Fractional-order kinematic analysis of biomechanical inspired manipulators

Present-day mechanical manipulators reveal limited performances when compared with the human arm. Joint-driven manipulators are sub-optimal due to the high actuator requirements imposed by the transients of the operational space tasks. Muscle-actuated arms are superior because the anatomic structures adapt the task requirements to the driving linear actuators. However, the advantages of muscle actuation are difficult to unravel using the standard integer-order kinematics based on the integer derivatives, namely the positions, velocities and accelerations. This paper investigates the human arm and evaluates the influence of biomechanics upon the driving actuators by means of a new method of kinematic analysis and visualisation. The proposed method uses the tools of fractional calculus for computing the continuous propagation of the signals between positions and accelerations. The behaviour of the variables is compared in the joint and muscle spaces, using both the kinematics in the time domain and the describing function method. In this line of thought, the classical integer-order kinematics, with three discrete levels of visualisation, is generalised to a continuous description represented by the fractional-order kinematics.

Solving nonlinear optimal path tracking problem using a new closed loop direct–indirect optimization method: application on mechanical manipulators

SUMMARYThe purpose of this study is to determine the dynamic load carrying capacity (DLCC) of a manipulator that moves on the specified path using a new closed loop optimal control method. Solution methods for designing nonlinear optimal controllers in a closed-loop form are usually based on indirect methods, but the proposed method is a combination of direct and indirect methods. Optimal control law is given by solving the nonlinear Hamilton–Jacobi–Bellman (HJB) partial differential equation. This equation is complex to solve exactly for complex dynamics, so it is solved numerically using the Galerkin procedure combined with a nonlinear optimization algorithm. To check the performance of the proposed algorithm, the simulation is performed for a fixed manipulator. The results represent the efficiency of the method for tracking the pre-determined path and determining the DLCC. Finally, an experimental test has been done for a two-link manipulator and compare with simulation results.

Review of robotic manipulators and identification of the main problems

One of the main elements of automation of industrial enterprises is the use of robotic systems consisting of mechanical manipulators and control systems. In recent years, the market of service robotics has been actively developing. The main part of the market of professional service robots in value terms is occupied by medical devices. Agriculture and logistics are also actively developing areas. The success of the automation systems implementation depends on the solution of complex scientific and technical problems, primarily in the following areas: machine vision; sensor networks; navigation systems. Thus, one of the fundamental problems, the solution of which largely depends on the success in creating the perfect adaptive and intelligent robots, is the use of such types of sensors of sensory information, which allow obtaining a sufficiently large amount of information about the problem environment in a short time. This is a problem of creating means of perception.

OPTO-ACOUSTIC DATA FUSION FOR SUPPORTING THE GUIDANCE OF REMOTELY OPERATED UNDERWATER VEHICLES (ROVs)

Remotely Operated underwater Vehicles (ROVs) play an important role in a number of operations conducted in shallow and deep water (e.g.: exploration, survey, intervention, etc.), in several application fields like marine science, offshore construction, and underwater archeology. ROVs are usually equipped with different imaging devices, both optical and acoustic. Optical sensors are able to generate better images in close range and clear water conditions, while acoustic systems are usually employed in long range acquisitions and do not suffer from the presence of turbidity, a well-known cause of coarser resolution and harder data extraction. In this work we describe the preliminary steps in the development of an opto-acoustic camera able to provide an on-line 3D reconstruction of the acquired scene. Taking full advantage of the benefits arising from the opto-acoustic data fusion techniques, the system was conceived as a support tool for ROV operators during the navigation in turbid waters, or in operations conducted by means of mechanical manipulators. <br><br> The paper presents an overview of the device, an <i>ad-hoc</i> methodology for the extrinsic calibration of the system and a custom software developed to control the opto-acoustic camera and supply the operator with visual information.