Motor shaft vibrations may have a negative effect on ability to implement a stiff haptic wall

A one degree of freedom experimental test bed is used to investigate the effects of elastic vibration in haptic devices. Strong angular vibration occurs at the motor rotor due to elastic deformation in the shaft. These vibrations occur due to large discontinuities in the virtual environment such as stiff contact which is common in haptics. Also looked at was the effect of these vibrations on stability and control. It was found that the vibrations may negatively affect the stability of the haptic device by introducing large measurement errors to the controller. The experiments investigated using different types of damping in controller feedback. Adding damping to the system whilst these elastic vibrations are present can successfully damp the system, but also tend to increase the magnitude of vibrations sometimes resulting in greater instability. Finally, a second non co-located encoder was used to try to eliminate measurement error from the system due to vibration. It was found that by simply placing the encoder closer to the link where the angle is being measured, error due to rotational flex in the shaft is eliminated. This yielded the greatest improvement in controller performance, nearly eliminating the presence of the vibrations and their effects

Doctor of Philosophy

dissertationIn this dissertation, we present methods for intuitive telemanipulation of manipulators that use piezoelectric stick-slip actuators (PSSAs). Commercial micro/nano-manipulators, which utilize PSSAs to achieve high precision over a large workspace, are typically controlled by a human operator at the joint level, leading to unintuitive and time-consuming telemanipulation. Prior work has considered the use of computer-vision-feedback to close a control loop for improved performance, but computer-vision-feedback is not a viable option for many end users. We discuss how open-loop models of the micro/nano-manipulator can be used to achieve desired end-effector movements, and we explain the process of obtaining open-loop models. We propose a rate-control telemanipulation method that utilizes the obtained model, and we experimentally quantify the effectiveness of the method using a common commercial manipulator (the Kleindiek MM3A). The utility of open-loop control methods for PSSAs with a human in the loop depends directly on the accuracy of the open-loop models of the manipulator. Prior research has shown that modeling of piezoelectric actuators is not a trivial task as they are known to suffer from nonlinearities that degrade their performance. We study the effect of static (non-inertial) loads on a prismatic and a rotary PSSA, and obtain a model relating the step size of the actuator to the load. The actuator-specific parameters of the model are calibrated by taking measurements in specific configurations of the manipulator. Results comparing the obtained model to experimental data are presented. PSSAs have properties that make them desirable over traditional DC-motor actuators for use in retinal surgery. We present a telemanipulation system for retinal surgery that uses a full range of existing disposable instruments. The system uses a PSSA-based manipulator that is compact and light enough that it could reasonably be made head-mounted to passively compensate for head movements. Two mechanisms are presented that enable the system to use existing disposable actuated instruments, and an instrument adapter enables quick-change of instruments during surgery. A custom stylus for a haptic interface enables intuitive and ergonomic telemanipulation of actuated instruments. Experimental results with a force-sensitive phantom eye show that telemanipulated surgery results in reduced forces on the retina compared to manual surgery, and training with the system results in improved performance. Finally, we evaluate operator efficiency with different haptic-interface kinematics for telemanipulated retinal surgery. Surgical procedures of the retina require precise manipulation of instruments inserted through trocars in the sclera. Telemanipulated robotic systems have been developed to improve retinal surgery, but there is not a unique mapping of the motions of the surgeon's hand to the lower-dimensional motions of the instrument through the trocar. We study operator performance during a precision positioning task on a force-sensing phantom retina, reminiscent of telemanipulated retinal surgery, with three common haptic-interface kinematics implemented in software on a PHANTOM Premium 6DOF haptic interface. Results from a study with 12 human subjects show that overall performance is best with the kinematics that represent a compact and inexpensive option, and that subjects' subjective preference agrees with the objective performance results

