Balanced Manipulators Research Articles

On the Internal Counter-Torque between Springs in Serially Connected Statically Balanced Manipulators

Serially connected statically balanced manipulators with springs have been used in many applications. However, a portion of the torques caused by springs countering each other lead to an imbalance in gravitational torques and, therefore, are deemed as waste torques for springs to achieve static balance. In this paper, the torque contribution of a typical spring is classified as gravity-balancing torque and counter-torque based on the accumulated joint angle of the gravitational torque. Then, the internal counter-torque is defined as the sum of the magnitude of the terms of these counter-torques at each joint. Through the adjustment of spring attachment parameters, the internal counter-torque can be minimized with preferable spring attachment parameters while maintaining a static-balancing condition. A typical four-link manipulator with a preselected spring configuration is shown as an illustrative example. The results show that there are 28% and 50% reductions in the internal counter-torque at joints 2 and 3, respectively, through the adjustment of spring attachment parameters. Hence, the waste torques in statically balanced serially connected manipulators are reduced to the lowest quantity.

Goals and Problems of Improving of Electromechanical Control System of SHBM-150M Type Balanced Manipulator

The movement of different objects in area is main part of most operations. Often that movements are performed by various types of balanced manipulators. The analysis of a Russian manipulator of ShBM-150M type was completed, the specifics design and applied sensorless vector control system of induction motor are considered. The disadvantageous of manipulator work due to the current control system are detected. The factors of low position precision of cargo at fixation on tags are determined. The elastic vibrations of the manipulator mechanical part, which adversely affect for its work quality, have been experimentally identified and researched. The design model of multi-mass mechanical system is presented. The improvement goals of the control system of ShBM-150M manipulator are defined for upgrade of technical parameters, ease of operation and functional capability.

On the Use of Electromechanical Systems for Limiting Dynamic Loads in Spring Mechanisms

Active methods for damping the oscillations and limiting the dynamic loads of spring machine elements that are implemented owing to the additional force effects created by an electric drive providing the reduction of maximum work in spring gears of operated machinery were studied. The main parameters and energy characteristics of electromechanical systems that affect the efficiency of using of active means of dynamic load limitation by an electric drive in spring elements of mechanical gears were determined. It was shown that the maximum value of electric-engine current and its rate of change can decrease the efficiency of the active dynamic load limitation in machines by an electric drive and impede its practical implementation. Analytic equations for calculating the minimax torque (current) values of an engine and EMF of its supplying converter required for an effective decrease of the dynamic loads in spring machine elements were derived. The effects of the hardware and electric-drive parameters on the efficiency of decreasing dynamic loads in spring mechanical gears was specified. Research was performed to determine the efficiency and range of application of the active methods of dynamic load limitation in spring gears of machines using the existing electric drives. The results of the research were used in the implementation of active means of dynamic load limitation by an electric drive in spring gears of the thrust mechanism of an EKG-4.6B mine excavator and the digging mechanisms of EKG-20 excavators, as well as for decreasing the speed and force oscillations of the operating parts of balanced MP-100 manipulators and the weightless environment of zero-gravity simulators for training astronauts.

Methods of Efficient Parameters Multifactorial Determination of Industrial Manipulators Gears and Electric Drives

The method of multifactorial determination of efficient parameters of springy gears and electric drives of load vertical traverse by the balanced manipulators is developed. The complex approach is offered in relation to the power circuit choice of the electromechanical force compensating systems taking into account minimization of mass, applicability of a nonreversible motor and work with low value of the maximum torques, active limitation of dynamic efforts in springy elements of mechanics using electric drive and other factors allowing to improve the design of electromechanical systems of special lifting devices, industrial manipulators and robots, simulator complexes and testing workbenches. The choice of the desired reduction radius value of the gear from the allowable value range is recommended to be made using two approaches: an optimum setting using minimization criterion of the total maximum motor torque and a compromise derivative of the efficient value of the reduction radius satisfying performance of all the considered conditions.

Conditions of optimization and efficiency of damping of oscillations of elastic mechanisms by an electric drive

Oscillations occurring in elastic structures and long mechanical transmissions of operating machines lead to an increase in regulation errors of the controlled coordinates and increase in the dynamic loads in electromechanical systems with elastic connections (EMSs with ECs), which decreases the quality of the manufactured products and reliability and long-term operation of the mechanisms and leads to significant economic damage. Determination of the limit capabilities of the electric drive (ED) while damping the oscillations of elastic mechanisms is of practical interest. A mathematical model of the electromechanical systems with elastic connections in the form of a Mason directed graph is considered. The main factors influencing the efficiency of damping of the electric oscillations of operating machines’ mechanical transmission by the ED are defined. The conditions of optimization and reasonable parameters of regulators of the slave regulation system (SRS) providing the smallest amplitude of the oscillations of the elastic mechanisms by the electric drive are found. The efficiency of the suggested recommendations on implementation of regulators of electromechanical systems with elastic connections has been confirmed in practice during modernization of an AT-500-230-1 roller electric drive processing plastic materials and balanced manipulators of MP-100 type. It is shown that the efficiency of damping the oscillations on the elastic mechanical transmissions of operating machines by the electric drove depends on the structure and parameters of the regulators of the slave regulation systems, the rational values of which should be determined taking into account the resonance frequency of an EMS with an EC. Settings are proposed of slave regulation systems permitted providing the minimum possible amplitude of oscillations of the torque in the elastic transmissions of the mechanisms caused by the change of the disturbing action.

