Sharif Digital Repository

Lift path planning is a significant subtask in constructability analysis, sequencing, and scheduling of congested industrial modular projects, impacting project cost, and safety. Although intuitive lift planning is still prevalent among the practitioners, this manual process might be tedious and error-prone for hundreds of lifts. This research presents an automated lift path planning method for heavy crawler cranes in no-walk scenarios employing a robotics approach. This method treats the lifted object as a three-degree-of-freedom convex mobile robot with discretized rotational and continuous translational motions. The proposed resolution-complete method models the crane capacity chart,... 

Trolling mode atomic force microscopy (TR-AFM) can considerably reduce the liquid-resonator interaction forces, and hence, has overcome many imaging problems in liquid environments. This mode increases the quality factor (QF) significantly compared with the conventional AFM operation in liquid; therefore, the duration to reach the steady-state periodic motion of the oscillating probe is relatively high. As a result, utilizing conventional imaging techniques, which are based on measuring the amplitude and phase, are significantly slower when compared to our proposed method. This research presents a high-speed scanning technique based on an estimation law to obtain the topography of various... 

The tension leg platform (TLP) is comprised of a buoyant hull that holds the platform’s topside. A group of tendons under the columns connect the TLP to the foundation. The TLP is displaced in six degrees of freedom due to environmental loads. Tendons moor the TLP in vertical direction (heave and pitch). Surge amplitude (horizontal displacement) of TLP is greater than other degrees of freedom. Also heave motion is coupled with surge one. Therefore, it is important to introduce and implement a method to control and reduce displacement of the TLP in horizontal direction. In this paper, a passive control system (double horizontal tuned mass damper (TMD)) is used to mitigate the surge motion of... 

In this research, important parameters of a rack and pinion steering system in dynamic steady state and transient responses have been investigated. For this purpose, virtual model of a medium passenger car in ADAMS/Car has been used. The model has up to 121 kinematic degree of freedom and includes all components of the rack and pinion steering system. Several different experimental test results have confirmed the validity of the model. Sensitivity analysis have been done based on design of experiments (DOE) method. Two level fractional factorial designs have been selected for this purpose. Steady state cornering and step steer input are the analysis that used for this research. Understeering... 

Dynamic behavior of a laminated composite beam (LCB) supported by a generalized Pasternak-type viscoelastic foundation, subjected to a moving two-degree-of-freedom (DOFs) oscillator with a constant axial velocity is studied. Analytical solution using the Galerkin method is sought and the couplings of the bending-tension, shear-tension, and bending-twist with the Poisson effect are considered. The possible separation of the moving oscillator from LCB during the course of motion is investigated by monitoring the contact force between the oscillator and LCB. The effects of the non-rigid foundation, oscillator parameters, and the load speed on the separation are also studied. It is found that... 

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows... 

New methods for the Inverse and forward kinematic analysis of the novel six Degrees of Freedom (6DOF) parallel manipulator which has only two legs are presented. The actuation of the new mechanism is through two base-mounted spherical actuators. In the inverse pose kinematic, active joint variables are directly calculated with no need for the evaluation of passive joint variables. In the forward pose kinematic, closed form solution adopting a new approach is presented. It is shown that the inverse and forward pose kinematic have sixteen and four different solutions, respectively. Moreover, closed form equations for the rate kinematic analysis are proposed. Finally, two different categories... 

In this paper, we propose a new 6-DOF parallel mechanism. Due to the fact that degrees of freedom in this robot outnumber the number of kinematic chains, it is not a fully parallel mechanism. This results in a weight and inertia reduction and better dynamic performance, making it ideal for haptic and pole climbing applications. The fact that the mechanism is open on one side enable it to wrap around a pole from one side minimizing the center of gravity distance from the pole and the resulting gripping moments. Both inverse and forward Kinematic and dynamic analysis of the proposed mechanism is addressed. Workspace of the mechanism is compared to that of the Stewart's mechanism and the... 

In this article, impedance control of a two link flexible link manipulators is addressed. The concept of impedance control of flexible link robots is rather new and is being addressed for the first time by the authors. Impedance Control provides a universal approach to the control of flexible robots, in both constrained and unconstrained maneuvers. The initial part of the paper concerns the use of Hamilton's principle to derive the mathematical equations governing the dynamics of joint angles, vibration of the flexible links and the constraining forces. The approximate elastic deformations are then derived by means of the Assumed-Mode-Method (AMM). Using the singular perturbation method, the... 

