عباس کرمی

In the present research, a three-degree-of-freedom haptic device was used to simulate a virtual object located on a point on a two-dimensional wall. Two spatial coordinates of the operating point on the wall were arbitrary. Therefore, the robot would have two degrees of freedom redundancy for this task. These two degrees of robot redundancy were specified by the artificial bee colony optimization and crow optimization algorithm in such a way that while ensuring the stability of the robot, the damping coefficient of the simulated virtual object was also maximized. The optimization process was performed in two different ways. In the first case, the stiffness of the robot was assumed to be a constant value in the whole workspace, while in the second case, the stiffness was considered a function of the robot configuration. In each case and at each operating point, first an effective mass, an effective damping coefficient, and an effective stiffness for the robot were obtained, and then using some theoretical relations, a stable operation boundary was obtained. Finally, the optimization methods specify the location of the operating point in such a way that the simulated damping coefficient was maximized. The results show that in the case of constant robot stiffness, both of the mentioned methods were able to simulate the maximum value of 1.825 for the virtual damping coefficient. However, in the case of variable robot stiffness, the crow and bee algorithms reached the values of 2502 and 2498, respectively as the maximum damping coefficient that could be simulated. In addition, although the number of cost function calculations is the same in both methods, the crow optimization algorithm was faster and more repeatable.

Haptic devices are the interface between real and virtual environment. Stability of a haptic device is a critical issue to insure human safety. Haptic devices generally have several degrees of freedom and complex dynamics. The complexity of this dynamic is due to the complicated mechanism along with the friction of Coulomb and viscous, which makes it difficult to study their stability in general conditions. These robots can cover a large workspace. While the robot stability during simulating a virtual object is significant, the range of motion of the stylus of the haptic device in this situation is limited. This has led to the use a 1-DoF dynamic to determine the robot's stable boundary. Meanwhile, there is no systematic approach for simplifying the model around the operating point. In this paper, a new method is used to obtain the simplified dynamics of the robot so that the nonlinear dynamics of the multi degrees of freedom haptic device can be simplified to a simple dynamic. Using this method, the stability of a KUKA LWR IV industrial robot (as a six-degree of freedom haptic device) in different configurations has been studied and the accuracy of the proposed method has been evaluated through simulations in MATLAB. In this research, manipulator multi-DOF dynamics is simplified to one-DOF dynamics with constant effective mass, viscous and Coulomb friction around the operational point. While stability and passivity analysis for the main manipulator is complex, the acquired one-DOF dynamics can be employed for these analyses easily. The average relative error realized through this method is less than 18%.

This paper presents the problem of controlling multiple tasks in a prioritized scheme during accidental external physical interaction with redundant robot. This issue arises when robots are employed in social, unknown, dynamic environments for complex and critical missions. Exploiting robot redundancy to ensure safety and compliance during performing hierarchical tasks is considered in this work. A general approach to control the main task (position/orientation of the end-effector) with allocated priorities beside compliance behavior in the null space of the tasks is proposed. External interactions on the robot body are estimated with an appropriate observer without using any force/torque sensors which is further used to bring compliance in the redundant space. A novel task allocation method is proposed and the convergence of the task space error, interaction estimation error as well as null space velocities are guaranteed. Finally, the performance of the method is investigated through computer simulation and real experiments on KUKA robot arm.

In order to study the temporal and spatial distribution of drought in Hamadan province, statistics of eleven of province stations for a period of 27 years was used, and after performing validation and homogeneity tests, it was normalized with drought by the Gibbs and Mohr method, and SPI index for years of drought occurrence in the province was determined. According to this, in the years 1996 and 1999 the most severe drought has occurred. After the dry years were determined based on the Gibbs and Mohr method, the related maps were drawn up to determine its dispersion across the province, and finally, using the ranking of these indices, the final map was drawn according to which the intensity of droughts decreases from east to west, namely, the eastern and central regions have been more susceptible to drought in comparison with other parts of the province.