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George W. Woodruff School of Mechanical Engineering

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https://hdl.handle.net/1853/70728

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College of Engineering

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Advanced Mechanical Bipedal Experimental Robotics Lab

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Computational Reactor and Medical Physics Laboratory

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Cryo Lab

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Environmentally Conscious Design and Manufacturing

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Fusion Research Center

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Publication Search Results

Now showing 1 - 10 of 36

Admittance and impedance haptic control for realization of digital clay as an effective human machine interface (HMI) device

(Georgia Institute of Technology, 2009-11-17) Ngoo, Cheng Shu

Shape plays an important role in our everyday life to interpret information about the surroundings whether we are aware or not. Together with visual and auditory information, we are able to obtain and process information for different purposes. Output devices such as monitors and speakers convey visual and auditory information while input devices such as touch screen and microphones receive that information for human machine interaction. Such devices have become commonplace but there has yet to be a fitting input/output device utilizing our haptic perception. Digital Clay is a next generation Human Machine Interface (HMI) device for 2.5D shape input/output via an array of hydraulic actuators. This device potentially has wide applications in the areas of engineering, sciences, medicine, military, entertainment etc. The user can perceive the shape of a computer programmed model in a tangible and concrete manner which means an added realism with the addition of the sense of touch. Conversely, the user can also use Digital Clay as an input device to the computer, by shaping and molding desired shapes on the device, no longer limited to drawing models with a mouse on CAD software. Shape display has been achieved with the current 5x5 prototype at the Georgia Institute of Technology but this research seeks to expand its capability to include haptic feedback and consequently shaping mode. This thesis gives an overview of the current 5x5 prototype and implements 2 commonly used haptic control methods, the admittance control and the impedance control. For implementing the admittance control, actuator displacement and velocity controllers and a proportional integral observer (PIO) are designed. The model-based unknown input observer is a solution for force estimation without added sensors in the actuators. For implementing the impedance control, a novel pressure control technique is designed to provide pressure feedback to the actuators array along with accurate and reliable displacement measurement. Both of the haptic control methods are evaluated, hardware and software limitations are outlined and possible future improvements are suggested.
An efficient haptic interface for a variable displacement pump controlled excavator

(Georgia Institute of Technology, 2009-05) Elton, Mark David

Human-machine interfaces influence both operator effectiveness and machine efficiency. Further immersion of the operator into the machine’s working environment gives the operator a better feel for the status of the machine and its working conditions. With this knowledge, operators can more efficiently control machines. The use of multi-modal HMIs involving haptics, sound, and visual feedback can immerse the operator into the machine’s environment and provide assistive clues about the state of the machine. This thesis develops a realistic excavator model that mimics a mini-excavator’s dynamics and soil interaction during digging tasks. A realistic graphical interface is written that exceeds the quality of current academic simulators. The graphical interface and new HMI are placed together with a model of the excavator’s mechanical and hydraulic dynamics into an operator workstation. Two coordinated control schemes are developed on an haptic display for a mini-excavator and preliminary tests are run to measure increases in operator effectiveness and machine efficiency.
Fabric control for feeding into an automated sewing machine

(Georgia Institute of Technology, 2009-03-25) Winck, Ryder Christian

The importance of automating the garment manufacturing process has been understood since the early 1980s. However, in spite of millions of dollars spent on research, three decades later, the industry is still far from achieving a fully autonomous process. Previous work on fabric control in automated sewing focused on the control of only a single sheet of fabric using an industrial manipulator with an overhead vision system. These methods did not meet the accuracy and robustness requirements of the sewing process with respect to fabric position and fabric tension. To address these issues, a new method for fabric control in automated sewing is described. It uses the current feed mechanism on sewing machines, feed dogs, but modifies them to be servo-controlled. These servo controlled actuators, servo dogs, individually control two sheets of fabric before the fabric reaches the needle and during the sewing process. The servo dogs actuate the fabric 180o out of phase with the sewing needle, providing incremental control of the fabric when the needle is out of the fabric. To achieve this type of control successfully for automated sewing, the servo dogs have been designed for short displacement, high acceleration motions using a cable drive system powered by voice coil motors. Feedback of fabric position has been determined to be necessary and is to be provided by a thread-tracking vision system. This thesis outlines the general design of the system and discusses a prototype used to validate the design, and describes experiments performed to examine how the fabric will behave with the use of this type of actuation method.
Haptic control and operator-guided gait coordination of a pneumatic hexapedal rescue robot

(Georgia Institute of Technology, 2008-07-10) Guerriero, Brian A.

