Most existing mechanical gravity compensators have been developed for revolute joints that are found in majority of articulated robot arms. However, robots such as patient transport robots use prismatic joints, which need to handle a heavy payload. In this study, a high-capacity linear gravity compensator (LGC), which comprises pure mechanical components, such as coil springs, a rack-pinion gear, a cam, and a wire, is proposed to compensate for the payload applied to a prismatic joint. The LGC is designed to generate a constant compensation force regardless of the payload position. The device can be manufactured at a low cost and has a significantly long lifespan because it uses coil springs to serve as an elastic body. Experiments demonstrate that the robot with the LGC can handle a load of 100 kg more than the robot using the same motors without it.

The use of high-capacity motors and harmonic drives increases the manufacturing cost and the energy consumption of the robot. It is well known that most motor torques are used to support the robot mass and payload. To deal with this problem, we propose a wall-mounted 3-DOF roll-pitch-pitch counterbalance mechanism (CBM). Unlike previous CBMs used for floor-mounted industrial robot arms, the proposed CBM can be applied to wall-mounted robots in which the first three joints are all coupled and affected by gravity. This mechanism is composed of pure mechanical components such as coil springs, differential gear structure, and belt-pulley system. A 6-DOF robot arm equipped with the proposed CBM was fabricated to verify the performance of gravity compensation. It is shown that the proposed 3-DOF CBM can effectively compensate for gravitational torques, thus drastically reducing the motor torques required to operate the robot.

Most collaborative robots use high-power motors for a good weight-to-payload ratio, thus leading to not only an increase in manufacturing cost but also possibility of injury at a collision between a human and a robot. To maintain high-performance with low-power driving units, a spring-based counterbalance mechanism (CBM) and a robot arm based on these CBMs were developed in our previous study. In this study, a 6-DOF collaborative robot equipped with a multi-DOF CBM is proposed. A double parallelogram linkage and a slider-crank mechanism are employed for a compact and durable design of a multi-DOF CBM. Unlike the previous prototypes in which some portions of CBMs were protruded out of the robot body due to their large volume, the proposed CBMs can be embedded inside the robot links. The performance of the developed CBM and collaborative robot were verified based on simulations using dynamic simulation software. Simulation results show that the proposed CBMs can effectively reduce the joint torques required to operate the robot. This reduction in the torque enables low-power motors to be used in a collaborative robot, thus significantly improving collision safety and energy efficiency.

In most 6 DOF robot arms, considerable amounts of gravitational torques due to the robot's own weight are applied to pitch joints of the robot, which causes most arms to use high capacity motors and speed reducers. A spring-based counterbalance mechanism can compensate for this gravitational torque, thus leading to a significant reduction in the effect of gravity. However, a simple installation of counterbalance mechanisms at each pitch joint does not work properly because the gravitational torque at each joint is dependent also on the other joints. To achieve multi-DOF counterbalancing, we propose a parallelogram linkage combined with dual counterbalance mechanisms, each being composed of a slider-crank mechanism and springs. Simulations and experimental results showed that the counterbalance robot arm based on the proposed counterbalance mechanisms effectively reduced the torques required to support the robot mass, thus allowing the prospective use of much smaller motors and speed reducers than traditional industrial robots.

In recent years, much research has been done to develop various direct teaching schemes, in which an operator directly teaches a robot by hand guiding instead of using a teach pendant. However, conventional direct teaching methods are usually sensor based, thus leading to an expensive solution. To deal with this problem, this study proposes a sensorless hand guiding method based on torque control. The dynamic model of a robot along with the motor current and friction model is used to determine the user's intention to move the end-effector of a robot instead of directly sensing the external force by the user. A friction torque observer is employed for the friction model identification. The proposed method was experimentally verified using a 6 DOF robot. The experimental results show that the proposed sensorless hand guiding scheme is quite useful for practical direct teaching although the sensitivity is slightly lower than the sensor-based approach.

Low-cost but high-performance robot arms are required for robot arms to come into widespread use. To provide sufficient torques to support the robot mass and payload, most arms use expensive motors and speed reducers, which are the main reasons for their high price. As a solution to these problems, a multiple-degree-of-freedom (DOF) counterbalance mechanism and robot arm were developed in our previous study, which can compensate for the gravitational torque due to the robot mass. However, there are durability and reliability problems associated with wire-based mechanisms. To solve these, in this study, we proposed a new counterbalance mechanism based on a spring and slider-crank mechanism, along with a double-parallelogram mechanism composed of bevel gear units. Moreover, a 6-DOF counterbalance robot arm was built to verify the performance of the proposed mechanism. Simulation and experimental results showed that the proposed mechanism effectively decreased the torque required to support the robot mass, thus allowing the prospective use of low-cost motors and speed reducers for high-performance robots.