A Service Robot for Navigation Assistance and Physical Rehabilitation of Seniors

The population of the advanced countries is ageing, with the direct consequence that an increasing number of people will have to live with sensitive, cognitive and physical disabilities. People with impaired physical ability are not confident to move alone, especially in crowded environment and for long journeys, highly reducing the quality of their life. We propose a new generation of robotic walking assistants whose mechanical and electronic components are conceived to optimize the collaboration between the robot and its users. We will apply these general ideas to investigate the interaction between older adults and a robotic walker, named FriWalk, exploiting it either as a navigational or as a rehabilitation aid. For the use of the FriWalk as a navigation assistance, the system guides the user securing high levels of safety, a perfect compliance with the social rules and non-intrusive interaction between human and machine. To this purpose, we developed several guidance systems ranging from completely passive strategies to active solutions exploiting either the rear or the front motors mounted on the robot. The common strategy at the basis of all the algorithms is that the responsibility of the locomotion belongs always to the user, both to increase the mobility of elder users and to enhance their perception of control over the robot. This way the robot intervenes only whenever it is strictly necessary not to mitigate the user safety. Moreover, the robotic walker has been endowed with a tablet and graphical user interface (GUI) which provides the user with the visual indications about the path to follow. Since the FriWalk was developed to suit the needs of users with different deficits, we conducted extensive human-robot interaction (HRI) experiments with elders, complemented with direct interviews of the participants. As concerns the use of the FriWalk as a rehabilitation aid, force sensing to estimate the torques applied by the user and change the user perceived inertia can be exploited by doctors to let the user feel the device heavier or lighter. Moreover, thanks to a new generation of sensors, the device can be exploited in a clinical context to track the performance of the users' rehabilitation exercises, in order to assist nurses and doctors during the hospitalization of older adults

Ankle-Actuated Human-Machine Interface for Walking in Virtual Reality

This thesis work presents design, implementation and experimental study of an impedance type ankle haptic interface for providing users with the immersive navigation experience in virtual reality (VR). The ankle platform enables the use of foot-tapping gestures to reproduce realistic walking experience in VR and to haptically render different types of walking terrains. The system is designed to be used by seated users allowing more comfort, causing less fatigue and motion sickness. The custom-designed ankle interface is composed of a single actuator-sensors system making it a cost-efficient solution for VR applications. The designed interface consists of a single degree of freedom actuated platform which can rotate around the ankle joint of the user. The platform is impedance controlled around the horizontal position by an electric motor and capstan transmission system. to perform walking in a virtual scene, a seated user is expected to perform walking gestures in form of ankle plantar-flexion and dorsiflexion movements causing the platform to tilt forward and backward. We present three algorithms for simulating the immersive locomotion of a VR avatar using the platform movement information. We also designed multiple impedance controllers to render haptic feedback for different virtual terrains during walking. We carried out experiments to understand how quickly users adapt to the interface, how well they can control their locomotion speed in VR, and how well they can distinguish different types of terrains presented through haptic feedback. We implemented qualitative questionnaires on the usability of the device and the task load of the experimental procedures. The experimental studies demonstrated that the interface can be easily used to navigate in VR and it is capable of rendering dynamic multi-layer complex terrains containing structures with different stiffness and brittleness properties

Master of Science

thesisThe objective of this research is to improve the ability of a human operator to drive an omnidirectional robot by using omnidirectional force-feedback. Omnidirectional vehicles offer improved mobility over conventional vehicles and can potentially benefit people requiring motorized transportation and industries where vehicles must operate in confined spaces. However, omnidirectional vehicles require more skill to control due to the additional degrees of freedom inherent in the vehicle’s design. We hypothesize that providing force-feedback to the driver through an omnidirectional joystick will allow the robot to assist the driver in navigating and avoiding collisions with obstacles in a manner that is natural to the operator. This research is the first attempt to use true omnidirectional 3-DOF (degree of freedom) force-feedback to provide navigational assistance for a human to drive an omnidirectional vehicle. While 2-DOF force-feedback has been used in a limited capacity for obstacle avoidance on omnidirectional vehicles, this is the first study to include a third rotational axis of force-feedback and use it to guide a driver along planar collision-avoiding trajectories with a natural coordination of orientation. Unique intellectual merits put forth by this research include use of a novel omnidirectional haptic device and force-feedback strategies to guide operators and experiments to quantify the ability of force-feedback to improve omnidirectional driving performance and driver experience in a real time scenario