Trajectory control of mass balanced manipulators

Trajectory tracing of the manipulator tip in work space is one of the important research areas. Accurately controlling robot movement along a predetermined trajectory is necessary for many applications like arc welding and laser cutting. Several methods are developed for this purpose. In this study robot arms are first reduced into dynamically equivalent point masses and balanced to eliminate gravity terms from the dynamical equations and also decouple them. Simple PD control is used at each servomotor for position control. Positional and velocity feedback gain factors are computed for a second-order critically damped linear control model. Satisfactory results are obtained for tracing straight line trajectory defined in the work space of the manipulator.

Dynamic Characteristics of Balanced Robotic Manipulators with Joint Flexibility

SUMMARYThe mass balancing of robotic manipulators has been shown to have favorable effects on the dynamic characteristics. In actual practice, however, since conventional manipulators have flexibility at their joints, the improved dynamic properties obtainable for rigid manipulators may be influenced by those joint flexibilities. This paper investigates the effects of the joint flexibility on the dynamic properties and the controlled performance of a balanced robotic manipulator. The natural frequency distribution and damping characteristics were investigated through frequency response analyses. To evaluate the dynamic performance a series of simulation studies of the open loop dynamics were made for various trajectories, operating velocities, and joint stiffnesses. These simulations were also carried out for the balanced manipulator with a PD controller built-in inside motor control loop. The results show that, at low speed, the joint flexibility nearly does not influence the performance of the balanced manipulator, but at high speed it tends to render the balanced manipulator susceptible to vibratory motion and yields large joint deformation error.

Dynamic characteristics of balanced robotic manipulators with joints flexibility

SummaryThe mass balancing of robotic manipulators has been shown to have favorable effects on their dynamic characteristics. In actual practice, however, since conventional manipulators have flexibility at their joints, the improved dynamic properties obtainable for rigid manipulators may be influenced by those joints flexibilities. This paper investigates the effects of the joints flexibility on the dynamic properties and the controlled performance of a balanced robotic manipulator. The natural frequency distribution and damping characteristics were investigated through frequency response analyses. To evaluate the dynamic performance a series of simulation studies of the open-loop dynamics were made for various trajectories, operating velocities, and joint stiffnesses. These simulations were also carried out for the balanced manipulator with a PD controller situated inside the motor control loop. The results show that, at low speed, the joints flexibility does but little influence the performance of the balanced manipulator, but at high speed it tends to render the balanced manipulator susceptible to vibratory motion and yields large joints deformation errors.

Neural network-based control of balanced robotic manipulators with joint flexibility

This paper addresses an improvement on the controlled performance of balanced manipulators in a practical level by implementing neural network based controller. The mass balancing of robotic manipulators has been shown to have favorable effects on the dynamic characteristics. However, it was also pointed out that for the manipulators having a certain degree of flexibility at the joints, due to the lowered structural natural frequencies and reduced velocity related terms, mass balancing results in vibratory motion at high speed operation. Such a vibratory tendency of the balanced flexible joint manipulator limits the admissible range of servo gains of the conventional controllers, making those controllers unsuitable for controlling the manipulator at high speeds. To avoid such difficulty, an artificial neural network (NN) controller is introduced to realize the dynamic control of the balanced flexible joint manipulators. A feedforward type of NN controller is proposed and its performance is evaluated through a series of numerical simulations. The proposed NN controller showed much better tracking performances over the conventional PD controller.

Time Optimal Control of Balanced Manipulators

An efficient algorithm is presented for solving time-optimal control for a restricted class of manipulators: balanced, decoupled manipulators. It is shown how the dynamics of such manipulators are sufficiently simple that optimal control solutions for point-to-point moves can be found analytically. A change of coordinates is proposed in which the more difficult problem of time-optimal interception of moving targets can be solved efficiently. A fast algorithm is described for computing and updating optimal interception solutions on line.

Sensitivity analysis of balanced robotic manipulators

SUMMARYThe payload variation has been one of the principal reasons in reducing path tracking accuracy and complicating controller design. In this paper, the trajectory and input sensitivities for the payload variation are investigated for three different robot configurations which include unbalanced, inaccurately balanced and balanced configurations. Based upon the sensitivity theory, simulation studies were made to evaluate the sensitivities of these configurations with respect to payload variations. The simulation results are discussed in detail and compared for the three configurations.