The Compact Rescue Crawler is a pneumatic legged robot. Two legs of a hexapod were designed and built. The legs are controlled directly from operator inputs. The operator gives foot position inputs through two PHANToM haptic controllers. A PD controller with a supplementary force gain-scheduler control stroke lengths of each cylinder. The force-based position control technique allows the robot feet to track operator inputs to within 10% position error. A guided gait algorithm was developed to allow the operator to control all 6 legs simply by haptically guiding the front two. The operator records successful and collision-free trajectories and the gait coordinator plays the trajectories through the rear legs as they approach the detected obstacles. This hybrid gait algorithm allows the robot to proceed through a hazardous environment, guided by an operator, but without taxing the input capabilities of the human operator.
Robust nonlinear observer for a non-collocated flexible motion system

(Georgia Institute of Technology, 2008-04-01) Waqar, Mohsin

Robustness of the closed-loop system has repercussions on both stability and performance, making the study of robustness very important. Fundamentally, the performance and stability of closed-loop systems utilizing state-feedback are tied to that of the observers. The primary goal of this thesis is to develop a robust nonlinear observer and closely examine the usefulness of the observer in the presence of non-collocation and parametric uncertainty and as an integral component in closed-loop control. The usefulness of the observer being investigated depends on robustness, accuracy, computational burden, tunability, ease of design, and ease of implementation on an actual flexible motion system. The design and subsequent integration of the Kalman filter, an optimal observer, into a closed-loop system is well known and systematic. However, there are shortcomings of the Kalman filter in the presence of model uncertainty which are highlighted in this work. Simulation studies are conducted using the Simulation Module in National Instruments LabVIEW 8.5 and experiments are conducted on a physical system consisting of a single flexible link with non-collocation of actuators and sensors using LabVIEW Real Time 8.5. Simulations serve as a means to analyze the performance of the optimal observer and the robust observer by analyzing their dynamic behavior as well as that of the closed-loop system with each observer in place. The focus of experiments is on investigating implementation of the robust observer, including initialization and tuning of observer design parameters off-line and on-line. Simulations verify the robustness properties of the sliding mode observer while experiments show that the robust observer can be implemented at fast control rates and that replacing the Kalman filter with a robust observer has direct ramifications on closed-loop performance.
Auto-Calibration and Control Applied to Electro-Hydraulic Poppet Valves

(Georgia Institute of Technology, 2007-11-12) Opdenbosch, Patrick

Modern control design is sometimes accompanied by the challenge of dealing with nonlinear systems or plants. In some situations, due to the complexity of the plant and the unavailability of suitable models, the controls engineer opts for developing control schemes based on look-up tables. These tables, typically populated with the steady state inverse input-output characteristics of the plant, are used to compensate the plant via open-loop or closed-loop to solve the control problem. In an effort to present a new alternative, a general theoretical framework for online auto-calibration and control of general nonlinear systems is developed in this dissertation. This technique simultaneously learns the inverse input-state mapping (i.e. the calibration mapping) of the plant while forcing its state to follow a prescribed desired trajectory. The main requirements for the successful application of the novel control law are knowledge of the order of the plant and some generic data to initialize the inverse mapping. This last requirement can be easily fulfilled by using steady-state data or the equilibrium points of the plant. In this approach, the inverse mapping is learned from the current and past states. The learning is accomplished in a composite manner by employing input and state errors. The map is used simultaneously in the feedforward path to control the plant. The performance of the plant subject to this novel controller is validated through simulations and experimental data. The new control method is applied to a novel Electro-Hydraulic Poppet Valve (EHPV). These valves are used in a Wheatstone bridge arrangement for motion control of hydraulic actuators. This is preferred over the conventional use of spool valves due to the energy savings potential. It is shown in this dissertation that this method improves the value of using these types of valves for motion control in hydraulics. This is due to the combination of self-learning (auto-calibration) and better performance for a more efficient operation of hydraulic equipment. Additionally, it is shown that the auto-calibration of the valves can be used for health monitoring of the same, which consequently improves their reliability and expedites maintenance downtime.
Controlling a Passive Haptic Master During Bilateral Teleoperation

