Experimental Validation of the Kinematics of a 3PRS Compliant Mechanism for Micromilling

The present work deals with the development of a hybrid manipulator of 5 degrees of freedom for milling moulds for microlenses. The manipulator is based on a XY stage under a 3PRS compliant parallel mechanism. The mechanism takes advantage of the compliant joints to achieve higher repetitiveness, smoother motion and a higher bandwidth, due to the high precision demanded from the process, under 0.1 micrometers. This work is focused on the kinematics of the compliant stage of the hybrid manipulator. First, an analysis of the workspace required for the milling of a single mould has been performed, calculating the displacements required in X, Y, Z axis as well as two relative rotations between the tool and the workpiece from a programmed toolpath. Then, the 3PRS compliant parallel mechanism has been designed using FEM with the objective of being stiff enough to support the cutting forces from the micromilling, but flexible enough in the revolution and spherical compliant joints to provide the displacements needed. Finally, a prototype of the 3PRS compliant mechanism has been built, implementing a motion controller to perform translations in Z direction and two rotations. The resulting displacements in the end effector and the actuated joints have been measured and compared with the FEM calculations and with the rigid body kinematics of the 3PRS.

Design, Kinematics and Prototype of a Flexible Robot Arm With Planar Springs

Flexible robot arms have been developed for various medical and industrial applications because of their compliant structures enabling safe environmental interactions. This paper introduces a novel flexible robot arm comprising a number of elastically deformable planar spring elements arranged in series. The effects of flexure design variations on their layer compliance properties are investigated. Numerical studies of the different layer configurations are presented and finite Element Analysis (FEA) simulation is conducted. Based on the suspended platform’s motion of each planar spring, this paper then provides a new method for kinematic modeling of the proposed robot arm. The approach is based on the concept of simultaneous rotation and the use of Rodrigues’ rotation formula and is applicable to a wide class of continuum-style robot arms. At last, the flexible robot arms respectively integrated with two different types of compliance layers are prototyped. Preliminary test results are reported.

Mechanism Design and Simulation of the ULTRA Spine: A Tensegrity Robot

The Underactuated Lightweight Tensegrity Robotic Assistive Spine (ULTRA Spine) project is an ongoing effort to create a compliant, cable-driven, 3-degree-of-freedom, underactuated tensegrity core for quadruped robots. This work presents simulations and preliminary mechanism designs of that robot. Design goals and the iterative design process for an ULTRA Spine prototype are discussed. Inverse kinematics simulations are used to develop engineering characteristics for the robot, and forward kinematics simulations are used to verify these parameters. Then, multiple novel mechanism designs are presented that address challenges for this structure, in the context of design for prototyping and assembly. These include the spine robot’s multiple-gear-ratio actuators, spine link structure, spine link assembly locks, and the multiple-spring cable compliance system.

Analyzing Motion Properties of Proteins Affected by Localized Structures From a Robot Kinematics Perspective

On the basis of robot kinematics, we have thus far developed a method for predicting the motion of proteins from their 3D structural data given in the Protein Data Bank (PDB data). In this method, proteins are modeled as serial manipulators constrained by springs and the structural compliance properties of the models are evaluated. We focus on localized instead of whole structures of proteins. Employing the same model used in our method of motion prediction, the motion properties of the localized structures and the relation between the motion properties of localized and whole structures are analyzed. First, we present a method for graphically expressing the deformation of objects with a complex shape, such as proteins, by approximating the shape as a rectangular prism with a mesh on its surface. We then formulate a method for comparing the motion properties of localized structures cleaved from the whole structure and those remaining in it by expressing the motion of the latter using the decomposed motion modes of the former according to the structural compliance. Finally, we show a method for evaluating the effect of a localized structure on the motion properties of proteins by applying forces to localized structures. In the formulations, we demonstrate applications as illustrative examples using the PDB data of a real protein.

Development of a Methodology for Pseudo-Rigid-Body Models of Compliant Beams With Inserts, and Experimental Validation

Compliant mechanisms have shown a great deal of potential, in just a few decades of its development, in providing innovative solutions to design problems. However, their use has been limited due to challenges associated with the materials. With ever increasing focus on the applications of compliant mechanisms, it is necessary to find alternatives to the existing material usage and methods of prototyping. This paper presents a methodology for the design of compliant segments and compliant mechanisms with improved creep resistance and fatigue life properties using the current state-of-the-art materials. The methodology proposes using a stronger material at the core of a softer casing. The paper provides an equivalent pseudo-rigid-body model and a closed-form elliptic integral formulation for a fixed-free compliant segment with an insert. The equivalent pseudo-rigid-body model is verified experimentally for the prediction of beam end point displacements. The paper also presents experimental results that show improvements obtained in the creep recovery properties as expected using the proposed design philosophy.

Design of a Constant-Force Flexure Micropositioning Stage With Long Stroke

This paper presents the design and analysis a flexure-guided compliant micropositioning stage with constant force and large stroke. The constant force output is achieved by combining a bistable flexure mechanism with a positive-stiffness flexure mechanism. In consideration of the constraint of conventional tilted beam-based bistable mechanism, a new type of bistable structure based on tilted-angle compound parallelogram flexure is proposed to achieve a larger range of constant force output while maintaining a compact physical size. To facilitate the parametric design of the flexure mechanism, analytical models are derived to quantify the stage performance. The models are verified by carrying out nonlinear finite-element analysis. Results demonstrate the effectiveness of the proposed ideas for a long-stroke, constant-force compliant mechanism dedicated to precision micropositioning applications.

