This paper involves the investigation of the FORWARD KINEMATIC problem of three 4-DOF parallel robots, named as 4-PRUR1, 4-PRUR2, 4-PUU, performing 3 translations and one rotation, namely Schonflies motion. The foregoing parallel robots are special cases of 3 parallel robots, named as 4-PR′R′R″R″, 4-PR″R″R′R′ and 4-PR″R′R′R″, respectively, arisen from the type synthesis performed for 4-DOF parallel mechanisms with identical KINEMATIC limb structures. Each robot has 4 identical KINEMATIC chains and each chain consists of one prismatic active joint and 4 revolute passive joints. Due to different direction of revolute joints in each limb, 3 different architectures are considered in this paper. The FORWARD KINEMATIC problem is explored in seven-dimensional KINEMATIC space using the so-called Study’s parameters and LIA algorithm and eventually, it has been shown that an algebraic expression of degree 4 indicates the FORWARD KINEMATIC of each KINEMATIC chains of parallel robots under study in this paper. Moreover, using homotopy continuation and comparison with resultant method, it reveals that the FORWARD KINEMATIC problem of this robots have up to 236,236 and 2 real solutions, respectively.

In this paper, the FORWARD KINEMATIC of the special cases of 4- R" R' R' R" R", 4- R" R" R" R' R' and 4- R" R" R' R' R" parallel mechanisms that respectively lead to two 4- R R U R with different geometric structures and one 4- R U U spatial 4-DOF parallel robots has been studied. They are originated from the type synthesis of 4-DOF parallel mechanisms with motion patterns of 3 T1R. Each of them is composed of four KINEMATIC chains and each chain consists of five revolute joints. The directions of revolute joints have been different with each others that create three different geometrical structures. The FORWARD KINEMATIC problem is done in three dimensional Euclidean space and finally, a univariate mathematical expression of degree 344, 462 and 8 is indicated the FORWARD KINEMATIC problem of each parallel robot. Also, the results are compared with simulations.

In this study, feedback linearization (FL) for 6R manipulator is designed, simulated and implemented. The presented input-output FL controller has achieved the desired performance for the complicated nonlinear terms in the arm‟s dynamic equations. Simulations were used to test the performance of the controller for point-to-point motion as well as continuous trajectory. The results of the point-to-point motion simulations and experiments were compared, where it indicates that the proposed approach preserved smooth motion in a very short process time with good accuracy. The dynamic load carrying capacity (DLCC), which is a criterion to determine FL controller performance on 6R robot, is also investigated, based on saturated torque of the motors and allowable error bounds. Moreover, it was shown that the control law is able to accurately represent closed-loop equations and simultaneously imposed desirable behavior on 6R robot.

In this paper, a new type of spherical has been fabricated by involute axes in the form of conical gears that can create an unlimited revolution for wrist without singularity. This wrist has the special ability due to its structure and mechanism to use robots for high precision applications and continuous movements without singularity. According to the drawings, the manufacturing of the model for molding and casting of pieces is carried out and then by machining, the dimensions of the parts are achieved to the standard of drawing. After the assembly, the mechanical work pieces are prepared. The direct and inverse KINEMATICs of the involute angles are obtained for the directions of the wrist. Also, according to the KINEMATICs of the robot, the position of the end-effector is calculated. At first, Matlab software is used to simulate the wrist model and also the experimental test is done for validation. At the end, the PD controller is designed to control the yaw, roll and pitch angles and the changes necessary to improve the wrist control have been applied in the controller and AVR-based microcontrollers. Finally, simulation results are verified through theoretical and experimental test.

