A virtual holonomic constraint (VHC) for an Euler-Lagrange Control System is a smooth relation between the configuration variables that can be made invariant through application of suitable feedback. In this thesis we investigate the role played by VHCs in the synchronization of Euler-Lagrange systems. We focus on two problems. For $N$ underactuated cart-pendulums, we design a smooth feedback that fully synchronizes the cart-pendulums while simultaneously stabilizing a periodic orbit corresponding to a desired oscillation for the pendulums. A by-product of our results is the ability to simultaneously synchronize the pendulums and stabilize the unstable upright equilibrium. The second synchronization problem investigated in this thesis is bilateral teleoperation, whereby a master robot is operated by a human while a slave robot synchronizes to the master. For two identical planar manipulators, we develop a methodology to achieve teleoperation in the presence of a hard surface, with simultaneous force control.

This thesis examines the haptic rendering of rigid point contacts in virtual simulations. The haptic renderers generate force feedback so that the operator can interact with the virtual scenes in a realistic way. They must be able to recreate the physical phenomena experienced in the real world without displaying any haptic artifacts. The existing renderers are decomposed into a projection function and a regulation scheme. It is shown that the pop-through artifact, whereby the virtual tool instantaneously jumps between two distant surface points, is caused whenever the operator encounters a singularity within the renderer's projection function. This was well known for the minimum distance based renderers, but it is shown here that such singularities arise with the constraint based renderers as well. A new projection function is designed to minimize the existence of singularities within the model. When paired with an appropriate regulation scheme, this forms the proposed mapping renderer. The new projection is calculated by mapping the model onto a canonical shape where the haptic problem is trivial, e.g. a circle in the case of a 2D model of genus zero, which avoids pop-through on smooth models. The haptic problem is then recast as a virtual constraint problem, where the traditional regulation schemes, designed originally for planar surfaces, are shown to introduce a velocity dependent error on curved surfaces that can distort the model's rendering and to couple the regulation towards and dynamics along the constraint. Set stabilization control, based on feedback linearizing the haptic device with respect to a virtual output consisting of coordinates transversal and tangential to the model surface, is proposed as an alternative. It is shown to be able to decouple the system into transversal and tangential subsystems that can then be made asymptotically stable and assigned arbitrary dynamics, respectively.

A haptic system is a robotic computer interface which aims to provide tactile feedback for human operators when they manipulate virtual environments (VEs) or remote environments (REs). The tactile feedback is emulated by applying forces, vibrations, or motions to the human users through a haptic device/interface, e.g. a robot arm. Transparency and stability are two important criteria for designing a haptic system. Transparency is related to the realism of user's touch sensation and stability guarantees the safety of the user while interacting with VEs/REs. Because of the nature of the human tactile sensory system, a transparent haptic system demands an update rate greater than 500 Hz, i.e. most commercial haptic devices work at 1 KHz. On the other hand, many haptic applications are multirate systems. The multirate property of a haptic system is due to either the slow update rate of the VE or the impairments of computer networks such as limited transmission bandwidth or packet loss. Wave transformation is wildly used in teleoperation to cope with both constant and varying time delays. This work aims to use wave transformation to tackle the challenges imposed by multirate property of a haptic system. First, passive multirate wave variables control (PMWVC) is introduced. PMWVC guarantees the passivity of the communication channels through which the fast haptic device is connected to the slow VE/RE. It is shown that to maintain the passivity of the system, aliasing should be avoided in the communication channels, i.e. by using anti-aliasing filters. Next, PMWVC strategy is applied to two different applications: i) multiuser cooperative haptics and ii) haptic interaction with an unknown VE. In the first application, two users at two different locations manipulate a common virtual object simulated on a central server. The users are connected to the central server through a LAN network. The second application is a single user application in which PMWVC is used to connect the haptic device to an unknown slowly updated VE. Since in this application the VE is unknown, the computational delay of the VE significantly affects the stability of the overall system. To tackle this problem, a nonlinear algorithm based on passivity analysis is proposed. In both examples, numerical and experimental results validating the analytical results are provided. The results show that by using PMWVC, it is possible to significantly improve the performance of a multirate haptic system in terms of transparency and stability. The second half of this work is devoted to improving the performance of PMWVC in all frequency ranges. In order to study the performance of PMWVC, lifting is used to convert the multirate haptic system to a unirate system. By using this technique, it is shown that velocity estimation plays a critical role in a haptic application with PMWVC, especially in high frequencies. Considering this fact, a method for designing a passive velocity filter in wave domain is proposed. Finally, a filter bank structure is introduced which enables utilizing a local model in conjunction with PMWVC. In this structure, the outgoing signal sent to the VE is split into two frequency ranges. Low frequency content of the signal is fed to the original VE and high frequency content of the signal is sent to the local model. By using lifting the performance of the proposed structure is studied. The results show that the proposed method improves the transparency of the system in all frequency ranges and unlike utilizing a local model in power domain, it does not impose any restriction on the stability of the system. / Graduate / 0548 / 0544 / 0771 / nyasrebi@uvic.ca

