamic assembly of SAS-6. It is shown how SAS-6 rings can not only assemble by canonical one-by-one addition, but can form as a fusion of larger, already assembled fragments. Finally, it is shown how PORT can be used to observe fast processes of and on living cells. The adhesion and detachment of thrombocyte cells is studied. Membrane disruptive effects are shown on gram¿negative as well as gram¿positive bacteria

Energy-Optimal Control of Over-Actuated Systems - with Application to a Hybrid Feed Drive

Over-actuated (or input-redundant) systems are characterized by the use of more actuators than the degrees of freedom to be controlled. They are widely used in modern mechanical systems to satisfy various control requirements, such as precision, motion range, fault tolerance, and energy efficiency. This thesis is particularly motivated by an over-actuated hybrid feed drive (HFD) which combines two complementary actuators with the aim to reduce energy consumption without sacrificing positioning accuracy in precision manufacturing. This work addresses the control challenges in achieving energy optimality without sacrificing control performance in so-called weakly input-redundant systems, which characterize the HFD and most other over-actuated systems used in practice. Using calculus of variations, an optimal control ratio/subspace is derived to specify the optimal relationship among the redundant actuators irrespective of external disturbances, leading to a new technique termed optimal control subspace-based (OCS) control allocation. It is shown that the optimal control ratio/subspace is non-causal; accordingly, a causal approximation is proposed and employed in energy-efficient structured controller design for the HFD. Moreover, the concept of control proxy is proposed as an accurate causal measurement of the deviation from the optimal control ratio/subspace. The proxy enables control allocation for weakly redundant systems to be converted into regulation problems, which can be tackled using standard controller design methodologies. Compared to an existing allocation technique, proxy-based control allocation is shown to dynamically allocate control efforts optimally without sacrificing control performance. The relationship between the proposed OCS control allocation and the traditional linear quadratic control approach is discussed for weakly input redundant systems. The two approaches are shown to be equivalent given perfect knowledge of disturbances; however, the OCS control allocation approach is shown to be more desirable for practical applications like the HFD, where disturbances are typically unknown. The OCS control allocation approach is validated in simulations and machining experiments on the HFD; significant reductions in control energy without sacrificing positioning accuracy are achieved.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146104/1/molong_1.pd

Assistive Guitar Plucking Device and User Interface

The goal of the project was to develop a wireless, battery-powered device with a plucking mechanism and a wearable user interface (UI) that would enable individuals with physical disabilities to play a guitar. The plucking mechanism, mounted to an adjustable frame around the guitar, has 3D printed plectra to actuate each guitar string. The inertial measurement unit based UI is comprised of two wearable devices that calculate which strings to pluck, by using sensor fusion to track user motion and device orientation. Music provides people an avenue to express their emotions and has been shown to stimulate the brain in uniquely beneficial ways. This project provides an opportunity to create music for individuals who have not previously had access to this experience

Developing tools and methods for object-oriented mechatronics

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. [161]-166).The digital revolution has fundamentally changed our lives by giving us new ways to express ourselves through digital media. For example, accessible multimedia content creation tools allow people to instantiate their ideas and share them easily. However, most of these outcomes only exist on-screen and online. Despite the growing accessibility of digital design and fabrication tools the physical world and everyday objects surrounding us have been largely excluded from a parallel explosion of possibilities to express ourselves. Increasingly, webbased services allow professional and non-professional audiences to access computer-aided manufacturing (CAM) tools like 3D-printing and laser-cutting. Nonetheless, there are few (if any) design tools and methods for creating complex mechanical assemblies that take full advantage of CAM systems. Creating unique mechatronic artifacts or "originalMachines" requires more specific and sophisticated design tools than exist today. "Object-Oriented Mechatronics" is a parametric design approach that connects knowledge about mechanical assemblies and electronics with the requirements of digital manufacturing processes. Parametric instances like gears, bearing and servos are made available as objects within a CAD environment which can then be implemented into specific projects. The approach addresses the missing link between accessible rapid-manufacturing services and currently available design tools thereby creating new opportunities for self-expression through mechatronic objects and machines. The dissertation matches mechanical components and assemblies with rapid manufacturing methods by exploring transferability of conventional manufacturing techniques to appropriate rapid manufacturing tools. I rebuild various gearing and bearing principles like four-contact point bearings, cross roller bearings, spur and helical gears, planetary gears, cycloidal and harmonic gear reducers using the laser cutter, the CNC-mill and the 3D-printer. These explorations lead to more complex assemblies such as the PlywoodServo, 3DprintedClock and 3-DoF (Degree of Freedom) Head. The lessons from these explorations are summarized in a detailed "cook book" of novel mechatronic assemblies enabled by new fabrication tools. Furthermore, I use the results to develop a CAD tool that brings together several existing software packages and plug-ins including Rhino, Grasshopper and the Firefly experiments for Arduino, which will allow animation, fabrication and control of original machines. The tool is an example of an object-oriented design approach to mechatronic assemblies. A user calls a DoF (Degree of Freedom) object (parametric servo) with specific parameters like gearing and bearing types, motor options and control and communication capabilities. The DoF object then creates the corresponding geometry which can be connected and integrated with other actuators and forms. A group of roboticists and designers participated in a workshop to test the tool and make proposals for original machines using the tool. The dissertation has contributions on multiple levels. First, the actuator assembly examples and parametric design tool present a body of novel work that illustrates the benefits of going beyond off-the-shelf actuator assemblies and kit-of-parts for robotic objects. Second, this tool and the accompanying examples enable the design of more original machines with custom actuator assemblies using the latest digital fabrication tools. Finally, these explorations illustrate how new CAD/ CAM tools can facilitate an exchange between more design-oriented users and more engineering-oriented users.by Peter Schmitt.Ph.D

