Direct-drive SCARA Robot Research Articles

Dynamic Modeling, Simulation, and Experimental Verification of a Wafer Handling SCARA Robot With Decoupling Servo Control

In this paper, we propose a novel coordinated control method based on decoupling servo control to design a 4-DOF direct-drive SCARA robot for wafer handling purpose. As the basis of decoupling servo control, the dynamic model of the SCARA robot is obtained with two methods, the Newton-Euler equation, and Lagrangian equation. The validity of this SCARA dynamic equation is confirmed by these two methods. Due to disturbance and model uncertainty, three PD plus robust controllers are individually applied to three axes of the SCARA robot, together with decoupling control on three physically dynamically highly coupled robotic arms. The inverse dynamics of the SCARA robot is analyzed by feedback linearization, and the experimental results show that above PD plus robust controllers and decoupling control reduce the position tracking error effectively. Performance meets with the high speed and high precision requirements in the wafer handling process. The experimental data shows that the decoupling control algorithm makes the SCARA robot performance improved a lot. The position errors during dynamic tracking movement and the static errors are reduced by 4 to 20 times.

Fuzzy Control Algorithm Eliminating Steady-state Position Errors of Robotic Manipulators

In order to eliminate position errors existing at the steady state in the motion control of robotic manipulators, a new fuzzy control algorithm is propeosed using three variables, position error, velocity error and integral of position errors as input variables of the fuzzy controller. Although the number of input variables of the fuzzy controller is increased from two to three, the number of fuzzy control rules is just increased by two. Three dimensional look-up table is used to reduce the computational time in real-time control, and a technique reducing the amount of necessary memory is introduced. Simulation and experimental studies show that the position errors at the steady state are decreased more than 90% compared to those of existing fuzzy controller when the proposed fuzzy controller is applied to the 2 axis direct drive SCARA robot manipulator.

Experimental Evaluation of Feedforward Control Based on the Dynamic Models of A Direct Drive SCARA Robot

A SCARA type direct drive robot which can be used in the assembly operation was designed and manufactured. Graphite fiber epoxy composite material was used in the fabrication of the robot arm structure in order to improve the speed of the robot arm with a high damping effect. For model-based control and sensitivity analysis of system parameters, the dynamic model of robot arm and drive servo amplifier parameters such as equivalent gains of PWM driver and velocity gains of servo system were estimated from frequency response tests. The complete dynamic model for overall robot system was used in the simulation of the open-loop control. The simulation results agreed reasonably well to the experimental results. The feedforward control using the dynamic models improved the trajectory tracking performance, decreasing the tracking error by factor of three compared with PID control. This study found that the inverse dynamic model of the robot arm including the drive servo system showed better performances than the case of arm dynamic model only.

A comparison of model-based path control algorithms for direct-drive SCARA robots

Various advanced control strategies are applied to a direct-drive SCARA robot and studied in computer simulations. Besides computed torque control and direct adaptive control, heuristic optimal control, a new path control scheme for robotic manipulators, is included in the comparison study. PD control, the traditional robot control method, is used for generating a comparing baseline. While all schemes are applied for the same tracking task, the effect of modelling errors and measurement noise is considered in robot performance evaluation. Simulation results show that (1) without model errors, all advanced control schemes can achieve higher tracking accuracy than PD control; (2) with a random measurement error of 1%, computed torque and direct adaptive control methods are inferior to PD control; (3) heuristic control proves to be the most robust control scheme in case of mixed model and measurement errors.

An adaptive controller for a direct-drive SCARA robot

A direct adaptive controller for trajectory tracking of high-speed robots such as a direct-drive SCARA robot is presented. In this robot, nonlinear effects due to centrifugal, Coriolis, and inertial forces are more important than friction and gravity forces, unlike most industrial robots. The control law of the adaptive scheme consists of a PD regulator plus feedforward compensation of full dynamics. The feedforward terms are adjusted by an adaptation law so that the steady-state position errors are zero. With this adaptive controller, the joint acceleration measurement is not required and no inversion of the estimated mass matrix is involved. The tracking performances of the controller applied to a two-degree-of-freedom SCARA is illustrated by a real-time implementation based on a single-chip digital signal processor (DSP). >