As there have been many attempts for human-robot collaborations, various solutions to collision detection have been proposed in order to deal with safety issues. However, existing methods for collision detection include the usage of skin sensors or joint torque sensors, and cannot be applied to robots without these sensors such as industrial manipulators. In this study we propose a sensorless collision detection method. The proposed method detects the collision between robots and humans by identifying the external torques applied to the robot. Without using extra sensors, we observed the joint friction model and motor current. We have formulated the friction model for the robot by using the dynamics of the robot and the observer based on the generalized momentum. In addition, formulation of the friction model and the identification scheme did not include any use of extra sensors. The performance of the proposed collision detection method was evaluated using a 7 DOF manipulator. The experimental results show that collision can be reliably detected without any extra sensors for any type of robot arm.

To prevent the failure of peg-in-hole assembly tasks involving geometrically complex parts, a force control-based assembly strategy that takes geometric information into account is required. Therefore, in this study, we propose an assembly strategy for complex-shaped parts which performs force control based on visually-obtained geometric information and CAD models. CAD models are used to obtain geometric information about the parts, and a camera is used to track their position and orientation. In addition, an impedance control scheme is used to control the contact force to avoid excessive force during assembly tasks. The performance of the proposed guidance algorithm was evaluated by a series of experiments using arbitrary complex-shaped parts.

This study presents an upward-looking camera-based global localization scheme using the position and orientation of ceiling features. If the robot pose is unknown, the region-based ceiling features from the current image are matched to a pre-built feature map from the RBPF-based SLAM process. Then, the candidate areas of the real robot pose are set around the matched features. The candidates are represented by two spots for the features having both position and orientation, while by a circle if they have only position. Finally, the real robot pose is determined at the intersection point. The candidate areas are realistically modeled by applying the observation error, and useless candidates are significantly reduced by considering the feature orientation. Several experiments in real environments validated the effectiveness of the proposed global localization scheme.

Low-cost but high performance robot arms are required for widespread use of service robots. Most robot arms use expensive motors and speed reducers to provide torques sufficient to support the robot mass and payload. If the gravitational torques due to the robot mass, which is usually much greater than the payload, can be compensated by some means, the robot would need much smaller torques, which can be delivered by cheap actuator modules. To this end, we propose a counterbalance mechanism which can completely counterbalance the gravitational torques due to the robot mass. Since most 6 DOF robots have 3 pitch joints, which are subject to gravitational torques due to the robot mass, we propose a 3 DOF counterbalance mechanism based on the double parallelogram mechanism, in which reference planes are provided to each joint for proper counterbalancing. A 5 DOF counterbalance robot arm was built to demonstrate the performance of the proposed mechanism. Simulation and experimental results showed that the proposed mechanism had effectively decreased the torque required to support the robot mass, thus allowing the prospective use of low-cost motors and speed reducers for high performance root arms.

Human-robot collision has drawn increasing attention in recent years and collision safety can be improved by successfully detecting collisions between a human and a robot. For a manipulator working in human environments, collisions usually occur at the manipulator body while the robot performs a contact task using its end-effector to interact with the environment. Therefore, both collision force and the force on the end-effector contribute to the external torques which can be estimated from the robot dynamics and the joint torques measured by the joint torque sensors, which means whether or not a collision has occurred cannot be reliably determined using this estimation. In this study, we propose a novel collision detection index to detect collisions independently of the end-effector force of a redundant manipulator equipped with joint torque sensors. Using the null space projection of a redundant manipulator, the collision detection index can be expressed as a function of the torque generated by a collision and the manipulator configuration. The proposed index is verified through various simulations. Simulation results show that collisions can be reliably detected regardless of the presence of the end-effector forces even in situations with external torques contaminated by substantial error.

In recent years, collision safety between a human and a robot has been increasingly important along with the spread of service robots. Much research has been conducted on how to design a safe manipulator, but it is not applicable to real manipulators yet. To deal with this problem, we propose a guideline to design a safe manipulator, which is composed of two phases, the safety evaluation and design parameter adjustment. To evaluate collision safety, we adopt the effective mass and manipulability and simplify the spatial collision between a human and a multi-DOF manipulator. Moreover, the experimental results from the biomechanical literature are employed for more realistic evaluation of collision safety. The design parameters and proper adjustment strategy can be established based on the safety evaluation results, and the design parameters of a manipulator can be modified to satisfy the collision safety and design requirement. The proposed guideline is implemented in the design of a 3 DOF safe manipulator, and it is shown that this guideline can be used to design a multi-DOF safe manipulator.

