Polarization image laser line extraction methods for reflective metal surfaces

In this work, we propose a novel pipeline method for laser line extraction from images with a polarization image sensor. The proposed method is specially developed for strong laser beam reflections from metal surfaces. For the pre-processing stage, we propose a demosaicing algorithm for color polarizer filter array (CPFA) sensors. This can be implemented by using either one quarter or full resolution of the sensor. In addition, we propose two methods for optimizing the information available in a 12-channel color polarization image: The first method, is based on the minimum linearly polarized irradiance, and the second method, is based on the linear polarization intensity. These pre-processing, and optimization methods are combined with laser line extraction methods. The laser line extraction is done with either the Polarized Finite Impulse Response (FIR) Center Of Gravity (COG), where the laser line coordinates are computed from the filtered laser intensity distribution, or with the Polarized FIR-Peak, where the laser line coordinates are calculated from the first derivative of the filtered laser signal. The performance of the proposed algorithms is studied experimentally using a laser line scanner assembly, made of a polarization camera, and a laser line projector operating in the blue wavelength range.acceptedVersio

Vision-based control of a knuckle boom crane with online cable length estimation

A vision-based controller for a knuckle boom crane is presented. The controller is used to control the motion of the crane tip and at the same time compensate for payload oscillations. The oscillations of the payload are measured with three cameras that are fixed to the crane king and are used to track two spherical markers fixed to the payload cable. Based on color and size information, each camera identifies the image points corresponding to the markers. The payload angles are then determined using linear triangulation of the image points. An extended Kalman filter is used for estimation of payload angles and angular velocity. The length of the payload cable is also estimated using a least squares technique with projection. The crane is controlled by a linear cascade controller where the inner control loop is designed to damp out the pendulum oscillation, and the crane tip is controlled by the outer loop. The control variable of the controller is the commanded crane tip acceleration, which is converted to a velocity command using a velocity loop. The performance of the control system is studied experimentally using a scaled laboratory version of a knuckle boom crane

Robotic weld groove scanning for large tubular T-joints using a line laser sensor

This paper presents a novel procedure for robotic scanning of weld grooves in large tubular T-joints. The procedure is designed to record the discrete weld groove scans using a commercially available line laser scanner which is attached to the robot end-effector. The advantage of the proposed algorithm is that it does not require any prior knowledge of the joint interface geometry, while only two initial scanning positions have to be specified. The position and orientation of the following scan are calculated using the data from two previous weld groove scans, so once initiated, the scanning process is fully autonomous. The procedure is a two-step algorithm consisting of the prediction and correction substeps, where the position and orientation of the sensor for the following scan are predicted and corrected. Such a procedure does not require frequent weld groove scanning for navigation along the groove. The performance of the proposed procedure is studied experimentally using an industrial-size T-joint specimen. Several cases of scanning motion parameters have been tested, and a discussion on the results is given.publishedVersio

Determination of constraint forces for an offshore crane on a moving base

In this paper we propose an efficient method for calculating the forces of constraints in an open-chain multibody system, like a robot mounted on a vehicle with 6 degrees of freedom. The dynamical model is based on Kane's equation of motion, where screw theory is used to calculate the projection matrices from the link twists of the multibody system. This leads to a general modeling procedure relying on screw transformations that is presented in the paper. The procedure for determination of the constraint forces is given as an extension of the dynamical model and can be implemented after the equations of motion have been formulated and solved. We implement the described method for the specific case of a vessel with a heavy crane, and provide the simulation results. The method provides a basis for future work on the detailed modeling of friction in the joints of serial link mechanisms, and on the evaluation of potential fatigue consequences of different control solutions

