Parallel robots exhibit superior precision to serial robots. They operate with reduced power consumption due to load distribution among individual motors. However, symmetrical parallel robots employing a 1T2R structure encounter challenges with parasitic movements at the end-effector, leading to control complexities and application limitations. This study aimed to downsize the robot while ensuring its operational range by employing origami techniques. Addressing the inherent weakness of origami’s stiffness, various methods of material stacking and designed joints with diverse materials and thicknesses were proposed to meet specific angle requirements for each component. The developed control model was validated through simulations and experiments, effectively minimizing parasitic movements by verifying the robot"s motion.

The objective of this study was to present a rotary manipulating system driven by a rotary actuator based on twisted shape memory alloy (SMA) wires. The rotary actuator was composed of two oppositely twisted SMA wires connecting a rotor and a stator through a shaft. Two oppositely twisted SMA wires could generate bidirectional rotary motions upon actuation of each twisted SMA wire corresponding to the direction against the twist direction of each SMA wire. A manipulator was designed and fabricated by integrating manipulating arms, the rotary actuator, and a Hall effect magnetic rotary encoder which could measure the angular position of the rotary motion. We modeled and characterized the manipulator upon application of a ramp current input to each twisted SMA wire. A proportional-integral-derivative (PID) controller was designed and implemented to control the proposed rotary manipulator. Reference angular position tracking performances of the manipulator were evaluated with a series of experiments.

This paper presents a distortion compensation algorithm for cable-driven master devices. Such device has four string pots at four corners of a frame. Four cables are tied from the four corners to the center holder. When the central holder, which is a haptic grip, moves, lengths of the four cables will change. From the four cable lengths, the spatial position of the haptic grip can be estimated using triangulation. In this case, distortion such as barrel image of the image field occurs when estimating a position with an offset parallel to the plane in which the four string pots are located. The closer to the corner, the smaller the position estimate value is than the true value. After distortion phenomenon is modeled by projecting onto the ellipsoid, the position in the vertical direction of the cable plane is compensated by the corresponding value and flattened. The mean error in the x-direction position was improved by 91% from 0.7833±0.8381 mm to -0.0709±0.4341 mm. This cable-driven master device can be used as a haptic device for operating a surgical robot.

Industrial robot manipulators require high absolute position accuracy of the end effector to perform precise and complex tasks. However, manufacturing errors cause differences between nominal and actual parameters, and errors between the expected and actual positions of the end effector, resulting in undesired lower absolute position accuracy. Accordingly, to increase the absolute position accuracy of the end effector, kinematic calibration is required to correct the nominal parameters close to the actual parameters. However, in this study, redundancy of parameters may occur from the overlapping degrees of freedom of parameters in adjacent frames, which causes the problem of unnecessarily correcting many parameters in the optimization process. Thus, to solve this problem and use only the necessary parameters, this paper focuses on the linear relationship of redundant parameters and proposes a method of automatically discriminating and removing it through the Pearson Correlation Analysis. Additionally, through simulations on the two manipulator models, we verify the accuracy of redundancy of parameters determined by the proposed method, and demonstrate consistency and efficiency by comparing the results before and after redundancy removal.

Tool-center-point (TCP) calibration and geometric error identification procedures are proposed to improve the accuracy of a 6-axis manipulator with a tilting rotary table. The accuracy of a 6-axis manipulator is affected by the accuracy of TCP calibration. In general, TCP calibration of the 6-axis manipulator uses a conical fixture provided by the manufacturer. However, since a TCP cannot be accurately positioned to the tip of the conical fixture repeatedly, a large positional deviation occurs at the calibration depending on the worker proficiency. Thus, accuracies of TCP calibration and the 6-axis manipulator are reduced. In this paper, a 3-DOF measuring device, consisting of a nest with three dial gauges and a precision ball, is developed to calibrate the TCP and to improve the accuracy of the 6-axis manipulator. Then, geometric errors of a tilting rotary table are identified via double ball-bar measurements according to the ISO 10791-6 with TCP initial alignment using an extension fixture. Finally, proposed TCP calibration and geometric error identification procedures are validated experimentally, and they show improvements in positional accuracy by 55 and 90%, respectively.

In this study, we developed a hydraulic manipulator to assist firefighters and rescue personnel at disaster sites. In the design procedure, we analyzed the manipulator considering the hydraulic actuators as well as the manipulator kinematics and dynamics. For the user interface, a macro/manual operation concept was proposed to provide an effective response in emergency and disaster situations. To cope with abnormalities of the disaster site operator, a protocol for switching local/remote operations was developed. The effectiveness of the hydraulic manipulator and operating system was verified through task implementation experiment.

In this paper, we designed and manufactured a new manipulator (less than 15 kg) to make the total weight of SCOBOT-200 (EOD robot: its platform weight is 35 kg) commercialized by FIRSTEC Co., Ltd. Link1 and Link2 of the manipulator were designed and fabricated using CFRP (Carbon Fiber Reinforced Plastics) material, and the other components were made of AL6061 material. The fabricated manipulator has 5-DOF, and the opening width of the gripper is more than 1520 mm. As a result of the characteristic test, the weight of manipulator is 14.5 kg, the length of the manipulator is 1500 mm, the payload when the manipulator extended is 8 kg, when folded is 20 kg. Thus, the manipulator manufactured can be used as a manipulator for a small EOD (Explosive Ordnance Disposal) robot.

This paper presents a finite-time tracking control for a robot manipulator in the presence of a modeling uncertainty and an external disturbance. To solve the large chattering phenomenon that is caused by the high switching gain of the slidingmode control, a novel second-order sliding-mode controller that generates a continuous control input is designed with a robust differentiator. The finite-time stability of the closed-loop system is ensured using a constructive Lyapunov-stability analysis. Finally, a numerical simulation of the 2-Axis Pan-Tilt system is performed to verify the effectiveness of the proposed controller.