Control of an Aerial Manipulator With an On-Board Balancing Mechanism

Multirotor Unmanned Aerial Systems (UAS) are highly mobile in flight and possess stable hovering capabilities. Because of their unique flight characteristics, the utilization of the platform for active tasks such as aerial manipulation is highly attractive. Much work has been done in recent years towards the implementation of multirotor for aerial manipulation, however, progress in the field has been slow due to the many challenges involved in the implementation of robust rotor control. In an attempt to reduce the effects of the manipulator, a technique for disturbance rejection using a novel balancing mechanism is proposed. In this paper, the dynamic equations of a coupled multirotor and manipulator are analyzed as a single body for use in the attitude control of the platform. By mounting the mechanism, the platform effectively gains marginal control over the positioning of its center of gravity relative to a body fixed frame. It can be shown that the increased mobility can be utilized to reduce rotor saturation for any given flight condition and improve the effectiveness of previously developed rotor control methods.

Analysis of Deep Sea Umbilical in Steep Wave Configuration

Deep sea mining is mineral retrieval process that takes place on the ocean floor wherein global industries are actively exploring and experimenting of different techniques in this relatively new concept of mining for extracting it economically from depths of 5000–5500 m below the ocean’s surface. National Institute of Ocean Technology (NIOT), India has been working on a mining concept for ∼6000 m water depth where a crawler based mining machine collects, crushes and pumps nodules to the mother ship using a positive displacement pump through a flexible riser (umbilical) system. The umbilical also serve as the weight supporting member for the miner and pump. In this paper, static and dynamic analysis of the umbilical system in steep wave configuration and the miner is carried out using ORCAFLEX for launching and touchdown conditions. Three different materials are considered and the best suitable material for umbilical is selected as the first step based on the tension. Then umbilical with Single Miner System is analyzed for the launching and touchdown conditions. Based on the analysis the optimum number and spacing of buoyancy tanks that will keep the stresses within the allowable limits in the umbilical cable are recommended.

Experimental and Simulation of a Cam and Translated Roller Follower Over a Range of Speeds

In this study a cam and follower mechanism is analyzed. There is a clearance between the follower and the guide. The mechanism is analyzed using SolidWorks simulations taking into account the impact and the friction between the roller follower and the guide. Four different follower guide’s clearances have been used in the simulations like 0.5, 1, 1.5, and 2 mm. An experimental set up is developed to capture the general planar motion of the cam and follower. The measures of the cam and the follower positions are obtained through high-resolution optical encoders (markers). The effect of follower guide’s clearance is investigated for different cam rotational speeds such as 100, 200, 300, 400, 500, 600, 700 and 800 R.P.M. Impact with friction is considered in our study to calculate the Lyapunov exponent. The largest Lyapunov exponents for the simulated and experimental data are analyzed and selected.

Adaptive Gimbal Control Approach to Account for Power Consumption and Landmark Tracking Quality

Unmanned Aerial Vehicles (UAV) are commonly used for robotics research and industrial purposes. Most of the autonomous applications use visual sensors and inertial measurement units for localization. Design constraints of such systems are defined considering smooth operation requirements such as indoor environments without external forces where input tracking signal is constant during an operation. In this research paper, we simultaneously investigate and compare stability, power consumption and landmark tracking quality of a visual sensor mounted gimbal specifically for rapid UAV motion requirements where input signal continuously varies such as at obstacle rich environments. We not only attempt to find efficient control parameters but also compare these settings with power consumption and landmark tracking quality metric which are vital for mobile robots and localization algorithms. Efficiency of the system response is analyzed with rise and settling time as well as oscillation amplitude and frequencies. These parameters are tested and benchmarked with various voltage and current limitations. In addition to that, different response behaviors were investigated considering landmark tracking quality metrics including feature detection and image blur. We have shown that gimbal stabilization controller under continuously varying input signal requires less responsive behavior to keep landmark tracking accuracy stable. Initial simulation results, system development and experimental setup procedure are explained and behavior plots for each topic are listed and analyzed.