This thesis examines the haptic rendering of rigid point contacts in virtual simulations. The haptic renderers generate force feedback so that the operator can interact with the virtual scenes in a realistic way. They must be able to recreate the physical phenomena experienced in the real world without displaying any haptic artifacts. The existing renderers are decomposed into a projection function and a regulation scheme. It is shown that the pop-through artifact, whereby the virtual tool instantaneously jumps between two distant surface points, is caused whenever the operator encounters a singularity within the renderer's projection function. This was well known for the minimum distance based renderers, but it is shown here that such singularities arise with the constraint based renderers as well. A new projection function is designed to minimize the existence of singularities within the model. When paired with an appropriate regulation scheme, this forms the proposed mapping renderer. The new projection is calculated by mapping the model onto a canonical shape where the haptic problem is trivial, e.g. a circle in the case of a 2D model of genus zero, which avoids pop-through on smooth models. The haptic problem is then recast as a virtual constraint problem, where the traditional regulation schemes, designed originally for planar surfaces, are shown to introduce a velocity dependent error on curved surfaces that can distort the model's rendering and to couple the regulation towards and dynamics along the constraint. Set stabilization control, based on feedback linearizing the haptic device with respect to a virtual output consisting of coordinates transversal and tangential to the model surface, is proposed as an alternative. It is shown to be able to decouple the system into transversal and tangential subsystems that can then be made asymptotically stable and assigned arbitrary dynamics, respectively.

The temporal bone is an anatomically complex region within the skull. Current training for temporal bone surgery includes cadaveric, physical and virtual haptic simulations and apprenticeships. Cadavers are limited by low supply. Haptic devices are limited by their force and stiffness ratings and thus cannot adequately simulate rigid materials. Physical simulations excel at simulating stiff materials but do a poor job of soft tissue. The research objective was to develop a mixed reality (MR) temporal bone surgical haptic simulation. This novel concept would utilize physical models to simulate bone and haptic forces to simulate soft tissue. A surgical drill was attached to a Quanser® High Definition Haptic DeviceTM (HD2) via a clamp. An algorithm was implemented to simulate a force at the drill tip and to negate the weight of the clamp. This modified haptic system was interfaced to a temporal bone haptic simulation. Haptic chatter unique to the modified haptic system was observed and low-pass filters were used to mitigate this issue. Due to the poor positional accuracy of the HD2, MR simulation was not achieved. However, VR haptic simulation was achieved. Six expert surgeons were recruited to investigate the following questions: "What is the impact of different haptic hardware on surgical realism?" and "Would end users prefer a surgical drill over a standard haptic manipulandum?" Three cases were compared: a Phantom Omni®, a standard HD2 and a modified HD2 with attached drill. Expert surgeons rated the standard HD2 and Phantom Omni equivalently whilst preferring the modified HD2 with attached drill. Though the modified HD2 scored higher in all categories only “Acoustics” and “Overall Appreciation” displayed statistical significance. This implies that drill acoustics is critical for realism. / February 2016

