Gab-Soon Kim

Gait pattern generation with knee stretch motion for biped robot using toe and heel joints

This paper presents a new alternative methodology to generate gait pattern with a knee stretched motion for biped robot utilizing toe and heel joints. During walking sequence, human heels act as passive joints that create some support area which enhances the stability of human walking. This research tries to replace human-heel like mechanism with a heel joint in the biped robot foot. The existence of heel joints in the biped robot feet has two main advantages. The first one is that the support area during double support phase will be increased. Secondly, singularity during knee stretch motion can be avoided. The loss of degree of freedom in the knee joint will not produce singularity in the inverse kinematics solution since there is still another degree of freedom in the heel joint. The effectiveness of the algorithm is being studied through a dynamic simulation tool. A stable knee stretch walking pattern utilizing toe and heel joints was generated, which has some similarity to the human walking pattern. Effectiveness of the proposed algorithm in terms of joint torque requirements as well as energy consumptions have also been shown.

The design of a six-component force/moment sensor and evaluation of its uncertainty

This paper describes the development of a six-component force/moment sensor with plate beams which may be used in industry for measuring forces F x , F y and F z and moments M x , M y and M z simultaneously and the evaluation of its relative expanded uncertainty. In order to develop the six-component force/moment sensor with small capacity (F x of the sensor (x-direction force sensor), F y and F z are each 100 N, M x of the sensor (x-direction moment sensor) and M x are I N m, M z is 2 N m), the structure of such a sensing element for the six-component force/moment sensor is newly modelled, designed and manufactured. Also, methods for calibration and evaluation of the relative expanded uncertainty are newly proposed. The six-component force/moment sensor developed here is calibrated with the proposed calibration method and the relative expanded uncertainty is evaluated using the proposed uncertainty evaluation method and the calibration results. This reveals that the relative expanded uncertainty of the six-component force/moment sensor is less than 2.78%. Thus, it is thought that this six-component force/moment sensor can be usefully used in industry and that the methods for calibration and evaluation of the uncertainty can also be used for calibration and evaluation of the uncertainty of the multi-component force/moment sensor.

Development of a small 6-axis force/moment sensor for robot's fingers

This paper describes the development of a small 6-axis force/moment sensor for robots fingers (grippers), which detects forces Fx, Fy and Fz, and moments Mx, My and Mz, simultaneously. In order to safely grasp an unknown object using the robots fingers, and accurately perceive its position in the fingers, it should measure the force in the gripping direction, the force in the gravity direction and moments in each direction, and perform the force control using the measured forces and moments. Also, it should detect moments Mx (x-direction moment), My and Mz to accurately perceive the position of the object in the fingers. Thus, the robots fingers should be composed of 6-axis force/moment sensors that can measure forces Fx, Fy and Fz, and moments Mx, My and Mz, simultaneously. It is very important for the 6-axis force/moment sensor for an intelligent robots fingers to be of small size in its body and in its interference errors. Therefore, the new modelling of a small 6-axis force/moment sensor is needed. In this paper, the small 6-axis force/moment sensor for measuring forces Fx, Fy and Fz, and moments Mx, My and Mz simultaneously was newly modelled using several parallel-plate beams (PPBs), designed and fabricated. A characteristic test of the made sensor was performed, and the result shows that the interference errors of the developed sensor are less than 3.93%. Thus, the developed small 6-axis force/moment sensor can be used for robots fingers.

The development of a six-component force/moment sensor testing machine and evaluation of its uncertainty

This paper describes the design and fabrication of a six-component force/moment sensor testing machine and the evaluation of its uncertainty. This testing machine, which generates forces Fx (x-direction force), Fy and Fz from 50 to 500 N each and moments Mx (x-direction moment), My and Mz from 5 to 50 N m each, simultaneously or separately, consists of a body, a fixture, a force generating system, a moment generating system, weights and a control system. Forces and moments are automatically generated by the control system composed of a computer, three step motors and so on. Also, the relative expanded uncertainty of the testing machine is evaluated. The results show that the relative uncertainties for force components ±Fx and ±Fy and moment components ±Mx and ±My are less than 8.6×10-4 and those for force components + Fz and -Fz and moment components ±Mz are less than 1.7×10-3, 1.2×10-5 and 1.7×10-3 respectively.

The simplest passive dynamic walking model with toed feet: A parametric study

This paper presents a passive dynamic walking model with toed feet that can walk down a gentle slope under the action of gravity alone. The model is the simplest of its kind with a point mass at the hip and two rigid legs each hinged at the hip on the one end and equipped with toed foot on the other end. We investigate two cases of the model, one with massless legs and another with infinitesimal leg masses. Rotation of the stance foot about the toe joint is initiated by ankle-strike, which is caused by the inelastic collision of the stance leg with a stop mounted on the stance foot. Numerical simulations of walking show that larger step lengths, higher speeds, stability, and energy efficiency can be achieved than what is achievable by a point-feet walker of same hip mass and leg lengths. Period-two gait of a point-feet walker is compared with period-one gait of the toed-feet walker and the mechanism responsible for achieving longer step lengths is described. It is shown that the advantage of the proposed walker comes from its relation to arc-feet walker. The characteristics of deterministic gait with infinitesimal leg masses is compared with that of nondeterministic gait with zero leg masses. It is shown that deterministic gait does not give maximum speed and efficiency compared to nondeterministic gait with swing leg control. Finally, active dynamic walking of the proposed walker is discussed.