Surface Roughness Identification in End Milling Using Vibration Signals and Fuzzy Clustering

The study presented involves the identification of surface roughness in Aluminum work pieces in an end milling process using fuzzy clustering of vibration signals. Vibration signals are experimentally acquired using an accelerometer for varying cutting conditions such as spindle speed, feed rate and depth of cut. Features are then extracted by processing the acquired signals in both the time and frequency domain. Techniques based on statistical parameters, Fast Fourier Transforms (FFT) and the Continuous Wavelet Transforms (CWT) are utilized for feature extraction. The surface roughness of the machined surface is also measured. In this study, fuzzy clustering is used to partition the feature sets, followed by a correlation with the experimentally obtained surface roughness measurements. The fuzzifier and the number of clusters are varied and it is found that the partitions produced by fuzzy clustering in the vibration signal feature space are related to the partitions based on cutting conditions with surface roughness as the output parameter. The results based on limited simulations are encouraging and work is underway to develop a larger framework for online cutting condition monitoring system for end milling.

High-Precision Tracking Control of Machine Tool Feed Drives Based on ADRC

In this paper, the active-disturbance-rejection control (ADRC) is applied to realize the high-precision tracking control of CNC machine tool feed drives. First, according to the number of the feedback channel, the feed systems are divided into two types: signal-feedback system, e.g., linear motor and rotary table, and double-feedback system, e.g., ball screw feed drive with a load/table position feedback. Then, the appropriate controller is designed to ensure the closed-loop control performance of each type of system based on the idea of ADRC. In these control frameworks, the extended state observers (ESO) estimate and compensate for unmodeled dynamics, parameter perturbations, variable cutting load, and other uncertainties. For the signal-feedback system, the modified ADRC with an acceleration feedforward term is used directly to regulate the load/table position response. However, for the double-feedback system, the ADRC is applied only to the motor position control, and a simple PI controller is used to achieve the accurate position control of the load. In addition, based on ADRC feedback linearization, a novel equivalent-error-model based feedforward controller is designed to further improve the command following performance of the double-feedback system. The experimental results demonstrate that the proposed controllers of both systems have better tracking performance and robustness against the external disturbance compared with the conventional P-PI controller.

Robotic Gripper for Payload Capture in Low Earth Orbit

The consensus to a study phase for an IXV (Intermediate eXperimental Vehicle) successor, a preoperational vehicle called PRIDE (Programme for Reusable In-orbit Demonstrator in Europe), has been recently enlarged, as approved during last EU Ministerial Council. One of the main project task consists in developing PRIDE to conduct on orbit servicing activity with no docking. PRIDE would be provided with a robotic manipulator system (arm and gripper) able to transfer payloads, such as scientific payloads, from low Earth orbiting platforms to PRIDE payload bay. The platform is a part of a space tug designed to move small satellites and other payloads from Low Earth Orbits (LEO) to Geostationary orbit (GEO) and viceversa. A study on this robotic technology is here presented. This research is carried out by Politecnico di Torino and Thales Alenia Space Italy (Grasping Manipulator Design), and by Thales Alenia Space Italy and Amet (PRIDE Robotics System Design). The system configuration of the robotic manipulator is first described in terms of volumes and masses. The assumed housing payload bay requirements in terms of volume (<100 l) and mass (<50 kg) combined with the required overall arm dimensions (4 m length), as defined following the stated mission scenario, and mass of the payload (5–30 kg) force to developing an innovative robotic manipulator with the task-oriented end effector. It results in a 7 degree-of-freedom arm to ensure a high degree of dexterity and a dedicate end-effector designed to grasp the payload interface. The gripper concept here developed consists in a multi-finger hand able to lock both translational and rotational payload degrees of freedom through an innovative under actuation strategy to limit its mass and volume. While in the literature in usual actuation architectures, underactuated systems have been realized where the first (nearest) phalanx closure led afterwards to the closure of the second (distal) one using the loading of a torsional springs and mechanical linkages, this system presents a new underactuation strategy. In this case the distal phalanx closes before the nearest one, allowing to grasp the handle side and limiting the handle length and volume. This concept will allow the distal phalanx to move independently from the nearest one. A configuration study on the payload handle interface has also been performed. Moreover, trade-off studies, computer aided design models, multibody and structural analysis of the whole system are shown to prove its feasibility. Finally, the concept of system control architecture, organized in three main blocks is defined: the Control Overall System Block, the Control Arm Block and the Control Robotic Hand Block.