abstract: Humans constantly rely on a complex interaction of a variety of sensory modalities in order to complete even the simplest of daily tasks. For reaching and grasping to interact with objects, the visual, tactile, and proprioceptive senses provide the majority of the information used. While vision is often relied on for many tasks, most people are able to accomplish common daily rituals without constant visual attention, instead relying mainly on tactile and proprioceptive cues. However, amputees using prosthetic arms do not have access to these cues, making tasks impossible without vision. Even tasks with vision can be incredibly difficult as prosthesis users are unable to modify grip force using touch, and thus tend to grip objects excessively hard to make sure they don’t slip. Methods such as vibratory sensory substitution have shown promise for providing prosthesis users with a sense of contact and have proved helpful in completing motor tasks. In this thesis, two experiments were conducted to determine whether vibratory cues could be useful in discriminating between sizes. In the first experiment, subjects were asked to grasp a series of hidden virtual blocks of varying sizes with vibrations on the fingertips as indication of contact and compare the size of consecutive boxes. Vibratory haptic feedback significantly increased the accuracy of size discrimination over objects with only visual indication of contact, though accuracy was not as great as for typical grasping tasks with physical blocks. In the second, subjects were asked to adjust their virtual finger position around a series of virtual boxes with vibratory feedback on the fingertips using either finger movement or EMG. It was found that EMG control allowed for significantly less accuracy in size discrimination, implying that, while proprioceptive feedback alone is not enough to determine size, direct kinesthetic information about finger position is still needed. / Dissertation/Thesis / Masters Thesis Bioengineering 2016

Artistic painting involves mastery of haptic interaction with tools. Each tool brings unique physical affordances which determines an aesthetic expression of the finished work. For instance, a pen offers an ability to make a precise stroke in a realism painting, whereas a thick brush or a sponge works perfectly with dynamic arm movement in the abstract art such as action painting. Yet the selection of a tool is just a beginning. It requires repetitive training to understand the full capability of the tool affordance and to master the painting of preferred aesthetic strokes. Such physical act of an artistic expression cannot be captured by the computational tools today. Due to the increasing market adoption of augmented reality and virtual reality, and the decades of studies in haptics, we see an opportunity for advancing 3D painting experiences in non-conventional approach. In this research, we focus on force haptic interaction for 3D painting art in a room-scale virtual reality. We explore virtual tangibility and tool affordance of its own medium. In addition to investigating the fidelity of a physical interactivity, we seek ways to extend the painting capabilities by computationally customized force feedback and metaphor design. This system consists of a wearable force feedback device that sits on user’s hand, a software for motor control and real-time 3D stroke generation, and their integration to VR platform. We work closely with an artist to refine the 3D painting application and to evaluate the system’s usability.

Haptic, or force, interaction in virtual environments can support the development of physical manipulation skills if users feel realistic forces in response to their motion in the virtual environment. The realism of the forces felt by users depends on: (i) how accurately the virtual environment simulates a real life situation such as surgery; and (ii) how faithfully the haptic controller renders the simulated interactions to users. Accurate simulations of real life situations such as surgery run at variable frequencies of the order of 20-100 Hz. However, the haptic controller needs updated stiffness and direction of contact at 1000 Hz to faithfully convey the shape and hardness of the virtual objects to the user. This thesis proposes to bridge the gap between the required fast haptic control rate and the slower virtual environment updates through a passive local model of interaction. This model comprises an approximation of the shape and stiffness of the virtual world in the area near the point of interaction. It also monitors its exchange of energy with the user to ensure its own passivity and thus, the stability of the haptic system. Lastly, the local model eliminates the spurious discontinuities that arise in contact direction at model updates by interpolating the contact normal before rendering it to the user. / Graduate

The subject of diploma project is constructional solution of haptics interface construction for virtual reality output device. Construction is oriented only for virtual contact with objects. Force feedback on the user and deformation of objects are not used. Used programs: Autodesk INVENTOR 10, ANSYS WORKBENCH.

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