This paper presents the design, stability analysis and experimental validation of a computationally non-intensive, model-free, intelligent proportional-integral (iPI) controller for flexible joint manipulators. In order to show the performance of the iPI controller, it is compared with classical proportional-integral and proportional-integral-derivative controllers. Based on this comparison, the iPI-controlled system achieved a better than 60% tracking accuracy for both kane trajectory and sine input tracking. The iPI controller also significantly reduced transient swings in the flexible joint of the manipulator, when tracking a train of pulses. Moreover, the iPI controlled system successfully eliminated both disturbances and noise effects from the dynamics of the manipulator.

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This paper presents the design and control of a single-link flexible-joint robot manipulator. A cascade fuzzy logic controller (FLC) was used to remove link vibrations and to obtain fast trajectory tracking performance.The cascade FLC structure includes 3 different FLCs. The input variables of the first and the second FLCs are the motor rotation angle error, its derivative, and the end-point deflection error its derivative, respectively. The outputs of these controllers are the inputs of the third FLC, which yields the control signal to the flexible robot arm. All of the FLCs were embedded in a DS1103 real-time control board. Several experiments were conducted to verify the controller performance. In the step-response experiments, the error of motor rotation angle was obtained as less than 0.12 • and there was no steady-state error in the end-point deflection. In trajectory tracking experiments with the same FLC structure, small errors and phase shifts in the system variables occurred. Model parameters of the flexible arm such as link length and spring stiffness were changed to test the robustness of the FLC. It was seen that the FLCs were very robust to internal and external disturbances. Considering the results of the experiments, the proposed FLC structure shows efficient control performance in flexible robot arms.

This paper presents the development, stability analysis and validation of an intelligent proportional integral (iPI) controller for the tip position control of a flexible-link manipulator. A stability analysis included in the paper shows that the iPI controller is equivalent to the proportional integral-squared controller. In order to verify the performance of the iPI controller, several experiments were conducted. In these experiments, step and square-wave inputs and two other trajectories were applied to the flexible-link manipulator. Also, the performance of the iPI controller was compared with those of classical PI and PID controllers. The results obtained from the comparison experiments showed that, the PI and PID controllers produced better performance in step and square-wave inputs, but the iPI controller yielded better trajectory tracking performance. All of the controllers were tested for disturbance and noise rejection capability. The iPI controller eliminated disturbance and noise better than the classical controllers. Considering all of the results, the iPI controller has great potential in trajectory tracking control of flexible-link manipulators.

This paper presents a new control scheme for a flexible-joint manipulator using a higher-order differential feedback controller (HODFC). Two higher-order differential operators were designed and used to perform observations of both the reference input and the output of the manipulator, together with the requisite state derivatives. An error-based state-space model was then derived from the observed states. A pole-placement procedure with filtering was then used to drive the system error to zero. Practical controller implementation was carried out using the dSPACE real-time prototyping system. For the comparative validation of the performance of the HODFC with respect to a classical proportional-integral and proportional-integral-derivative (PID) controller, several experiments were undertaken. In these experiments, the step input, sine waves, kane trajectories, and external disturbances were applied to the controlled flexible-joint manipulator. The results showed that the HODFC controller eliminated disturbances within one second of occurrence, and produced superior kane trajectory tracking. Moreover, based on the root-mean-square tracking error criterion, the HODFC was observed to track both the sine and kane function trajectories with one-fourth the tracking error obtained with classical PID control.

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The trajectory tracking in the flexible-joint manipulator (FJM) system becomes complicated since the flexibility of the joint of the FJM superimposes vibrations and nonminimum phase characteristics. In this paper, a distributed higher-order differential feedback controller (DHODFC) using the link and joint position measurement was developed to reduce joint vibration in step input response and to improve tracking behavior in reference trajectory tracking control. In contrast to the classical higher-order differential (HOD), the dynamics of the joint and link are considered separately in DHODFC. In order to validate the performance of the DHODFC, step input, trajectory tracking, and disturbance rejection experiments are conducted. In order to illustrate the differences between classical HOD and DHODFC, the performance of these controllers is compared based on tracking errors and energy of control signal in the tracking experiments and fundamental dynamic characteristics in the step response experiments. DHODFC produces better tracking errors with almost same control effort in the reference tracking experiments and a faster settling time, less or no overshoot, and higher robustness in the step input experiments. Dynamic behavior of DHODFC is examined in continuous and discontinues inputs. The experimental results showed that the DHODFC is successful in the elimination of the nonminimum phase dynamics, reducing overshoots in the tracking of such discontinuous input trajectories as step and square waveforms and the rapid damping of joint vibrations.