Young-bong Bang

Micro parts assembly system with micro gripper and RCC unit

This paper presents a new micro assembly system, which is composed of a micro gripper, a micro remote center compliance (RCC) unit, a voice coil motor-driving mechanism and precision motion stages. The micro gripper is actuated by two shape memory alloy (SMA) wires, and its grip is 1 mm. The micro RCC unit has low translational and rotational stiffness sufficient for micro parts assembly. The voice coil motor-driving mechanism can generate linear motion with an adjustable stiffness, and it can also measure external force in the moving direction. An algorithm for the automatic assembly of micro parts is also proposed, and assembly experiments are performed.

Development of an Anthropomorphic Robotic Arm and Hand for Interactive Humanoids

Humanoid robots are designed and built to mimic human form and movement. Ultimately, they are meant to resemble the size and physical abilities of a human in order to function in human-oriented environments and to work autonomously but to pose no physical threat to humans. Here, a humanoid robot that resembles a human in appearance and movement is built using powerful actuators paired with gear trains, joint mechanisms, and motor drivers that are all encased in a package no larger than that of the human physique. In this paper, we propose the construction of a humanoid-applicable anthropomorphic 7-DoF arm complete with an 8-DoF hand. The novel mechanical design of this humanoid arm makes it sufficiently compact to be compatible with currently available narrating-model humanoids, and to be sufficiently powerful and flexible to be functional; the number of degrees of freedom endowed in this robotic arm is sufficient for executing a wide range of tasks, including dexterous hand movements. The developed humanoid arm and hand are capable of sensing and interpreting incoming external force using the motor in each joint current without conventional torque sensors. The humanoid arm adopts an algorithm to avoid obstacles and the dexterous hand is capable of grasping objects. The developed robotic arm is suitable for use in an interactive humanoid robot.

Designing a Permanent-Magnetic Actuator for Vacuum Circuit Breakers Using the Taguchi Method and Dynamic Characteristic Analysis

Permanent-magnetic actuators (PMAs) are usually used for vacuum circuit breakers (VCBs) due to their fast linear motion and large holding force. As the holding force becomes larger, so does the current capacity of the circuit breaker. Producing a large holding force with the same PMA size is therefore important in PMA design. This paper presents a design method of a PMA for VCBs. To attain the desired holding force under the restriction of the PMA size, most of the influential PMA yoke design parameters were obtained by the Taguchi method. PMA dynamic characteristics were simulated considering the electromagnetic characteristics, the PMA driving circuit, and the mechanical components connected to the PMA output shaft. Experiments were performed to validate the proposed design method, and the experimental results were compared with the simulation results.

Development of a two-stage high speed electrohydraulic servovalve systems using stack-type piezoelectric elements

This paper presents two systems of two-stage electrohydraulic servo valve with a nozzle-flapper pilot stage, which is controlled by stack-type piezoelectric elements. Two flapper moving mechanisms proposed in this research can compensate for the hysteresis problem and thermal expansion of the piezoelectric elements. The experimental results show that the first flapper moving mechanism has the frequency response of over 500 Hz and the second one has the response of over 600 Hz. And the first simplified servovalve system using the first flapper moving mechanism has the frequency response of about 150 Hz, and the second system has the response of about 300 Hz at the supply pressure of 210 bar.

Initial positioning of a smart actuator using dual absolute encoders

In order to precisely control motor positions, most motor systems use an encoder as the feedback sensor. In the case of a simple system, an incremental encoder and limit switches are used for initial position setting. However, this system loses the current position data when the power goes down and the final position is changed due to an external force. For this reason, absolute encoders are used in full-fledged systems and to facilitate the best performance, a high-resolution absolute encoder should be directly attached at the output axis. However high-resolution absolute encoders are usually large and expensive, and in many cases, it is structurally difficult to directly install the absolute encoder to the output axis. An alternative to this direct sensing of the output angle is a multiturn absolute encoder, which is attached to the motor shaft. However, the multiturn absolute encoder also loses its position data when the backup battery runs out and an external force is applied. In this paper, we therefore suggest a dual absolute encoder system, in which one absolute encoder is attached to the motor shaft and the other low-resolution absolute encoder is attached to the output shaft of the harmonic drive speed reducer (the output shaft of a smart actuator). The required conditions for the errorless operation of this dual encoder system are derived and verified by simulations and experiments.