Tool-Tissue Force Estimation for a 3-DOF Robotic Surgical Tool

Robotic minimally invasive surgery has achieved success in various procedures; however, the lack of haptic feedback is considered by some to be a limiting factor. The typical method to acquire tool-tissue reaction forces is attaching force sensors on surgical tools, but this complicates sterilization and makes the tool bulky. This paper explores the feasibility of using motor current to estimate tool-tissue forces, and demonstrates acceptable results in terms of time delay and accuracy. This sensorless force estimation method sheds new light on the possibility of equipping existing robotic surgical systems with haptic interfaces that require no sensors and are compatible with existing sterilization methods.

An Innovative Navigation Strategy for Autonomous Underwater Vehicles: An Unscented Kalman Filter Based Approach

Developing reliable navigation strategies is mandatory in the field of Underwater Robotics and in particular for Autonomous Underwater Vehicles (AUVs) to ensure the correct achievement of a mission. Underwater navigation is still nowadays critical, e.g. due to lack of access to satellite navigation systems (e.g. the Global Positioning System, GPS): an AUV typically proceeds for long time intervals only relying on the measurements of its on-board sensors, without any communication with the outside environment. In this context, the filtering algorithm for the estimation of the AUV state is a key factor for the performance of the system; i.e. the filtering algorithm used to estimate the state of the AUV has to guarantee a satisfactory underwater navigation accuracy. In this paper, the authors present an underwater navigation system which exploits measurements from an Inertial Measurement Unit (IMU), Doppler Velocity Log (DVL) and a Pressure Sensor (PS) for the depth, and relies on either an Extended Kalman Filter (EKF) or an Unscented Kalman Filter (UKF) for state estimation. A comparison between the EKF approach, classically adopted in the field of underwater robotics and the UKF is given. These navigation algorithms have been experimentally validated through the data related to some sea tests with the Typhoon class AUVs, designed and assembled by the Department of Industrial Engineering of the Florence University (DIEF) for exploration and surveillance of underwater archaeological sites in the framework of the THESAURUS and European ARROWS projects. The comparison results are significant as the two filtering strategies are based on the same process and sensors models. At this initial stage of the research activity, the navigation algorithms have been tested offline. The presented results rely on the experimental navigation data acquired during two different sea missions: in the first one, Typhoon AUV #1 navigated in a Remotely Operated Vehicle (ROV) mode near Livorno, Italy, during the final demo of THESAURUS project (held in August 2013); in the latter Typhoon AUV #2 autonomously navigated near La Spezia in the framework of the NATO CommsNet13 experiment, Italy (held in September 2013). The achieved results demonstrate the effectiveness of both navigation algorithms and the superiority of the UKF without increasing the computational load. The algorithms are both affordable for online on-board AUV implementation and new tests at sea are planned for spring 2015.

Parallel Articulated-Cable Exercise Robot (PACER): Novel Home-Based Cable-Driven Parallel Platform Robot for Upper Limb Neuro-Rehabilitation

This paper examines the design, analysis and control of a novel hybrid articulated-cable parallel platform for upper limb rehabilitation in three dimensional space. The proposed lightweight, low-cost, modular reconfigurable parallel-architecture robotic device is comprised of five cables and a single linear actuator which connects a six degrees-of-freedom moving platform to a fixed base. This novel design provides an attractive architecture for implementation of a home-based rehabilitation device as an alternative to bulky and expensive serial robots. The manuscript first examines the kinematic analysis prior to developing the dynamic equations via the Newton-Euler formulation. Subsequently, different spatial motion trajectories are prescribed for rehabilitation of subjects with arm disabilities. A low-level trajectory tracking controller is developed to achieve the desired trajectory performance while ensuing that the unidirectional tensile forces in the cables are maintained. This is now evaluated via a simulation case-study and the development of a physical testbed is underway.

Robotic Neuromuscular Facilitation for Regaining Neural Activation in Hemiparetic Limbs

This paper introduces an effective engineered rehabilitation system for understanding and inducing functional recovery of hemiparetic limbs based on the concept of timing-dependent induction of neural plasticity. Limb motor function is commonly impaired after neurologic injury such as stroke, with hemiparesis being one of the major impairments. In an emerging unique intervention for hemiparesis, named repetitive facilitation exercise, or RFE, a therapist manually applies brief mechanical stimuli to the peripheral target muscles (e.g., tapping, stretching of tendon/muscle) immediately before a patient intends to produce a movement with the muscle. The practice of this rehabilitation procedure by a skilled therapist often leads to dramatic rehabilitation outcomes. However, unskilled therapists, most likely due to the inaccuracy of the timing of peripheral stimulation in reference to the intention of movement (i.e. motor command), are unable to recreate the same rehabilitation results. Robotic rehabilitation, on the other hand, can improve the reliability and efficacy of the operation by satisfying the timing precision required by the therapy. This study demonstrates the use of a pneumatically-driven MRI-compatible robot for RFE assessment. The pressure dynamics of the system is studied for an accurate estimation on the time of response of the robot. The required temporal precision of the therapy is obtained and the use of the device is validated through experiments on a human subject.