Flavio Firmani

An Explicit Method for Determining the Force-Moment Capabilities of Redundantly Actuated Planar Parallel Manipulators

A new explicit methodology for the determination of the force-moment capabilities of nonredundantly and redundantly actuated planar parallel manipulators (PPMs) is presented. This methodology is based on properly adjusting the actuator outputs to their maximum capabilities. As a result, the wrench to be applied or sustained is maximized. For a nonredundantly actuated PPM, one actuator can be maximized, while for a redundantly actuated PPM, one actuator, beyond the one of the nonredundant case, may be maximized for every degree of redundancy added to the mechanism. This methodology is compared to a previous work that required an optimization algorithm. The new method yields more accurate and reliable results and is considerably more efficient. Four studies of force-moment capabilities are considered: maximum force with prescribed moment, maximum applicable force, maximum moment with a prescribed force, and maximum applicable moment. The methodology is used to generate the force-moment capabilities of an existing PPM throughout its workspace.

Wrench capabilities of planar parallel manipulators. part i: Wrench polytopes and performance indices

This paper is organized in two parts. In Part I, the wrench polytope concept is presented and wrench performance indices are introduced for planar parallel manipulators (PPMs). In Part II, the concept of wrench capabilities is extended to redundant manipulators and the wrench workspace of different PPMs is analyzed. The end-effector of a PPM is subject to the interaction of forces and moments. Wrench capabilities represent the maximum forces and moments that can be applied or sustained by the manipulator. The wrench capabilities of PPMs are determined by a linear mapping of the actuator output capabilities from the joint space to the task space. The analysis is based upon properly adjusting the actuator outputs to their extreme capabilities. The linear mapping results in a wrench polytope. It is shown that for non-redundant PPMs, one actuator output capability constrains the maximum wrench that can be applied (or sustained) with a plane in the wrench space yielding a facet of the polytope. Herein, the determination of wrench performance indices is presented without the expensive task of generating polytopes. Six study cases are presented and performance indices are derived for each study case.

Wrench capabilities of planar parallel manipulators. part ii: Redundancy and wrench workspace analysis

This part of the paper investigates the wrench capabilities of redundantly actuated planar parallel manipulators (PPMs). The wrench capabilities of PPMs are determined by mapping a hypercube from the torque space into a polytope in the wrench space. For redundant PPMs, one actuator output capability constrains the wrench space with a smaller polytope that is contained inside the overall polytope. Performance indices are derived from six study cases. These indices are employed to analyze the wrench workspace for constant orientation of the mobile platform of the non-redundant 3-RRR PPM, and actuation redundant 4-RRR and 3-RRR PPMs, where the underline indicates the actuated joints. A comparison of the results shows that both of the redundantly-actuated PPMs give better wrench capabilities than the non-redundant PPM. However, it is shown that scaled for the operational cost (wrench capabilities divided by total actuation output) the non-redundant 3-RRR PPM provides the highest maximum reachable force, the 3-RRR PPM produces the highest isotropic force, and the 4-RRR yields the highest reachable moment.

Dynamic modelling and simulation of a multi-regime hybrid vehicle powertrain architecture

In this work, the dynamic model of a multi-regime hybrid vehicle powertrain architecture is presented. The study focuses on the formulae governing the operation of the planetary gear systems in the powertrain and on the performance of a more complex heavy-duty vehicle with varying loading conditions. The model is compared with models of the Toyota Hybrid System, a generic full-parallel design, and a conventional powertrain, all implemented for a commercial delivery vehicle in the ADVISOR simulation software. Computer simulations in ADVISOR compare the performance of the various designs, using fuel consumption as the performance metric, for four different drive cycles common for this vehicular application. The results demonstrate that the multi regime architecture provides significantly improved performance to that of the conventional and THS design and comparable performance to that of the full parallel hybrid design. The study confirms that the multi-regime architecture presents unique advantages for wide-ranging road loads and vehicle payloads and that multi-regime designs likely represent the future of hybrid vehicle technology.

Comprehensive underwater vehicle-manipulator system teleoperation

In this work, a novel comprehensive scheme for the coordinated control of remotely operated vehicle-manipulator systems (ROVMs) is proposed. In the proposed scheme, instead of commanding the motion of the vehicle and the manipulator separately, a human pilot commands only the manipulators end-effector motion using a parallel- architectured six-degree-of-freedom (6-DOF) joystick. The generated reference motion is then converted into a set of desired ROV and manipulator joint motion by means of using a redundancy resolution scheme that provides the means to utilize redundant degrees of freedom to accomplish secondary objectives. The redundancy resolver uses the Gradient Projection Method combined with a Mamdani-based fuzzy determination of the hierarchy of the secondary objectives. The controller relies on a unified dynamic model of the system. The quasi-Lagrange method is used to derive the equations of motion in terms of the ROV body-fixed frame. For the control problem, a sliding-mode based controller is used that contains an adaptive term for the estimation of the upper bound on the lumped uncertainty vector. The hardware-in-the-loop simulation studies illustrate that detailed subsea tasks can be completed with a small, low-cost ROVM system using the proposed ROVM operation scheme.

