텐던 기반 직렬 기구의 외부 중력 보상 장치 설계

이기현(Gihyeon Lee),김진현(Jinhyun Kim) 제어로봇시스템학회 2020 제어·로봇·시스템학회 논문지 Vol.26 No.5

In this paper, the external gravitational compensation device of a tendon-based serial instrument was studied. Typically, a spring-based gravitational compensation device produces a compensation force that is in proportion to the angle of the link to which it wishes to perform the gravitational compensation. However, if several links are connected in a series, it is difficult to generate adequate compensation forces on all links because the orientation of gravity varies depending on the angle of the previous link, thereby rendering the necessary compensation forces variable. Therefore, in the case of a multi-axis serial mechanism, a gravitational compensation device using a parallelogram mechanism capable of transmitting a reference plane with respect to the direction of gravity has been widely used. A serial mechanism using a parallelogram mechanism for the gravitational compensation device is advantageous because gravitational compensation is possible by transmitting the reference plane to all links in the direction of gravity, regardless of the angle of each link. The only disadvantage is that it is difficult to manufacture due to its small size. To compensate for these drawbacks, we propose an external gravitational compensation device that is applicable to tendon-based series mechanisms. The proposed external gravitational compensation device can mediate reference plane transfer and gravitational compensation through tendons outside the serial mechanism, and it is advantageous in that the size and weight of the link can be reduced because it is installed outside the link. In this paper, we designed and verified the reference plane control mechanism that could transfer the reference plane similar to the parallelogram mechanism from the outside and the gravitational compensation mechanism that could mediate gravitational compensation according to the angle of each link. In addition, the prototype was assembled and experimentally verified.

Static balancer for the neck of a face robot

Cho, Changhyun,Kim, Seungjong SAGE Publications 2014 Proceedings of the Institution of Mechanical Engin Vol.228 No.3

<P>We propose a 3-degree of freedom gravity compensator for the neck of a robotic face. The neck of the face robot is configured with yaw-pitch-pitch-roll rotations. Since the yaw rotation is made parallel to gravity, only the pitch-pitch-roll rotations are considered for gravity compensation. The 1-degree of freedom gravity compensator is located at the first pitch joint. A 2-degree of freedom gravity compensator equivalent to the existing gravity compensator is proposed and applied to the second pitch and roll rotations. A parallelogram is adopted between the first and second pitch rotations. One end of the 2-degree of freedom gravity compensator is attached at the parallelogram and the other is fixed at the face. Wires are used to realize a zero-length spring for all gravity compensators and all springs are located at the base for compact design. Experimental results for gravity compensation show that gravitational torques were effectively counterbalanced by the proposed 3-degree of freedom gravity compensator.</P>

중력 보상 기구 오차의 원인과 스프링 무게 중심 변화

서경준,서정욱 제어로봇시스템학회 2021 제어로봇시스템학회 국내학술대회 논문집 Vol.2021 No.6

Gravity compensation mechanism is one of the oldest topics in robotics. Mechanical gravity compensation can theoretically make the motor unloaded. Compensation torque generated by spring tension removes the torque caused by gravity. However, when tensile or compressive force is applied to the spring, the gravity center of the overall rotating linkage changes. It can even cause the overall compensation torque error. Specific research is needed that the center of gravity change causes errors in the overall torque. In the paper, assuming there is no friction and zero idler radius, the error torque due to the change of the gravity center of the overall rotating linkage is calculated. This research proposes a method to identify the overall cause of gravitational center change error caused by moving back and forth of the spring. Studying mechanisms for reducing gravity errors to improve performance will also help to design a multiple degree of freedom manipulator.

Robotic Manipulators Employing a Bevel Gravity Compensator

조창현,강성철,이우섭 제어·로봇·시스템학회 2012 International Journal of Control, Automation, and Vol.10 No.2

This paper presents robotic manipulators that employ the bevel gravity compensator. The bevel gravity compensator can counterbalance a 2-dof rotation comprised of two 1-dof gravity com-pensators and a bevel differential. Each 1-dof gravity compensator is equipped at the rotating bevel gear, respectively. Analyses of the energy and torque for a 1-link and 2-dof manipulator indicate that the proposed gravity compensator performs static balancing completely. Multi-link and spatial manipulator applications are discussed in this paper. In these applications, mechanical constraints are adopted to achieve complete gravity compensation, since the pose of the distal link with respect to the inertial frame varies with alterations of the pose of the proximal link. Energy analyses reveal that the proposed manipulators employing bevel gravity compensators can completely achieve static balancing. The simulation results show that the gravitational torques can be effectively counterbalanced in regards to the proposed manipulators.

Incomplete gravity compensator for a 4-DOF manipulator

김상형,조창현 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.10

This paper proposes gravity compensators for a 4-degree-of-freedom (4-DOF) humanlike manipulator. Eighteen springs (or 1-DOFgravity compensators) are required to achieve complete static balancing of a 4-DOF manipulator. Because locating 18 springs is impractical,incomplete gravity compensators are designed for practical implementation in this paper. Springs are selected using an objectivefunction of the gravity compensation and design cost. The design cost indicates the complexity of the mechanisms. As a result, four- andtwo-spring designs are obtained. Optimizations of spring constants of the four- and two-spring designs are conducted for the objectivefunction of gravity compensation. The torque ratios for the four-spring design are computed as [18.64%, 11.92%, 77.68%, 81.14%]. Thetorque ratios for the two-spring design are computed as [16.03%, 20.22%, 100.00%, 100.00%] and indicate that gravity compensation ismade only at proximal joints to the base. Dynamic simulations are conducted, and simulation results show that the ratios of gravity compensationare achievable.