Dynamic modelling and force analysis of a knuckle boom crane using screw theory

This article presents a method for determination of dynamic reaction forces in knuckle boom cranes. The method is based on the dynamic modelling procedure, which is an extension of Kane’s equations of motion. An efficient formulation is used, where the link velocities and angular velocities are given in terms of the link twists, which makes it straightforward to describe the partial velocities and partial angular velocities as joint lines given as screws in Plücker coordinates. The method is presented in a systematic and general manner and is applicable for spatial crane-like manipulators with passive rotary joints and piston actuators. We propose a procedure for the substitution of the actual actuator wrenches with an equivalent set of wrenches applied on the actuator supports, which leads to an efficient procedure for the determination of reaction forces in passive joints. The application of screw theory to dynamic modelling and force analysis leads to an elegant and geometrically meaningful formulation. The method is implemented for a knuckle boom crane and simulation results are provided. The determined reaction forces can be used in mechanical problems as structural integrity calculations and fatigue lifetime prediction, as well as in control problems involving dry friction.publishedVersion© 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.(http://creativecommons.org/licenses/by/4.0/

Kinematics and Dynamics of Flexible Robotic Manipulators Using Dual Screws

In this article, we present a new procedure for the derivation of the linearized kinematics and dynamics of a flexible industrial robotic manipulator. We introduce the Lie groups of dual rotation and dual homogeneous transformation matrices, which are the basis for the derivation of dual twists. In addition, dual screws and dual screw transformation matrices are introduced, which are used for the development of a general and systematic linearization procedure for both kinematics and dynamics. This leads to expressions that are linearized in all the states associated with the elastic motion. The dynamic modeling procedure is based on Kane’s method, where the partial velocities and partial angular velocities are given as dual screws arranged as columns of dual projection matrices. The elasticity of the links is modeled by the assumed mode method. The presented procedure is implemented numerically for a 4-degrees of freedom manipulator and the simulation results are given

Determination of constraint forces for an offshore crane on a moving base

In this paper we propose an efficient method for calculating the forces of constraints in an open-chain multibody system, like a robot mounted on a vehicle with 6 degrees of freedom. The dynamical model is based on Kane's equation of motion, where screw theory is used to calculate the projection matrices from the link twists of the multibody system. This leads to a general modeling procedure relying on screw transformations that is presented in the paper. The procedure for determination of the constraint forces is given as an extension of the dynamical model and can be implemented after the equations of motion have been formulated and solved. We implement the described method for the specific case of a vessel with a heavy crane, and provide the simulation results. The method provides a basis for future work on the detailed modeling of friction in the joints of serial link mechanisms, and on the evaluation of potential fatigue consequences of different control solutions.acceptedVersion© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other work

Digital Twin Based Condition Monitoring of a Knuckle Boom Crane: an Experimental Study

This paper presents a novel approach for implementation of a digital twin for condition monitoring of a small-scale knuckle boom crane. The digital twin of the crane is simulated real-time in a nonlinear finite element (FE) program, where the estimated payload weight is used as an input. We implement an inverse method for estimation of the weight as well as its force vector direction based on physical strain gauge measurements. Additional strain gauges were utilized for validation of accuracy of the digital twin and inverse method. Based on a few physical sensor outputs, the digital twin allows for real-time determination of stresses, strains and loads at an unlimited number of hot spots. Therefore a digital twin can be an effective tool for predictive maintenance and product life-cycle management. In addition, condition monitoring of cranes during heavy-lift operations increases safety and reliability. The presented approach is described in a general manner and is applicable for various robotic manipulators used in the industry

Dynamics of luffing motion of a flexible knuckle boom crane actuated by hydraulic cylinders

In this paper we present a modeling procedure for a flexible knuckle boom crane, which is actuated by hydraulic cylinders and is modeled as a planar multibody system. We propose a convenient framework where both rigid body velocities and velocities caused by flexible behavior are represented as twists. Such formulation allows for using screw transformations, which leads to systematic derivations. Dynamics of a crane and mass balance of hydraulic cylinders are coupled using the bond graph method. In addition, we present a procedure for the determination of reaction forces in passive joints, which is conveniently given as an extension of the dynamic modeling procedure. Both procedures are presented in a general and systematic manner such that they can be applied for a group of planar flexible manipulators. We study the dynamics of luffing motion of a crane by numerical simulation and provide the simulation results, as well as determine the reaction forces in passive joints. The simulation results are validated by the ANSYS finite element analysis. The derived model provides a basis for design of luffing cylinders and can potentially be used for studying performance of a crane control system