The 20th Aerospace Mechanisms Symposium

Numerous topics related to aerospace mechanisms were discussed. Deployable structures, electromagnetic devices, tribology, hydraulic actuators, positioning mechanisms, electric motors, communication satellite instruments, redundancy, lubricants, bearings, space stations, rotating joints, and teleoperators are among the topics covered

Dynamics and Control of Flexure-based Large Range Nanopositioning Systems.

The objective of this thesis is to demonstrate desktop-size and cost-effective flexure-based multi-axis nanopositioning capability over a motion range of several millimeters per axis. Increasing the motion range will overcome one of the main drawbacks of existing nanopositioning systems, thereby significantly improving the coverage area in nanometrology and nanomanufacturing applications. A single-axis nanopositioning system, comprising a symmetric double parallelogram flexure bearing and a traditional-architecture moving magnet actuator, is designed, fabricated, and tested. A figure of merit for the actuator is derived and shown to directly impact the system-level trade-offs in terms of range, resolution, bandwidth, and temperature rise. While linear feedback controllers provide good positioning performance for point-to-point commands, the tracking error for dynamic commands prove to be inadequate due to the nonlinearities in the actuator and its driver. To overcome this, an iterative learning controller is implemented in conjunction with linear feedback to reduce the periodic component of the tracking error by more than two orders of magnitude. Experimental results demonstrate 10 nm RMS tracking error over 8 mm motion range in response to a 2 Hz bandlimited triangular command. For the XY nanopositioning system, a lumped-parameter model of an existing XY flexure bearing is developed in order to understand the unexplained variation observed in the transfer function zeros over the operating range of motion. It is shown that the kinematic coupling, due to geometric nonlinearities in the beam mechanics, and small dimensional asymmetry, due to manufacturing tolerances, may conspire to produce complex-conjugate nonminimum phase zeros at certain operating points in the system's workspace. This phenomenon significantly restricts the overall performance of the feedback control system. After intentional use of large asymmetry is employed to overcome this problem, independent feedback and iterative learning controllers are implemented along each axis. Experimental results demonstrate 20 nm RMS radial tracking error while traversing a 2 mm diameter circle at 2 Hz.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107086/1/parmar_1.pd

Humanoid Robots

For many years, the human being has been trying, in all ways, to recreate the complex mechanisms that form the human body. Such task is extremely complicated and the results are not totally satisfactory. However, with increasing technological advances based on theoretical and experimental researches, man gets, in a way, to copy or to imitate some systems of the human body. These researches not only intended to create humanoid robots, great part of them constituting autonomous systems, but also, in some way, to offer a higher knowledge of the systems that form the human body, objectifying possible applications in the technology of rehabilitation of human beings, gathering in a whole studies related not only to Robotics, but also to Biomechanics, Biomimmetics, Cybernetics, among other areas. This book presents a series of researches inspired by this ideal, carried through by various researchers worldwide, looking for to analyze and to discuss diverse subjects related to humanoid robots. The presented contributions explore aspects about robotic hands, learning, language, vision and locomotion