• Journal of Institute of Control, Robotics and Systems
• /
• v.22 no.11
• /
• pp.960-966
• /
• 2016

This paper proposes a new concept of a soft and wearable upper-limb exoskeleton. A novel actuation principle, called the twisted string actuation principle, is implemented to make it lightweight, soft, and therefore easily wearable. Its power transmission mechanism and harness are designed to be soft and wearable, yet have enough control accuracy for rehabilitation. In addition to force transmission optimization, a speed enlargement mechanism is newly introduced in order to increase the contraction speed of the twisted string actuation mechanism by sacrificing the unnecessarily large gear reduction ratio of the twisted string mechanism. A prototype has been tested for mirroring therapy, and the feasibility of the proposed mechanism has been shown through a sufficiently accurate tracking performance.

• Journal of Industrial Technology
• /
• v.19
• /
• pp.321-329
• /
• 1999

An automated manufacturing process mechanism for string musical instruments has been designed in this study. In contrast to other manufacturing products, classical string instruments try to preserve their traditional design shapes even in these days and involve variety of wood working(carpentry) characteristics including highly skilled curved surfaces treatments. Great efforts have been put to develop an integrated and automated system for improved product quality and process control, reduced physical labors, better safety etc. They, however, have been limited to devise jigs and tools with regard to selected processes due to lack of technology and research man-powers. We carefully examined the products and process characteristics, and an automated mechanism which overcome prevailing drawbacks has been derived.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.26 no.3
• /
• pp.196-201
• /
• 2016

This paper analyses the characteristics of a stiffness-based rehabilitation mechanism for improving the function of the elbow joint of a human. We consider an elastic string as a tool for the elbow joint rehabilitation, where the string has been modeled as a linear spring with a stiffness. For effective rehabilitation training by using such a mechanism, we need to analyse the available torque characteristics of the elbow joint according to the stiffness of the string. Through various simulations, the torque pattern and its range of the elbow joint by assigning the stiffness of the string have been identified for a pre-defined trajectory of motion of the elbow joint. Finally, we show that the specified stiffness-based rehabilitation scheme can be used for effective rehabilitation of the elbow joint.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.4
• /
• pp.289-296
• /
• 2017

In this paper, geometrical optimization for newly designed flapping mechanism for insect-like micro air vehicle is presented. The mechanism uses strings to convert rotation of motor to reciprocating wing motion to reduce the total weight and inertial force. The governing algorithm of movement of the mechanism is established considering the characteristic of string that only tensile force can be acted by string, to optimize the kinematics. Modified pattern search method which is complemented to avoid converging into local optimum is adopted to the geometrical optimization of the mechanism. Then, prototype of the optimized geometry is produced and experimented to check the feasibility of the mechanism and the optimization method. The results from optimization and experiment shows good agreement in flapping amplitude and other wing kinematics. Further research will be conducted on dynamic analysis of the mechanism and detailed specification of the prototype.

• The Journal of Korea Robotics Society
• /
• v.19 no.3
• /
• pp.244-253
• /
• 2024

This paper presents a novel stem-cutting device using a twisted string actuation system combined with the cinch bag-typed gripper proposed in previous research. The suggested cutting device was developed to cut the stem of a tomato using two motors. The relationship between contact time and motor angle was mathematically induced, and the contacting time was verified through the experiments. The contact time has decreased as the offset of each pair of strings at the disk increases. The contact time and its deviation were reduced by increasing the radius of the twisted string bundle, and the motor torque to exert an equivalent cutting force was surged at the same time. The proposed cutting mechanism with 16 strands of twisted string bundle and 40 mm of offset can cut the given tomato stems and stalks, exerting up to 132.4 N of cutting force in 4.6 to 6.5seconds.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.10a
• /
• pp.9-10
• /
• 2006

• The Journal of Korea Robotics Society
• /
• v.14 no.3
• /
• pp.221-227
• /
• 2019

This paper studies an effect of vibration on twisted string actuation inside conduit at high curvature angles. In our previous work. we have mentioned that twisted string actuators can be used to transmit power even at significant curvature angles of the conduit. However, several undesirable effects, namely pull-back, hysteresis, and chattering, were present during actuation due to friction between strings and the internal sheath of the conduit. This paper reports the results of experimental study on effects of vibration on twisted string actuation inside curved conduits. We have demonstrated that applying vibration generated near natural frequency of the system during the stages of twisting and untwisting cycles helped reduce pull-back and hysteresis and increase string contraction. In case when sheath was deflected by $180^{\circ}$ under a constant load of 3 kg, we were able to achieve over 40% decrease in pull-back and 30% decrease in hysteresis, compared with no vibration case.

• Journal of Institute of Control, Robotics and Systems
• /
• v.21 no.6
• /
• pp.524-530
• /
• 2015

Early wearable robotic devices were big, powerful and manipulator-like. Recently, various applications of wearable robotics have shown a greater demand for lower weight and compliancy. One approach to achieve these objectives is the use of novel actuators such as twisted string actuators. These actuator are very light, quiet, mechanically simple and compliant. Therefore, they can drastically decrease the weight and size of robotic systems such as exoskeletons. However, one drawback of this actuator is its nonlinear transmission ratio, which is established as a ratio between the angle of twisting of the strings and their resulting contraction. In this paper, we propose a transmission mechanism with rotational motion as the output incorporating a twisted string actuator (TSA). The designed mechanism allows the linearization of the relationships between the input and output displacements and forces of a TSA. The proposed design has been validated theoretically and through a set of computer simulations. A detailed analysis of the performance of the proposed mechanism is presented in this paper along with a design guideline.

• Journal of Korean Association for Spatial Structures
• /
• v.6 no.3 s.21
• /
• pp.111-121
• /
• 2006

Beam String Structure is a structure system that is composed with beam, strut and string, and the structural capacity of this structure system is enhanced by introducing prestress force in string and controling the stress and deformation of beam. Researching on the established studies and examples, character and composition methods of Beam String Structure was investigated. At the result, It was examined that the design elements of the system are shape and rise of beam, sag of string, plan arrangement and the composition and number of strut, in addition, detailed composition methods of the design elements were represented. Also, it was showed that the method to form the individual mechanism against additional load can be employed in order to reduce stress of Beam String Structure under the heavy additional load.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.7
• /
• pp.745-750
• /
• 2012

This study extends the constraint force design method allowing topology optimization for planar rigid-link and string mechanisms. To our best knowledge, by applying conventional machine and mechanism design theories, it is likely that it is possible to find out optimal locations of joints and lengths of rigid-links but somewhat difficult to find out optimal topology of rigid-links. To achieve optimal topology of rigid links, there is our previous contribution so called the new constraint force design method with the binary design variables determining the existence of the auxiliary forces imposing apparent lengths among unit masses. By adding new binary design variables, this research extends the constraint force design method to find out optimal mechanism consisting of stringy links as well as rigid links that seems impossible in the conventional machine and mechanism design theories.