(Georgia Institute of Technology, 2007-08-27) Black, Benjamin Andrew

Haptic devices allow a human to interact physically with a remote or virtual environment by providing tactile feedback to the user. In general haptic devices can be classified in two groups according to the energetic nature of their actuators. Devices using electric motors, pneumatic or hydraulic cylinders or other similar actuators that can add energy to the system are considered "active." Devices using brakes, clutches or other passive actuators are considered "passive" haptic devices. The research presented here focuses on the use of passive haptic devices used during teleoperation, the remote control of a "slave" device by the haptic "master" device. An actuation scheme as well as three different control methods is developed for providing the user with haptic feedback. As a final step, the effectiveness of the controllers is compared to that of a commercially available active haptic device. Twenty subjects provide data that shows the usefulness of the passive device in three typical teleoperation tasks.
Haptic Control of Hydraulic Machinery Using Proportional Valves

(Georgia Institute of Technology, 2007-07-30) Kontz, Matthew Edward

Supplying haptic or force feedback to operators using hydraulic machinery such as excavators has the potential to increase operator capabilities. Haptic, robotic, human-machine interfaces enable several enhancing features including coordinated motion control and programmable haptic feedback. Coordinated or resolved motion control supplies a more intuitive means of specifying the equipment's motion. Haptic feedback is used to relay meaningful information back to the user in the form of force signals about digging force acting on the bucket, programmable virtual constraints and system limitations imposed by the mechanism, maximum pressure or maximum flow. In order to make this technology economically viable, the benefits must offset the additional cost associated with implementation. One way to minimize this cost is to not use high-end hydraulic components. For smaller backhoes and mini-excavators this means that the hydraulic systems are comprised of a constant displacement pump and proportional direction control valves. Hydraulic and haptic control techniques suitable for backhoes/excavators are developed and tested on a small backhoe test-bed. A virtual backhoe simulator is created for controller design and human evaluation. Not only is the virtual simulator modeled after the test-bed, but the control algorithm used in the simulator is the same as the actual backhoe test-bed. Data from human subject tests are presented that evaluate the control strategies on both the real and virtual backhoe. The end goal of this project is to incorporate coordinated haptic control algorithms that work with low-cost systems and maximize the enhancement of operator capabilities.
The Development of a Miniature Flexible Flapping Wing Mechanism for use in a Robotic Air Vehicle

(Georgia Institute of Technology, 2007-03-14) Jadhav, Gautam

In this study a mechanism which produced flapping and pitching motions was designed and fabricated. These motions were produced by using a single electric motor and by exploiting flexible structures. The aerodynamic forces generated by flexible membrane wings were measured using a two degree of freedom force balance. This force balance measured the aerodynamic forces of lift and thrust. Two sets of wings with varying flexibility were made. Lift and thrust measurements were acquired as the mechanism flapped the wings in a total of thirteen cases. These thirteen cases consisted of zero velocity free stream conditions as well as forward flight conditions of five meters per second. In addition, flapping frequency was varied from two Hertz to four Hertz, while angle of attack offsets varied from zero degrees to fifteen degrees. The four most interesting conditions for both sets of wings were explored in more detail. For each of these conditions, high-speed video of the flapping wing was taken. The images from the video were also correlated with cycle averaged aerodynamic forces produced by the mechanism. Several observations were made regarding the behavior of flexible flapping wings that should aid in the design of future flexible flapping wing vehicles.
Internet Based Bilateral Teleoperation

(Georgia Institute of Technology, 2006-10-17) Ching, Ho

In conventional bilateral teleoperation, transmission delay over the Internet can potentially cause instability. The wave variable algorithm guarantees stability under varying transmission delay at the cost of poor transient performance. Adding a predictor on the master side can reduce this undesirable side-effect, but that would require a slave model. An inaccurate slave model used in the predictor as well as variations in transmission delay, both of which are likely under realistic situations, can result in steady state errors. A direct drift control algorithm is used to drive this error to zero regardless of the source of error. A semi-adaptive predictor that can distinguish between free space and rigid contact environment is used to provide more accurate force feedback on the master side. A full adaptive predictor is also used that estimates the slave environment parameters using recursive least squares with a forgetting factor. This research presents the experimental results and evaluations of the wave variable based methods under a realistic operation environment using a real master and slave. The effectiveness of this algorithm is fully evaluated using human subjects with no previous experience in haptics. Three algorithms are tested using PHANTOM brand haptic devices as master and slave: conventional bilateral teleoperation with no transmission delay as control, wave variable teleoperation with approximately 200 ms transmission delay one way, and wave variables with adaptive predictor and direct drift control with approximately 200 ms transmission delay one way. For each algorithm the human subjects are asked to perform three simple tasks: use the master to force the slave to track a reference trajectory in free space with the least amount of error, identify a contour surface on the slave side as accurately as possible using only haptic information from the master, and navigate a simple maze on the slave side in the least amount of time using haptic information from the master.