Simon Perreault

Median Filtering in Constant Time

The median filter is one of the basic building blocks in many image processing situations. However, its use has long been hampered by its algorithmic complexity O(tau) of in the kernel radius. With the trend toward larger images and proportionally larger filter kernels, the need for a more efficient median filtering algorithm becomes pressing. In this correspondence, a new, simple, yet much faster, algorithm exhibiting O(1) runtime complexity is described and analyzed. It is compared and benchmarked against previous algorithms. Extensions to higher dimensional or higher precision data and an approximation to a circular kernel are presented, as well.

Cable-Driven Parallel Mechanisms: Application to a Locomotion Interface

Over the past decade, cable-driven parallel mechanisms have been used for several purposes. In this paper, a novel application is proposed, namely, using two 6DOF cable-driven parallel mechanisms sharing a common workspace to obtain the mechanical base for the design of a locomotion interface. The methodology used to develop the architecture of the mechanisms is presented, and the two main criteria used to optimize the geometry are described. These criteria are based on the wrench-closure workspace and a detection of the mechanical interferences between all the entities of the locomotion interface (cables and moving bodies). Then, the final design is described and its performances are given. Finally, in order to validate the relevance of the mechanism for the locomotion interfaces design, tensile forces in the cables are computed to observe the maximal values reached during a typical human gait trajectory.

Determination and Management of Cable Interferences Between Two 6-DOF Foot Platforms in a Cable-Driven Locomotion Interface

The intrinsic interaction of a robotic system that includes two 6-degree-of-freedom cable-driven platforms sharing a common workspace might result in cable interferences for random trajectories. This paper presents and analyzes computational methods for geometrically determining and managing these interferences for any trajectory constrained with variable loads. The algorithms considered determine which cable can be released from an active actuation state while allowing control in a minimal tension state, thereby ensuring that both platforms stay in a controllable workspace. The process of managing cable interferences constitutes a challenge as one must take into account the inherent limitations of the workspace, which not only include the possibility of interference itself, but also the geometry of the cable-driven locomotion interface (CDLI), its dynamics, the nonideal behavior of real cables, and the requirement that both platforms must be completely constrained at any time. As releasing a cable from an active actuation state might generate tension discontinuities in the other cables, this paper also proposes collision prediction schemes that are only applied to redundant actuators in order to reduce or completely eliminate such discontinuities. Finally, a simulation of a CDLI embedded as a peripheral in a virtual environment, in which the load applied on each platform comes from the wrench measured under the foot for a natural gait walking, is thoroughly analyzed.

Geometric Determination of the Interference-Free Constant-Orientation Workspace of Parallel Cable-Driven Mechanisms

The increasing use of parallel cable-driven mechanisms calls for a better understanding of their behavior and highly efficient algorithms to attenuate their drawbacks at the design stage. One of these drawbacks is the high probability of mechanical interferences between the moving parts of the mechanism. In this paper, the phenomenon is described under the assumption that a cable is a line segment in space. When a mechanical contact occurs between two cables or between a cable and an edge of the end effector, these entities necessarily lie in the same plane, and then the three-dimensional problem becomes two-dimensional. This fact is used to simplify the equations, and leads to exhaustive descriptions of the associated interference loci in the constant-orientation workspace of a cable-driven mechanism. These results provide a fast method to graphically represent all interference regions in the manipulator workspace, given its geometry and the orientation of its end effector.

A Cable-driven Parallel Mechanism for Capturing Object Appearance from Multiple Viewpoints

This paper presents the full proof of concept of a system for capturing the light field of an object. It is based on a single high resolution camera that is moved all around the object on a cable-driven end-effector. The main advantages of this system are its scalability and low interference with scene lighting. The camera is accurately positioned along hemispheric trajectories by observing target features. From the set of gathered images, the visual hull is extracted and can be used as an approximate geometry for mapping a surface light field. The paper describes the acquisition system as well as the modeling process. The ability of the system to produce models is validated with four different objects whose sizes range from 20 cm to 3 m.