Haptic Interface for the Simulation of Endovascular Interventions

Endovascular interventions are minimally invasive surgical procedures that are performed to diagnose and treat vascular diseases. These interventions use a combination of long and flexible instruments known as guidewire and catheter. A popular method of developing the skills required to manipulate the instruments successfully is through the use of virtual reality (VR) simulators. However, the interfaces of current VR simulators have several shortcomings due to limitations in the instrument tracking and haptic feedback systems design. A major challenge of developing physics-based training simulations of endovascular interventional procedures is to unobtrusively access the central, co-axial guidewire for tracking and haptics. This work sets out to explore the state of the art, to identify and develop novel solutions to this concentric occlusion problem, and to perform a validation of a proof of concept prototype. This multi port haptic interface prototype has been integrated with a 3-D virtual environment and features novel instrument tracking and haptic feedback actuation systems. The former involves the use of an optical sensor to detect guidewire movements through a clear catheter, whereas the latter utilises the placement of a customised electromagnetic actuator within the catheter hub. During the proof of concept validation process, both systems received positive reviews. Whilst the haptic interface prototype designed in this work has met the original objectives, there are still important aspects which need to be addressed to improve its content and face validity. With further development, the prototype has the potential to evolve and become a significant improvement over the haptic interfaces that exist today.Open Acces

磁性流体を用いたバックドライブ可能な油圧アクチュエータの開発

早大学位記番号:新7478早稲田大

Application of ultrasonic motors to MR-compatible haptic interfaces

Functional Magnetic Resonance Imagery (fMRI) is an imaging technique allowing the observation of brain activity. Haptic interfaces can be used in conjunction with fMRI to stimulate the subject while measuring brain activity. Using robotic stimulation over conventional methods offers repeatability, flexibility and the possibility of logging of different experiment variables. Such system becomes a powerful tool for neuroscience study, diagnostic and rehabilitation. The MR scanner with its high magnetic fields and radio frequency pulses is a harsh environment for a robotic system. Robots that can operate safely and do not induce disturbances in the imaging of the scanner are qualified as MR-compatible. The actuation of these robots is an important issue. Electrical power brought to the actuator represents an important source of interferences with the scanner. Since electrical motors cannot be introduced in the MR room, haptic interfaces are conventionally remotely actuated over a long transmission with the actuators placed outside of the MR room. In particular cases, such as the study of finger motion, small haptic interfaces with limited force ranges are required. Remote actuation methods impose transmission lengths and means that cannot be reduced nor scaled down thus imposing a trade-off between performances and size reduction in these applications. This work investigates an alternative actuator that can achieve high-quality force-interactions with the fingers. The Ultrasonic Motor (USM) is MR-compatible and offers good performances. But it is not well suited for force-feedback and may be hazardous for the users. To address these issues, mechanical solutions are investigated by using an electrical analogy applied to mechanical systems. A novel actuation system using the USM as a power source and a clutch to control the output torque is proposed: the Hybrid USM Clutch Actuator (HUCA). The first prototype validates the different mechanical concepts developed in this work. The second, MR-compatible, integrates a clutch based on electrorheological fluids (ER). MR-compatibility has been validated and performances evaluated. Since the HUCA has the unique property of behaving both like a force source and a velocity source, dedicated control schemes have been developed to implement impedance and admittance force control. These enable the display of stiff walls and the rendering of a wide range of impedances thanks to the overlap of their range of displayable impedances. Compared to the hydrostatic transmission actuation, the HUCA shows higher performances and user safety. Furthermore, the powering through electrical wires allows developments of multi-DOF interfaces