Pierre-Luc Richard

Type Synthesis of Parallel Mechanisms With Multiple Operation Modes

There are usually several motion patterns having the same degrees of freedom (DOF). For example, planar motion, spherical motion, and spatial translation are motion patterns with 3 DOF. An f-DOF parallel mechanism with multiple operation modes is a parallel mechanism that can generate different motion patterns with f DOF. Up to now, no method has been proposed for the type synthesis of parallel mechanisms with multiple operation modes. This paper presents a general method for the type synthesis of parallel mechanisms with multiple operation modes. Using the proposed approach, 3-DOF parallel mechanisms with both spherical and translational modes, i.e., parallel mechanism generating both a spherical motion pattern and a spatial translational motion pattern, are generated systematically. A large number of parallel mechanisms with both spherical and translational modes are obtained.

Kinematic Analysis and Prototyping of a Partially Decoupled 4-DOF 3T1R Parallel Manipulator

A four-decree-of-freedom (DOF) 3T1R parallel manipulator is presented in this paper. This manipulator generates the family of so-called Schonflies motions, SCARA motions or 3T1R motions, in which the moving platform can translate in all directions and rotate around an axis of a fixed direction. The kinematic analysis of this architecture is presented, including the study of the constraint singular configurations, kinematic singular configurations, and the determination of the workspace. A prototype (the Quadrupteron) is also presented and demonstrated. The characteristics of the proposed prototype are (a) there is no constraint singularity, (b) its input-output equations are partially decoupled, (c) its kinematic singular configurations can be expressed using, an equation in the angle of rotation of the moving platform and are thus easy to avoid at the design stage, and (d) its forward displacement analysis requires the solution of a univariate quadratic equation and can therefore be solved efficiently.

Parallel Mechanisms of the Multipteron Family: Kinematic Architectures and Benchmarking

This paper is a contribution to an invited session on the benchmarking of parallel mechanisms. The aim of the session is to compare different existing designs and prototypes of parallel mechanisms using a common set of benchmarking criteria. First, the kinematic architectures of parallel mechanisms of the multipteron family are presented. In addition to the tripteron and the quadrupteron, the pentapteron, a five-degree-of-freedom (dof) parallel mechanism is introduced. Then, the benchmarking criteria are applied to the prototypes of the tripteron (3-dof) and the quadrupteron (4-dof) prototypes. Although the tripteron and quadrupteron parallel mechanisms have been presented elsewhere, their properties, highlighted by the benchmarking analysis presented here are revealed for the first time.

A First Semimanual Device for Clinical Intramuscular Repetitive Cell Injections

Intramuscular cell transplantation in humans requires so far meticulous repetitive cell injections. Performed percutaneously with syringes operated manually, the procedure is very time consuming and requires a lot of concentration to deliver the cells exactly in the required region. This becomes impractical and inaccurate for large volumes of muscle. In order to accelerate this task, to render it more precise, and to perform injections more reproducible in large volumes of muscle, we developed a specific semimanual device for intramuscular repetitive cell injections. Our prototype delivers very small quantities of cell suspension, homogeneously throughout several needles, from a container in the device. It was designed in order to deliver the cells as best as possible only in a given subcutaneous region (in our case, skeletal muscles accessible from the surface), avoiding wasting in skin and hypodermis. The device was tested in monkeys by performing intramuscular allotransplantations of beta-galactosidase-labeled myoblasts. During transplantations, it was more ergonomic and considerably faster than manually operated syringes, facilitating the cell graft in whole limb muscles. Biopsies of the myoblast-injected muscles 1 month later showed abundant beta-galactosidase-positive myofibers with homogeneous distribution through the biopsy sections. This is the first device specifically designed for the needs of intramuscular cell transplantation in a clinical context.

LineScout Technology Opens the Way to Robotic Inspection and Maintenance of High-Voltage Power Lines

Historically, the inspection and maintenance of high-voltage power lines have been performed by linemen using various traditional means. In recent years, the use of robots appeared as a new and complementary method of performing such tasks, as several initiatives have been explored around the world. Among them is the teleoperated robotic platform called LineScout Technology, developed by Hydro-Québec, which has the capacity to clear most obstacles found on the grid. Since its 2006 introduction in the operations, it is considered by many utilities as the pioneer project in the domain. This paper’s purpose is to present the mobile platform design and its main mechatronics subsystems to support a comprehensive description of the main functions and application modules it offers. This includes sensors and a compact modular arm equipped with tools to repair cables and broken conductor strands. This system has now been used on many occasions to assess the condition of power line infrastructure and some results are presented. Finally, future developments and potential technologies roadmap are briefly discussed.