Reliability of the Pinch Strength with Digitalized Pinch Dynamometer

Objective To examine the intra-rater, inter-rater, and inter-instrumental reliability of the digitalized pinch muscle strength dynamometer. Method Thirty normal subjects were examined for pinch strength, using both the Preston pinch gauge and the digitalized pinch dynamometer. The participants performed all pinch strength tests in the seated position as recommended by the American Society of Hand Therapists (ASHT). Three successive measurements were taken for each hand. The mean of the three trials was used for data analysis. The pinch strength tests performed used a repeated measure design and measurements were taken by each rater. Results The relationship between the Preston pinch gauge and the digitalized pinch dynamometer in pinch strength was reliable (the ICC were 0.821 and 0.785 in rater 1 and rater 2 respectively). The relationship between the first session and second session in pinch strength using the digitalized pinch dynamometer was reliable (the ICC were 0.872 and 0.886 in rater A and rater B respectively). The relationship between rater A and rater B in pinch strength using the digitalized pinch dynamometer was reliable (the ICC was 0.754). Conclusion The pinch strength measurement using the digitalized pinch dynamometer is reliable within the rater and between raters. Thus, the Preston pinch gauge and the digitalized dynamometer measure grip strength equivalently, and can be used interchangeably.

Development of Intelligent Robot's Hand with Three-Axis Finger Force Sensors for Intelligent Robot

This paper describes the intelligent robot’s hand with three-axis finger force sensors for an intelligent robot. In order to grasp an unknown object safely, it should measure the mass of the object, and determine the grasping force using the mass, then control the robot’s fingers with the grasping force. In this paper, the intelligent robot’s hand for an intelligent robot was developed. First, the three-axis finger force sensors were designed and manufactured, second, the intelligent robot’s hand with three-axis finger force sensors were designed and fabricated, third, the high-speed control system was designed and manufactured using DSP(digital signal processor), finally, the characteristic test to grasp an unknown object safely was carried out. It was confirmed that the developed intelligent robot’s hand could grasp an unknown object safely.

Development of Two-Finger Force Measuring System to Measure Two-Finger Gripping Force and Its Characteristic Evaluation

Finger patients can`t use their hands because of the paralysis their fingers. Their fingers are recovered by rehabilitating training, and the rehabilitating extent can be judged by measuring the pressing force to be contacted with two fingers(thumb and first finger, thumb and middle finger, thumb and ring finger, thumb and little finger). At present, most hospitals have used a thin plastic-plate for measuring the two-finger grasping force, and we can only judge that they can grasp the plate with their two-finger through it, because the plate can`t measure the two-finger grasping force. But, recently, the force measuring system for measuring two-finger grasping force was developed using three-axis force sensor, but it is very expensive, because it has a three-axis force sensor. In this paper, two-finger force measuring system with a one-axis force sensor which can measure two-finger grasping force was developed. The one-axis force sensor was designed and fabricated, and the force measuring device was designed and manufactured using DSP(Digital Signal Processing). Also, the grasping force test of men was performed using the developed two-finger force measuring system, it was confirmed that the grasping forces of men were different according to grasping methods, and the system can be used for measuring two-finger grasping force.

Development of Force Measuring System using Three-axis Force Sensor for Measuring Two-finger Force

Stroke patients can`t use their hands because of the paralysis their fingers. Their fingers are recovered by rehabilitating training, and the rehabilitating extent can be judged by measuring the pressing force to be contacted with two fingers (thumb and first finger, thumb and middle finger, thumb and ring finger, thumb and little finger). But, at present, the grasping finger force of two-finger can`t be accurately measured, because there is not a proper finger-force measuring system. Therefore, doctors can`t correctly judge the rehabilitating extent. So, the finger-force measuring system which can measure the grasping force of two-finger must be developed. In this paper, the finger-force measuring system with a three-axis force sensor which can measure the pressing force was developed. The three-axis force sensor was designed and fabricated, and the force measuring device was designed and manufactured using DSP (Digital Signal Processing). Also, the grasping force test of men was performed using the developed finger-force measuring system, it was confirmed that the grasping forces of men were different according to grasping methods.

Development of 6-axis Force/Moment Sensor for Humanoid Robot's Foot

This paper describes the development of 6-axis force/moment sensor considered humanoid robots weight for an intelligent foot of humanoid robot. In order to walk on uneven terrain safely, the foot should perceive the applied forces Fx, Fy, Fz and moments Mx, My, Mz to itself, and control the foot using the forces and moments. The applied forces and moments should be measured from a 6-axis force/moment sensor attached to the foot, the sensor is composed of Fx sensor, Fy sensor, Fz sensor, Mx sensor, My sensor and Mz sensor in a body (single block). In this paper, a 6-axis force/moment sensor for perceiving forces and moments in a humanoid robots foot was developed using many PPBs (parallel plate-beams). The structure of the sensor was newly modeled, and the sensing elements (plate-beams) of the sensor were designed using FEM (Finite Element Method). Then the 6-axis force/moment sensor was fabricated by attaching strain-gages on the sensing elements, and the characteristic test of the developed sensor was carried out. The rated outputs from FEM analysis agree well with that from the characteristic test.