An Analysis of the Force-Moment Capabilities of Branch-Redundant Planar-Parallel Manipulators

The force-moment capabilities of branch-redundant planar-parallel manipulators (PPMs) are investigated. A previously developed explicit methodology for generating the force-moment capabilities of redundant PPMs is used on three different PPM architectures. The results for the 4-R RR, 4-R PR, 4-P RR layouts (where the underline denotes the actuated joint in each branch) are presented and discussed. For the revolute-actuated layouts, it was shown that the force-moment capabilities for the 4-R RR were in general better than those of the 4-R PR for the chosen manipulator parameters. The presented analysis is an effective tool for designing PPMs to determine the largest forces and moments that can be applied at any point within the workspace.Copyright

Wrench Capabilities of Planar Parallel Manipulators and their Effects Under Redundancy

where J is referred to as the Jacobian matrix. In addition, an extended problem can be formulated as the analysis of the maximum twist or wrench that the end-effector can perform in the twist or wrench spaces, respectively. The knowledge of maximum twist and wrench capabilities is an important tool for achieving the optimum design of manipulators. For instance, by being able to graphically visualize the twist and wrench capabilities, comparisons between different design parameters, such as the actuator torque capabilities and the dimensions of the links, can be explored. Also, the performance of an existing manipulator can be improved by identifying the optimal capabilities based on the configuration of the branches and the pose of the end-effector. This work focuses on the wrench capabilities of planar parallel manipulators (PPMs), the geometric interpretation of their wrench polytopes, the derivation of wrench performance indices, and how the inclusion of redundancy affects the performance of parallel manipulators (PMs). The wrench capability analysis of a manipulator depends on its design, posture, and actuator torque capabilities.

A framework for the analysis and synthesis of 3d dynamic human gait

A comprehensive framework for the analysis and synthesis of 3D human gait is presented. The framework consists of a realistic morphological representation of the human body involving 40 degrees of freedom and 17 body segments. Through the analysis of human gait, the joint reaction forces/moments can be estimated and parameters associated with postural stability can be quantified. The synthesis of 3D human gait is a complicated problem due to the synchronisation of a large number of joint variables. Herein, the framework is employed to reconstruct a dynamically balanced gait cycle and develop sets of reference trajectories that can be used for either the assessment of human mobility or the control of mechanical ambulatory systems. The gait cycle is divided into eight postural configurations based on particular gait events. Gait kinematic data is used to provide natural human movements. The balance stability analysis is performed with various ground reference points. The proposed reconstruction of the gait cycle requires two optimisation steps that minimise the error distance between evaluated and desired gait and balance constraints. The first step (quasi-static motion) is used to approximate the postural configurations to a region close to the second optimisation step target while preserving the natural movements of human gait. The second step (dynamic motion) considers a normal speed gait cycle and is solved using the spacetime constraint method and a global optimisation algorithm. An experimental validation of the generated reference trajectories is carried out by comparing the paths followed by 19 optical markers of a motion tracking system with the paths of the corresponding node points on the model.

Gait Speed and Variability for Usual Pace and Pedestrian Crossing Conditions in Older Adults Using the GAITRite Walkway

Objectives: To determine gait characteristics of community-dwelling older adults at different speeds and during a crosswalk simulation. Methods: Twenty-two older adults completed walking trials at self-selected slow, usual, and fast paces, and at a crosswalk simulation, using the GAITRite walkway. These objective measures were complemented by self-report health and mobility questionnaires. Results: Gait speeds at self-selected slow, usual, and fast paces were 98.7 (18.1) cm/s, 140.9 (20.4) cm/s, and 174.0 (20.6) cm/s, respectively, and at simulated crosswalk conditions was 144.2 (22.3) cm/s. For usual pace, right step length variability was 2.0 (1.4) cm and step time variability was 13.6 (7.2) ms, compared with 2.4 (1.3) cm and 17.3 (9.7) ms, respectively, for crosswalk conditions. Discussion: Our sample of healthy older adults walked at a speed exceeding standards for crossing urban streets; however, in response to a crosswalk signal, participants adopted a significantly faster and more variable gait.