INTERNATIONAL JOURNAL OF ROBOTICS
Year:2009 | Volume:1 | Issue:1|Papers Count:7

This paper describes a virtual reality (VR)-assisted robotic surgery simulator for bone surgery training. A trainee surgeon holds the haptic robot stylus and manipulates it three dimensionally to interact with the virtual bone. The robotic simulator allows the trainee surgeon to feel the machining force and to see the bone removal in real-time. To make the virtual world feel real, this work incorporates a physics-based force model of bone machining process to calculate tool-bone interaction forces. The physics-based model considers chip formation process and includes main machining parameters such as feed rate and tool geometry. Real-time force feedback is provided to the user via a fast voxel-based collision detection and response algorithm. A multi-rate haptic rendering approach is used to interpolate forces between consecutive updates and to send force commands to the haptic robot at a sufficiently high-rate. A volumetric visual rendering technique is also described to display the bone volume and removal of bone material during machining. The simulator utilizes voxel information from bone CT scan of real patients. The real-time implementation of the method in a dental training simulator is described using a 6-DOF haptic robot. Virtual machining force results are presented for a surface machining operation.

In the present paper the dynamics of a 3DoF motion platform is studied that introduces a novel design of this mechanism. In this design, a balancer module which provides a non rotating vertical movement for the platform is utilized. It consists of three pairs of scissors which are synchronized by a gear set and a vertically mounted pneumatic actuator which balances the static weight of the platform. The specification of this mechanism compared to the previous designs is that it provides a nearly constant upward force that remains in the direction of the weight in entire the workspace. Additionally it leads to a linear damping force in heave motion which provides a better control task. In this paper the complete dynamics of the system is modeled where factors like actuator frictions and non-uniform distribution of load and the mass and inertia of legs are also considered and the velocity analysis is performed. The accuracy of the obtained dynamics model is verified by comparing the result of simulation with that of an equivalent model built in SimMechanics.

In this paper, design and manufacturing of a mobile mechanical manipulator with flexible joints are presented. Ergonomic principals such as balancing the human height and anthropometric, enough space for moving, accessibility of the controllers, making environment labor-friendly adapting the manipulator with the load and anthropometric are considered in order to reduce harm and fatigue. First, the kinematics and dynamic equations of the mechanism with flexible joints for the three major axis of the mobile robot are derived and simulated. Next, a method for determination of the dynamic load carrying capacity (DLCC) for a specific reference is explained subject to both accuracy and actuator constraints. The manipulator is tested for a given trajectory in order to find the characteristics of the designed manipulator. While the manipulator is designed to carry the maximum load, end-effector’s speed, robot's compatibility with the operator's condition, and accuracy are the most important applicable points of the manipulator. Therefore, the manipulator in different trajectories with various speeds and loads are tested, and then the results are analyzed.

Optimal design of parallel manipulators is known as a challenging problem especially for cable driven robots. In this paper, optimal design of cable driven redundant parallel manipulators (CDRPM) is studied in detail. Visual Inspection method is proposed as a systematic design process of the manipulator. A brief review of various design criteria shows that the optimal design of a CDRPM cannot be performed based on single objective. Therefore, a multi objective optimal design problem is formulated in this paper through an overall cost function. Furthermore, a proper weighting selection for the overall cost function is proposed, which can be viewed as a promising method to the open problem of parallel manipulator design. In order to verify the effectiveness of the proposed method, it is applied on the design of KNTU CDRPM, an eight actuated with six degrees of freedom CDRPM, which is under investigation for possible high speed and wide workspace applications in K.N. Toosi University of Technology. Finally, a combined numerical optimization algorithm is used to find the unique global optimum point. The result shows a significant enhancement in the performance characteristics of the KNTU CDRPM compared to that of the other CDRPMs. Since the proposed method is not restricted to any particular assumption on the objectives and design parameters, it can be used for optimal design of other manipulators.

In this paper, the problem of trajectory optimization of flexible space robots is considered and an efficient approach is proposed for solving it. The space robots are considered as mechanical manipulators having rigid and flexible links. The main duty of these robots is to translate a payload mass between two specified points. To derive dynamic model of these manipulators, their flexible links are assumed as a set of rigid links connected together. By adding strain potential energy to Lagrange equations, the flexible behaviour of flexible links is modeled with good accuracy. In present paper, the problem of trajectory optimization of space manipulators is defined based on minimum joint torque (minimum control effort) objective function. A new approach, that is a developed form of direct collocation method, is used for solving this problem. This new approach is based on simultaneous using of differential flatness to decrease dimensional space of the problem and B-spline curves to approximate trajectories. In this approach, state equations and path constraints are applied at specified time nodes and control points of B-spline curves are considered as optimization variables. In this approach, the problem of trajectory optimization is converted to a nonlinear programming problem and exactly solved by nonlinear programming methods. By using this approach, the numbers of optimization variables and constraints are significantly decreased and the possibility of online trajectory optimization is provided.

Mobile platforms with one or more manipulators are of great interest for their wide area of applications and dexterity. Including a suspension system in such mobile platforms will certainly add to their maneuverability, though causes more complexity. In this paper, a suspended mobile platform with two 6-DOF manipulators is used to manipulate an object in a mixed circular-straight path. The Multiple Impedance control (MIC) as a Model-Based algorithm, enforces the same impedance law both on the robotic system, and the manipulated object level. To apply model-based control laws, however, it is needed to extract system dynamics equations. For such highly nonlinear dynamical systems, it is necessary to have a concise set of dynamic equations with as few as possible mathematical calculations. Therefore, the concept of Direct Path Method, is extended to derive explicit dynamics modeling for such challenging systems. Then non-holonomic constraint of the wheeled platform is discussed, and obtained dynamics model is reformatted to become more concise using Natural Orthogonal Complement Method. Next, the MIC law is applied to cooperative manipulation of an object by the two manipulators. The obtained results reveal the success of the suspended mobile robot in its defined mission.

In this paper, a 3-axis motion simulator, as a three degree-of-freedom test stand for aircraft instrument testing and calibrating within a Hardware-In-The-Loop Environment, is studied for control analyses. A mathematical model of the simulator mechanical structure is derived and then linearized using Taylor series expansion around the instantaneous equilibrium point which is the aircraft time-dependant Euler angles and their rates. Also, the aircraft, earth and atmosphere are modeled in Matlab using Aerosim blocksets. A linear quadratic regulator (LQR) control law is developed to track the attitude, angular rates and angular acceleration of the Navion aircraft in a complicated maneuver. The control law is shown to be efficient in the presence of atmospheric turbulence, and robust to unknown bounded disturbances. The accuracy and correctness of the proposed control system is verified by the simulation.