Mechatronic Design of a Mixed Conventional/Braking Actuation Mobile Robot

This paper presents the design of a novel mixed conventional/braking actuation mobile robot (MAMR), which replaces conventional actuators used for steering with controllable brakes. The mechatronic design of a novel electromechanical braking actuator, its implementation in the MAMR, and the mechatronic design of the MAMR are presented. A motion experiment is also given as a demonstration. The MAMR presented in this paper implements a new platform for mobile robots which is composed of two electromechanical braking actuators and an omni-directional drive wheel. The electromechanical brake presented is an omni-directional ball transfer that is electronically lockable. When the brake is in the locked state, it generates a reactive friction force onto a dynamic system that, in the case of the MAMR, can be used to steer and brake. This platform offers a minimalistic approach to locomotion in mobile robots.

Nonlinear Reduced-Order Models for Aerodynamic Lift of Oscillating Airfoils

For the present study, setting Strouhal Number as the control parameter, we perform numerical simulations for the flow over oscillating NACA-0012 airfoil at Reynolds Number 103. Temporal profiles of the unsteady lift, and their respective spectra clearly indicate the solution to be a period-1 attractor for low Strouhal numbers. This study reveals that aerodynamic forces produced by the oscillating airfoils are independent of the initial kinematic conditions that proves existence of the limit cycle. Frequencies present in the oscillating lift force are composed of the fundamental harmonics, and its odd harmonics. Using these numerical simulations, we observe the shedding frequencies nearly equal to the excitation frequencies in all the cases. Hence, considering it as a primary resonance case, we model the unsteady lift force through a modified van der Pol oscillator. Using the method of multiple scales and spectral analysis of the steady-state CFD solutions, we estimate the frequencies and the damping terms in the reduced-order model. We prove the applicability of this model to all the planar motions of airfoil; heaving, pitching and flapping. With the increasing Strouhal number, the nonlinear damping terms for all types of motion approach similar magnitudes. Another important aspect in one of the currently-proposed model is capturing the time-averaged value of the aero-dynamic lift force.

Varied System Geometry and Noise Implementation Applied to Nonlinear Model Tracking

The following is a study in nondestructive health monitoring wherein the physical system being studied is excited near resonance and mapped through its transition from health to failure. The system studied is a slender cantilever beam excited near its second natural frequency. For this study, no damage is initiated and so it comes in contrast to the more common techniques where the damage type and location allow for an element of control in instrumentation and analysis. The method implemented allows for health monitoring in situ, so it does not require stopping the event to do system testing, as is the case for many common approaches. Moreover, this method, implements a nonlinear model of the physical system, avoiding false flags that can be problematic for linear-based methods when applied to systems demonstrating healthy nonlinear behavior. The method, known as Nonlinear Model Tracking (NMT) uses a theoretical model of the system that includes a cubic nonlinear stiffness term. Experimentally, stimulus and response data are collected and used in Continuous Time-based system identification to estimate the system’s nonlinear stiffness coefficient. Harmonic fitting to the two recorded data sets allow for robust performance in the presence of noise and variations in the system geometry show that, even in cases where the nonlinear model is not accurate for the system being studied, the method works consistently. In many of the tests the method gives premonition of failure hours in advance, which would in many real world scenarios, gives users time to react safely. This study focusses particularly on varying inputs to the system and attempting to map changes in parameter estimation to stages of damage.