LineScout power line robot: Characterization of a UTM-30LX LIDAR system for obstacle detection

This paper presents the characterization of the Hokuyo UTM-30LX laser range finder applied to obstacle detection on power line conductors. First, an overview section defines requirements and explains why the UTM-30LX was selected for this application. Next, since there is no published characterization of this particular sensors performance, a comprehensive set of experiments is described, both general tests and ones specific to the novel problem of scanning a power line conductor to detect where obstructions are present. It is then explained how the LIDAR can be mounted on the LineScout power line robot and what algorithm is used to detect obstacles ahead. Basic results obtained on a full-scale power line mock-up clearly demonstrate the potential of the approach.

Discrete-Time State Feedback With Velocity Estimation Using a Dual Observer: Application to an Underwater Direct-Drive Grinding Robot

Hydro-Quebecs Research Institute has designed a robot to perform grinding tasks on underwater structures. This unique system is equipped with direct-drive linear motors, which have many useful dynamic characteristics. Since they lack intrinsic stiffness, however, their robustness to external disturbances must be achieved through the controller. Their lack of stiffness is a major disadvantage, because grinding generates very strong disturbance forces. Moreover, controller performance in such a system is limited by velocity feedback, which is usually derived from position encoder data. Though the state observer is recognized as an effective way to estimate velocity from position feedback without delay, it is not robust when applied to a system sensitive to external disturbances. The dual observer, which combines a state observer and a perturbation observer, aims to solve this problem. The simultaneous estimation of the state and disturbance not only improves state observer robustness, but also helps to compensate for disturbances in the controller. This paper presents the design of a discrete- time state-feedback controller with velocity estimation through a discrete- time dual observer. The design is validated by extensive comparative testing for a task that is as intensive as underwater grinding.

Introduction of a LIDAR-based obstacle detection system on the LineScout power line robot

This paper is a sequel of an earlier paper that featured a thorough characterization of the Hokuyo UTM-30LX laser range finder, which showed promise for a specific application: allowing a power line robot to detect obstacles in its path. After a quick summary of the earlier conclusions, this paper pushes the validation farther by assessing for the first time this popular LIDARs performance when subjected to the particularly challenging, outdoor, power line environmental conditions: large temperature range, changes in lighting, strong magnetic fields, and oscillating or vibrating targets. Use of return signal intensity, predictably affected by the angle of incidence on the target and by target surface finish, is also investigated as a means to detect variations due to an obstacle. Scanning results with LineScout traveling at maximum speed on a full-scale power line span are then analyzed to validate the proposed detection thresholds.

Multiobjective optimization of an observer-based controller: theory and experiments on an underwater grinding robot

Hydro-Québec operates hundreds of dikes and dams built many decades ago, and is committed to the long-term sustainability of these facilities. The researchers and engineers at its research institute have designed and manufactured a submersible grinding robot prototype capable of performing the important task of grinding underwater metallic structures. This robot, with direct drive linear motors, has an excellent dynamic performance, but lacks intrinsic stiffness. The design of a control system for such a system is a major challenge for control engineers, as the algorithm must achieve sufficient dynamic stiffness to withstand the significant external perturbations generated by the grinding process and the underwater environment, while at the same time minimizing the sensitivity of the control effort to measurement noise. A discrete-time observer-based control structure has already been proposed in a previous work for this purpose, but the empirical design procedure for this structure did not consider the two contradictory objectives. Using the same controller structure, we propose a new design methodology in this brief, based on a multiobjective genetic algorithm, for these mechatronic systems, which are highly prone to the effects of disturbances. The results obtained through optimization are compared with those obtained using the empirical method. The effectiveness of the proposed design is demonstrated through underwater grinding experiments using the robot test bench we have developed.

Position tracking control of a direct-drive submersible grinding robot: A comparative study

This paper presents a comparative study of a sliding-mode controller (SMC) and a cascaded proportional/proportional integral (P/PI) controller with zero-phase error tracking controller (ZPETC) and disturbance observer (DOB). The tests are performed on a new underwater grinding robot. The comparison is based on trajectory tracking performance and robustness to external disturbances, such as those induced by the underwater environment and the grinding process. Experimental results show that for the same design criteria the P/PI controller produces better performance in terms of trajectory tracking error and disturbance rejection. The DOB was shown to be a simple and effective way to further reduce the positioning error.