A Dual-Arm 7-Degrees-of-Freedom Haptics-Enabled Teleoperation Test Bed for Minimally Invasive Surgery

This paper describes a dual-arm teleoperation (master-slave) system which has been developed to explore the effect of haptics in robotics-assisted minimally invasive surgery (RAMIS). This setup is capable of measuring forces in 7 degrees of freedom (DOF) and fully reflecting them to the operator through two 7-DOF haptic interfaces. An application of the test bed is in enabling the evaluation of the effect of replacing haptic feedback by other sensory cues such as visual representation of haptic information (sensory substitution). This paper discusses the design rationale, kinematic analysis and dynamic modeling of the robot manipulators, and the control system developed for the setup. Using the accurate model developed in this paper, a highly transparent haptics-enabled system can be achieved and used in robot-assisted telesurgery. Validation results obtained through experiments are presented and demonstrate the correctness and effectiveness of the developed models. The application of the setup for two RAMIS surgical tasks, a suture manipulation task and a tumor localization task, is described with different haptics modalities available through the developed haptics-enabled system for each application.

A 7-DOF haptics-enabled teleoperated robotic system: Kinematic modeling and experimental verification

The purpose of this paper is to demonstrate the development of a novel 7-degree-of-freedom teleoperated robotic system that provides force reflection to the surgeons hands while performing minimally invasive surgery and therapy (MIST). An endoscopic tool has been sensorized and modified for use as the end effector of this haptics-enabled system. In this paper, mathematical models required for controlling the main components of the system have been determined and experimentally validated. Several experiments have been performed with this MIST robotic system in order to compare its force exertion capabilities with those of the da Vinci system from Intuitive Surgical Inc. Force reflection from the slave to the master in the new system is also demonstrated experimentally.

Cartesian Control of a Cable-Driven Haptic Mechanism

Haptic devices operated through a communication network require a trade-off between the stability of the interaction and the quality of the haptic display. A haptic device must be designed to provide the best haptic display in order to reproduce the tactile sensation of virtual objects, rigid or soft, while ensuring a stable operation to guarantee user safety. The challenges are greater when considering a locomotion interface where a walker can produce large wrenches. A Cable-Driven Locomotion Interface, used as a peripheral in a virtual environment, is designed to address some of the aforementioned issues, since the use of cables as a mechanical transmission is known to provide many advantages such as low inertia, which is helpful in attaining high speeds and high accelerations, and the potential lengths of the cables can allow for large workspaces. Using this mechanism, a walker could navigate in a virtual environment with the aid of two haptic platforms (one for each foot) which can be regarded as two independent parallel robots constrained to six degrees of freedom and sharing a common workspace.

Towards Parallel Cable-Driven Pantographs

We propose a new class of pantographs, i.e., of mechanisms that allow the reproduction of the displacements of an input link, the master, with an output link, the slave. The application we envision for these devices is the telemanipulation of objects from small distances, at low cost, where magnetic fields or other design constraints prohibit the use of electromechanical systems. Despite the long history of pantographs, which were invented in the 17th century, the class of pantographs proposed here is new, as it relies on parallel cable-driven mechanisms to transmit the motion. This allows the reproduction of rigid-body displacements, while previous pantographs were limited to point displacements. This important characteristic and others are described in the paper. One important challenge in the design of the proposed systems is that the cables must remain taut at all time. We address this issue by introducing nonlinear springs that passively maintain a minimum tension in the cables, while approximating static balancing of the mechanism over its workspace. Approximating static balancing allows the forces applied at the slave to reflect more accurately at the master, and vice versa. As a preliminary validation, a two-degree-of-freedom parallel cable-driven pantograph is designed. A prototype of this apparatus that does not include approximate static balancing is built, which demonstrates the working principle of these mechanisms.Copyright