• Journal of Advanced Marine Engineering and Technology
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• v.33 no.2
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• pp.226-232
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• 2009

In this paper, a design and analysis of a gravity compensator which is a new device to reduce the joint torque of robots caused due to gravity is presented. Joints of all robots are loaded by large torques due to gravity. By applying the gravity compensator to the robot joints, the load torques applied to the robot joints are reduced by the repulsive force of the gravity compensator such that the size of the joint actuation motor can be reduced. In this paper, the structure and force relation of the gravity compensator are analyzed. The superior performance of the proposed gravity compensator is verified through experiments which measure the joint motor current caused by the load applied to the robot link.

• Animal cells and systems
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• v.4 no.3
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• pp.201-214
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• 2000

Two quite different types of plant cells are analysed with regard to transduction of the gravity stimulus: (i) Unicellular rhizoids and protonemata of characean green algae; these are tube-like, tip-growing cells which respond to the direction of gravity. (ii) Columella cells located in the center of the root cap of higher plants; these cells (statocytes) perceive gravity. The two cell types contain heavy particles or organelles (sataoliths) which sediment in the field of gravity, thereby inducing the graviresponse. Both cell types were studied under microgravity conditions ($10^{-4}$/ g) in sounding rockets or spacelabs. From video microscopy of living Chara cells and different experiments with both cell types it was concluded that the position of statoliths depends on the balance of two forces, i.e. the gravitational force and the counteracting force mediated by actin microfilaments. The actomyosin system may be the missing link between the gravity-dependent movement of statoliths and the gravity receptor(s); it may also function as an amplifier.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.883-888
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• 2011

Laparoscopic surgery is being used in various surgical fields because it minimizes scarring. Laparoscopic operations require practical hand skills, so surgeons train on animals and via surgery training tool sets. However, these tool sets do not give the surgeon the sensation of touching real organs. A recently developed laparoscope simulator has a high friction force along the translational axis and a high gravity force along the pitch axis, and therefore it does not permit the operator to control his or her hands delecately. In the paper, the friction force along the axes is auumed to depend on the veolcity, and the gravity force on the angle and distance. We develop a compensation model that combines the gravity and friction force models.

• Advances in Computational Design
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• v.4 no.2
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• pp.141-153
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• 2019

This research is comprised of virtually simulating behavior while experiencing low gravity effects in advance of real world testing in low gravity aboard Zero Gravity Corporation's (Zero-G) research aircraft (727-200F). The experiment simulated a drill rig penetrating a regolith simulant. Regolith is a layer of loose, heterogeneous superficial deposits covering solid rock on surfaces of the Earth' moon, asteroids and Mars. The behavior and propagation of space debris when drilled in low gravity was tested through simulations and visualization in a leading dynamic simulation software as well as discrete element modeling software and in preparation for comparing to real world results from flying the experiment aboard Zero-G. The study of outer space regolith could lead to deeper scientific knowledge of extra-terrestrial surfaces, which could lead us to breakthroughs with respect to space mining or in-situ resource utilization (ISRU). These studies aimed to test and evaluate the drilling process in low to zero gravity environments and to determine static stress analysis on the drill when tested in low gravity environments. These tests and simulations were conducted by a team from Texas A&M University's Department of Construction Science, the United States Air Force Academy's Department of Astronautical Engineering, and Crow Industries

• The Journal of Korean Physical Therapy
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• v.11 no.1
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• pp.63-70
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• 1999

This study was for mathematical method of calculating the joint reaction force during on single - leg stance on a normal and hemiplegic patients. It is important to compare the distance of the line of gravity from the hip joint on hemiplegic patients with this on normal in this study. In earlier studies, there is no include the concept about biomechanical analysis on the shin of line of gravity of hemiplegic patients. Though this concept, we found the compensation make the line of gravity closer to the supporting hip joint and the trunk was toward the side of paralysis. The result of the Joint reaction force on hemiplegic patients is found to be approximately $31.33\%$ in the unaffected side by biomechanical analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.229-232
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• 2002

This paper describes the development of robot's finger 3-axis force sensor that detects the Fx, Fy, and Fz simultaneously fur stably grasping an unknown object. In order to safely grasp an unknown object using the robot's fingers, they should detect the force of gripping direction and the force of gravity direction, and perform the force control using the detected farces. The 3-axis force sensor that detects the Fx, Fy, and Fz simultaneously should be used for accurately detecting the weight of an unknown object of gravity direction. Thus, in this paper, robot's finger for stably grasping an unknown object is developed. And, the 3-axis farce sensor that detects the Fx, Fy, and Fz simultaneously fur constructing a robot's finger is newly modeled using several parallel-plate beams, and is fabricated. Also, it is calibrated, and evaluated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.393-397
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• 1996

A stewart platform-based force/torque sensor with 6 elastic legs was designed and manufactured Kinematic design parameters were determined so that the force/torque sensor might have the isotropic force/torque properities. In a force/torque analysis, it was used the solution of forward kinematics by linearization of the solution of the inverse kinematics. The performance of te force/torque sensor was investigated by measurement experiments. The gravity compensation was conducted to reduce the force and torque effects by the weights of the upper plate, joints and other sensor parts.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.1
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• pp.78-83
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• 1997

The paper presents the experimental analysis of a Stewart platform-based force-torque senor. The closed-form solution of forward kinematics of the Stewart platform is derived approximately by way of a linearization technique, and the solution is used in the force analysis of the force-torque sensor. An exper- mental studies show that the proposed method including gravity compensation algorithm is valid for Stew- art platform-based force-torque sensors. The performance of the developed force-torque sensor is evaluated in view of accuracy and linearity in measurements.

• Current Industrial and Technological Trends in Aerospace
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• v.8 no.1
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• pp.96-103
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• 2010

The propulsion systems such as upper stages of launch vehicles, orbiters, spacecrafts have to operate in the zero gravity environment. Because the flight condition where the vehicle undergoes is different from the normal gravity state, many studies have been being in progress. Fluid behavior in the zero gravity condition is differently shown in the normal gravity state because the importance of the intermolecular force, such as adhesion, cohesion, and surface tension is enlarged. In this paper, we investigate the characteristic of fluid behavior and describe effects and problems on the liquid propulsion system due to these fluid behavior. We also check which studies are in progress in order to solve these problems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.573-576
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• 2010

The propulsion systems such as upper stages of launch vehicles, orbiters, spacecrafts have to operate in the zero gravity environment. Because the flight condition where the vehicle undergoes is different from the normal gravity state, many studies have been being in progress. Fluid behavior in the zero gravity condition is differently shown in the normal gravity state because the importance of the intermolecular force, such as adhesion, cohesion, and surface tension is enlarged. In this paper, we investigate the characteristic of fluid behavior and describe effects and problems on the liquid propulsion system due to these fluid behavior. We also check which studies are in progress in order to solve these problems.