An earthworm-like actuator using segmented solenoids

A biomimetic actuator is developed using four segmented solenoids mimicking earthworm locomotion. The proposed actuator not only has a simple structure composed of cores and coils, but also enables bi-directional actuation and high speed locomotion regardless of friction conditions. We have implemented theoretical analysis to design the optimal profiles of input current signal for maximum speed and predict the output force and stroke. Experiments using a prototype show that the earthworm-like actuator travels with a speed above 60 mm s−1 regardless of friction conditions.

A compact stair-climbing wheelchair with two 3-DOF legs and a 1-DOF base

Purpose – The purpose of this paper is to describe a compact wheelchair, which has two 3-degrees of freedom (DOF) legs and a 1-DOF base (the total DOF of the leg system is 7) for stair-climbing, and wheels for flat surface driving. Design/methodology/approach – The proposed wheelchair climbs stairs using the two 3-DOF legs with boomerang-shaped feet. The leg mechanisms are folded into the compact wheelchair body when the wheelchair moves over flat surfaces. The authors also propose a simple estimation method of stair shape using laser distance sensors, and a dual motor driving system to increase joint power. Findings – The proposed wheelchair can climb arbitrary height and width stairs by itself, even when they are slightly curved. During climbing, the trajectory of the seat position is linear to guarantee the comfort of rider, and the wheelchair always keeps a stable condition to ensure the stability in an emergency stop. Originality/value – The wheelchair mechanism with foldable legs and driving wheels ...

Power-Assisted Wheelchair With Gravity and Friction Compensation

In this paper, a gravity compensated power-assisted wheelchair (GCPAW) is proposed, which will climb a hill, and stop, and make as a delicate movement in the middle of the hill as it can do on a flat surface. To climb the hill, the proposed GCPAW compensates for the parallel component of the force of gravity (the force that causes acceleration or deceleration) on a hill. A tilt sensor measures the angle of the inclined plane and electric clutches automatically connect and disconnect drive mechanisms with the wheels. The GCPAW also compensates for friction in the drive mechanism that would cause additional resistance. The rider propels the GCPAW in the same way that he/she would propel a manual wheelchair, but the mechanism compensates for both gravity and the friction. Additionally, overcompensation for the friction helps the riders propulsion, so that with the same propulsion force the rider travels further than in a manual wheelchair, resulting in an easier movement for the rider.

Surface coating for prevention of metallic seed migration in tissues

PURPOSE In radiotherapy, metallic implants often detach from their deposited sites and migrate to other locations. This undesirable migration could cause inadequate dose coverage for permanent brachytherapy and difficulties in image-guided radiation delivery for patients. To prevent migration of implanted seeds, the authors propose a potential strategy to use a biocompatible and tissue-adhesive material called polydopamine. METHODS In this study, nonradioactive dummy seeds that have the same geometry and composition as commercial I-125 seeds were coated in polydopamine. Using scanning electron microscopy and x-ray photoelectron spectroscopy, the surface of the polydopamine-coated and noncoated seeds was characterized. The detachment stress between the two types of seeds and the tissue was measured. The efficacy of polydopamine-coated seed was investigated through in vitro migration tests by tracing the seed location after tissue implantation and shaking for given times. The cytotoxicity of the polydopamine coating was also evaluated. RESULTS The results of the coating characterization have shown that polydopamine was successfully coated on the surface of the seeds. In the adhesion test, the polydopamine-coated seeds had 2.1-fold greater detachment stress than noncoated seeds. From the in vitro test, it was determined that the polydopamine-coated seed migrated shorter distances than the noncoated seed. This difference was increased with a greater length of time after implantation. CONCLUSIONS The authors suggest that polydopamine coating is an effective technique to prevent migration of implanted seeds, especially for permanent prostate brachytherapy.

Design and fabrication of high-power smart actuator module

In building a prototype for robot research, it is very useful to use smart actuator modules that include an electric motor, a reducer, and a controller. These modules help maintain low costs, short development times, and high reliability. However, smart actuator modules in the market are limited in their application to building small robots, because most have a low power, i.e., lower than 10 W. This paper presents a high-power actuator module, which can be used for building child-sized robots. The modules mass is 1.3 kg, and its maximum power is 200 W, with a maximum torque of 50 N·m. Further, it can be installed in various ways to produce many different joint structures.