Wall walking robots are designed for different purposes, rescue operations, wall inspections and jobs such as painting and cleaning and fire fighting for tall buildings. These are some cases that these types of robots are extensively used. This paper describes a design of a new serial mechanism for wall climbing job. In deed we are seeking to define a minimum degree of freedom mechanism to be applied in a robot moving vertically on a surface. This mechanism has 5 links, but at any point it works with its 4 links, actually in each cycle of motion the linkage will be interchanged. Copyright © 2006 by ASME  

In this article a new technique for the dynamic response of structures is investigated. This applied procedure can predict the approximate seismic performance of the structures and it is fast, inexpensive and results are reasonably acceptable. In fact, this novel method logically combines two different techniques, 'incremental dynamic analysis (IDA)' and 'modal pushover analysis (MPA)', presented by other researchers. This method will take advantage of both methodical ideas such as equivalent single degree of freedom of multi-degree structures and the implementation of different scaled level of an earthquake record to the provided equivalent SDF structure. Using this procedure, simple... 

This paper presents an approach to improve the sliding mode controller performance. Accordingly, a fuzzy controller is designed based on a limited number of rules and independent of the sliding mode controller complexity. To enhance the performance, this controller will continuously optimize the sliding mode controller parameters including hitting control gain, boundary layer thickness, sliding surface slope and intercept. The controller is applied to a two-degree-of-freedom robot and the experimental results are compared with a QFT based and a PID controller. The results demonstrate the significant performance improvement of the proposed controller. © 2005 IEEE  

In some tasks, a rigid robot manipulator handles a long, slender, and flexible tool, which usually has not been equipped with vibration measuring devices. This situation makes a different tool tip position control problem. In this paper, a new method will be presented for simultaneous tip position and vibration suppression control of a flexible tool on a rigid-link 3-DOF robot. This approach uses fuzzy logic rule-based controllers without using any sensors and actuators on the tool or a priori knowledge about the tool. Numerical simulation of robot and tool set has been accomplished and results support the fact that designed fuzzy controllers perform remarkably well in reducing vibrations... 

In this article kinematic analysis of a 3 Leg-Spherically Actuated (3SA) parallel manipulator will be addressed. Since each leg has a spherical actuator (three inputs for each leg) and manipulator has three legs; totally, there are nine inputs. Due to the fact that the manipulator has six degree of freedom, only six independent inputs are needed. Thus actuation could be done in different ways. If the triangles representing base and platform are equilateral, there are twenty different ways of actuation that should be studied during forward kinematic analysis. Rather than adopting the standard Denavit-Hartenberg approach, a simple method for forward kinematic analysis for all these different... 

Stability analysis of machine tool requires determining of frequency response function (FRF) of spindle. Since this response is changed with a change of tool, Receptance coupling sub-structuring analysis may be used to couple the tool and spindle FRFs. A major difficulty in this regard is the determination of joint model between the two sub-structures. In particular, the identification of rotational DOFs at joints is difficult. In this research, a joint model which accounts for rotational DOFs is proposed and verified which does not require any rotational DOF measurement on machine tool. An optimization method based on genetic algorithm is employed to find parameters of the joint model.... 

Structures with inappropriate distributions of strength and stiffness have performed poorly in recent earthquakes, and most of the observed collapses have been related to some extent to configuration problems or a wrong conceptual design. Shear building models of multi-story structures are considered in this study and are subjected to a group of severe earthquakes. It is shown that the strength distribution patterns suggested by the seismic codes do not lead to a uniform distribution and minimum amount of ductility, drift, and damage. A new pattern is proposed that is a function of the period of the structure and the target ductility. An iterative approach is also developed to determine the... 

In this paper an effective approach for kinematic and dynamic modeling of high mobility wheeled mobile robots (WMR) has been presented. As an example of these robots, the method has been applied on CEDRA rescue robot which is a complex, multibody mechanism. The model is derived for 6-DOF motions enabling movement in x, y, z directions, as well as pitch, roll and yaw rotations. Forward kinematics equations are derived using Denavit-Hartenberg method and the wheels Jacobian matrices. Moreover the inverse kinematics of the robot is obtained and solved for the wheel velocities and steering commands in terms of desired velocity, heading and measured link angles. Finally dynamical analysis of the... 

Two-degree-of-freedom (2-DOF) electrical machines require position sensors for their motion control. In comparison with using two independent sensors, using a 2-DOF sensor enhances the closed-loop control system's performance. However, due to the 3-D structure of the 2-DOF sensor, its performance evaluation needs 3-D analysis. Also, due to helical motion the accuracy deterioration of the sensor, under mechanical faults needs more attention. Although the finite element method (FEM) is the best way to simulate such sensors, most of the commercial packages for transient finite element simulations are not able to consider two separate motions simultaneously. Furthermore, FEM has a high...