중력보상기를 적용한 이족보행로봇 연구

나원현(Won-Hyun Na),최형석(Hyeung-Sik Choi),김동호(Dong-Ho Kim),추우헌(U-Heon Chu) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

In this paper, the structure of a new gravity compensator was studied, and the biped walking robot applying a gravity compensator was presented to improve the performance of the robot. The robot had 13 degree of freedom and is driven by the joint actuator with the gravity compensator. Each leg of the robot is composed of six joints three joints at the hip, a joint at the knee, and two joints at the ankle. The leg of the robot was designed to support 74㎏ weight including 30㎏ payload thanks to the gravity compensator. The performance of the robot was presented by reducing the payload applied to the leg joint of the robot thanks to the gravity compensator.

A Safe Robot Arm with Safe Joints and Gravity Compensator

최동은,최준호,조창현,박신석,강성철 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.2

This study presents a robot arm equipped with safe joints and multi DOFs gravity compensators. The safe joint, also referred to as “Spring-clutch”, is simple passive mechanism that consist of a spring, a cam, and a joint torque sensor. When the torque applied is lower than a pre-set threshold, the Spring-clutch serves as a rigid joint between the input and output. When the applied torque exceeds the threshold, the Spring-clutch is released and is free to rotate like a revolute joint, which significantly re-duces the collision force to avoid damage to the robot, as well as to humans. In addition, a compact joint torque sensor is installed in the Spring-clutch to measure the torque at the joint. Also, the analysis of energy and torque shows that the proposed mechanism can function as a gravity compensator capable of static balancing. Since joint torques vary in accordance with the pose of a manipulator (i.e., rotation angles), a Spring-clutch with a constant threshold torque cannot always guarantee the maximum collision torque in some poses of a manipulator. To overcome this limitation, a gravity compensator is adopted to eliminate the gravitational torque. In this research a bevel gravity compensator is applied which can perform static balancing completely. This paper describes the design principles and fabrication of the safety mechanisms and the robot arm.

종이접기 메커니즘을 사용한 수동 자중 보상 장치

Muhammad Umer Khan,박형순 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

Gravity compensation devices of many different types exist depending upon the amount and type of assistance provided. If we classify the type of assistance provided as vertical abduction, then a device can be designed that allows for free motion in the transverse plane but still allows compensation against gravity. Here the design and construction of one such device is discussed while using the concepts of origami. The device uses a brace design as its base to allow for easy mounting to the user’s body. The actuation mechanism is passive, relying on the inherent stiffness of the material and the stiffness of the origami folds. The basic water bomb origami pattern is used with modifications; reduction of number of mountain folds and introduction of a split fold. The split fold increases the number of stable equilibrium positions ensuring that the user’s arm does not have traverse a long distance between equilibrium positions. Compared to ordinary origami (paper) due to the presence of inherent thickness of materials the device was made by combining a thinner (more flexible) foldable layer and a thicker support layer. The device with this design should allow for comparable deflection in the transverse plane as other soft active gravity compensation devices while complying the requirements of daily living for stroke patients.

하지용 외골격 장치의 설계 연구

최형식(Choi hyeung-sik),전지광(Jeon ji-kwang),홍성율(Hong sung-yul),엄태웅(Uhm tai-woong) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5

This paper is about the design of a new gravity compensator for the exo-skeleton device. The exo-skeleton devices is for increasing the torque of the human body joint for the purpose of helping the disabled or military soldiers. So far, the studied exo-skeleton device is actuated by the motors, but motors are limited in energy such that a short durability is always a big problem. In this paper. a new gravity compensator is proposed to reduce the torque load applied to human body joints due to gravity. The gravity compensator is designed using a tortional bar spring, and its structure and characteristics are studied through the test and computer simulater. Also, a design concept using the gravity compensator of the exo-skeleton device is presented.

음강성을 이용한 중력 보상 보이스코일모터 개발

신부현,함태림,곽대영,이경민 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.8

In this study, a voice coil motor (VCM) with a linear negative stiffness and gravity compensation force was developed. The combination of the developed VCM and spring with linear positive stiffness results in a zero stiffness and the gravity-compensation VCM module was applied. The two stiffnesses cancel out each other, and the resultant stiffness becomes zero. The effects of the design parameters in VCM, such as the armature shape, the position and size of the permanent magnets on the stiffness, the stiffness linearity, and the gravity compensation force, were evaluated. Most of the design parameters were obtained and optimized from the experimental and simulation results. Experimental tests were performed to validate the performance of the designed VCM. Electromagnetic forces were measured at every 1 mm stroke over ± 2 mm stroke, and the stiffness and linearity were calculated. The results were compared with the simulation results. 본 연구에서는 실험 계획법을 이용하여 스트로크 범위에서 선형 음강성과 외부 하중에 대응하는 중력 보상 추력을 발생하는 보이스코일모터를 설계하였다. 선형 음강성 보이스코일모터와 양강성의 스프링을 이용하여 영강성의 중력 보상 보이스코일모터 모듈을 제작할 수 있다. 선형 음강성 특성을 구현하기 위해 실험 계획법과 전자기력 시뮬레이션을 이용하여 아마추어의 내/외측 형상, 상하 및 외곽에 설치되는 영구 자석 크기와 위치, 영구 자석의 성능 오차를 설계 인자로 하여 보이스코일모터의 자기회로를 설계하였다. 최적의 시뮬레이션 결과를 바탕으로 보이스코일모터를 제작하고 실험을 통해 보이스코일모터가 ±2mm 스트로크 범위에서의 목표 사양을 만족하는 음강성, 음강성의 선형성, 중력 보상력을 가지는 것을 확인하였다.