Introduction It is common to use rod weeders for onion harvesting according to their prevention of root blocking in front of the machine and separation of onion bulbs from soil by shaking. Chesson et al., (1977), used a rod weeder for manufacturing an onion harvester. This machine had a rectangular rotor axis with 25mm×25mm cross section. The rotor power was provided by a hydro-motor. An investigation into onion losses during the harvesting operation showed that the majority of crop damages have been occurred due to the collision of rods with onion bulbs. Therefore, the objective of this study is to design and evaluate an onion harvester based on rod weeders with the capability of crop harvesting with minimum damage. Material and Methods The main components of the examined onion harvester are chassis, furrower, and power transmission system and excrescence axes. Rectangular 100mm×100mm and 40mm×80mm profiles with 4mm profile thickness are used to fabricate the chassis. The furrowers were installed on each side of the chassis as the first parts of the harvester that comes into contact with the soil. Power transmission system provided rotation of two axes from both sides of the machine due to the lack of space for working of two chains on the one side. Therefore, a gearbox having one input shaft and two output shafts was selected for the machine. The gearbox output shafts turn the rotors with a reduction ratio of 1 to 3. 5. The rotary motion of the excrescence axes cuts and moves the soil located under the onions bulbs upward and finally the onion bulbs are placed on the soil surface. Therefore, excrescence axes can be considered as the main part of the onion harvester. The excrescence shape of the axes were created by star wheels. Star wheels had a hole with a square section in center (30mm×30mm), for installing them on their shaft. Choosing this kind of the connection, dose not let star wheels to move freely. Also to limit the lateral movement of the star wheels on axis, metallic spacers were used between the adjacent pairs of them. To evaluate the machine performance three variable factors were defined: working depth (20 and 26 cm), FORWARD speed (3, 4. 5 and 6 Km h-1) and rotational speed of the excrescence axes (150, 220 and 290 rpm). The conducted experiments were analyzed in a complete randomized design with three replications. Results and Discussion The analysis of variance showed that the working depth and FORWARD velocity of axis had significant effect (in 5% level) on the success rate of onion harvester. Also the interaction between depth and FORWARD velocity and the interaction between rotational speed of axes and FORWARD speed were significant. The interaction between depth and rotational speed of axes and the interaction between depth, rotational speed of axes and FORWARD speed were not significant. Evaluation of the interaction between depth and FORWARD velocity showed that the most success rate of onion harvesting was in 20 cm depth and FORWARD velocity equal to 3 and 4. 5 km h-1. The least success was gained in 26 cm depth with 4. 5 and 6 km h-1 FORWARD speed. Evaluation of the interaction between rotational speed of axes and FORWARD speed showed that the most success in the onion harvesting was occurred with a machine having 3 km h-1 FORWARD velocity and 150 rpm rotational speed and also 4. 5 km h-1 FORWARD velocity and 220 rpm rotational speed. Conclusions The success rate of the onion harvesting decreased by increasing the working depth of the machine and axes distance to the onion bulbs. Also with excessive FORWARD velocity the success rate of onion harvesting decreased because of difficulties in controlling the tractor guidance in straight line. The best performance of this onion harvesting machine was in 20 cm depth, 4. 5 km h-1 FORWARD velocity and 220 rpm axes rotational speed. Adjusting the machine working parameters according to these values, the ratio of the linear speed of the star wheel tips to the FORWARD velocity of the machine (KINEMATIC index) was equal to 0. 82.

This paper offers a modified circuit for improving linearization of power amplifier with based on the model of the Feed FORWARD circuit amplifier. With the help of mathematical model for the single power amplifier, the circuit is simulated und a demonstrator is built and measured. it is used a complex Taylor series for modeling the power amplifier by the approximation of the amplitude transfer function and the level-dependence of the transmission-phase of the power amplifier and can be understood as a simplified form of Volterra series. In our proof of concept experiment, we verified the concept but also found that the adjustment of the circuit is critically dependent on the drive conditions and linearization is achieved only for a narrow range of drive power. The simulation of the total circuit is largely determined by the models for the transmission characteristics of the two power amplifiers. The new circuit in compare with the conventional Feed FORWARD amplifier, in addition a significant increase in efficiency to minimize the power of the distortion signal 3IMD for large driving amplitude (large signals).