For tasks that require robot-environment interaction, stiffness control is important to ensure stable contact motion and collision safety. The variable stiffness approach has been used to address this type of control. We propose a hybrid variable stiffness actuator (HVSA), which is a variable stiffness unit design. The proposed HVSA is composed of a hybrid control module based on an adjustable moment-arm mechanism, and a drive module with two motors. By controlling the relative motion of gears in the hybrid control module, position and stiffness of a joint can be simultaneously controlled. The HVSA provides a wide range of joint stiffness due to the nonlinearity provided by the adjustable moment arm. Furthermore, the rigid mode, which behaves as a conventional stiff joint, can be implemented to improve positioning accuracy when a robot handles a heavy object. In this paper, the mechanical design features and related analysis are explained. We show that the HVSA can provide a wide range of stiffness and rapid responses according to changes in the stiffness of a joint under varying loads by experiments. The effectiveness of the rigid mode is verified by some experiments on position tracking under high-load conditions.

For tasks requiring robot-environment interaction, compliant motion is important to ensure stable contact and operational safety. The compliant actuators such as a series elastic actuator and a variable stiffness actuator (VSA) are expected to be one of the promising solutions to provide a compliant motion. In this paper, we propose a gripper actuated by the hybrid variable stiffness actuator developed in our previous work to show how the VSA can improve the ability of grasping. The gripper, which is equipped with two symmetric 4-bar linkages, can conduct the position and stiffness control simultaneously, and the grasping force can be calculated by the estimated torque of the HVSA. The HVSA-actuated gripper is able to grasp fragile objects with compliant motion and the relatively heavy object with stiff motion. Furthermore, the features of the variable stiffness provide operational safety by adjusting the stiffness according to the task. In this study, the relationships between the joint torque and the grasping force, and between the joint stiffness and the Cartesian stiffness are analyzed to control the grasping force. From a series of experiments, it is shown that the gripper can grasp fragile objects such as an egg and a wine glass, as well as relatively heavy object without any soft cover and force/torque sensor.

Modeling of low severity soft-tissue injury due to unwanted collisions of a robot in collaborative settings is an important aspect to be treated in safe physical Human-Robot Interaction (pHRI). Up to now, safety evaluations for pHRI were mainly conducted by using safety criteria related with impact forces and head accelerations. These indicate severe injury in the robotics context and leave out low severity injury such as contusions and lacerations. However, for the design of an intrinsically safer robot arm, a reliable evaluation of the collision between a human and a robot that is based on skin injury criteria is essential. In this paper, we propose a novel human-robot collision model with and without covering, which is based on the impact stress distribution. The reliability of the proposed collision model is verified by a comparison with various cadaver experiments taken from existing biomechanical literature. Since the stress characteristics acting on the human head can be analyzed with this new collision model, the occurrence of certain soft-tissue injury can be estimated. Furthermore, the method serves for selecting the appropriate covering parameters, as e.g. elastic modulus and thickness, by evaluating the chosen skin injury indices.

For tasks requiring robot-environment interaction, stiffness control is important to ensure both stable contact motion and collision safety. The variable stiffness approach has been used to address this problem. We propose a hybrid dual actuator unit (HDAU) which is a novel variable stiffness unit design. The HDAU is composed of a hybrid control module based on an adjustable moment arm mechanism and a drive module with two motors. By controlling the relative motion of gears in the hybrid control module, position and stiffness can be simultaneously controlled for the same joint. The HDAU provides a wide range of joint stiffness due to nonlinearity obtained from the adjustable moment arm. The joint stiffness can be kept constant independent of the passive deflection angle of the output shaft. Furthermore, stable interaction can also be achieved because the joint stiffness is indirectly adjusted by position control of the hybrid control module. The characteristics of the HDAU are analyzed in this study. We show by experiment that the HDAU can provide a wide range of stiffness variation and rapid response for stiffness change.

In recent years, the potential for collision between humans and robots has drawn much attention since service robots are increasingly being used in the human environment. A safe robot arm can be achieved using either an active or passive compliance method. A passive compliance system composed of purely mechanical elements often provides faster and more reliable responses to dynamic collision than an active system involving sensors and actuators. Since positioning accuracy and collision safety of a robot arm are equally important, a robot arm should have very low stiffness when subjected to a collision force capable of causing human injury. Otherwise, it should maintain a very high stiffness. To implement these requirements, a novel safe joint mechanism (SJM-III) consisting of an inclined link, a slider with rollers, and linear springs is proposed. The SJM-III has the advantage of nonlinear stiffness, which can be achieved only with passive mechanical elements. Various analyses and experiments on static and dynamic collisions show high stiffness of the SJM-III against an external torque less than a predetermined threshold torque, with an abrupt drop in stiffness when the external torque exceeds this threshold. The safe joint mechanism enables a robot manipulator to guarantee positioning accuracy and collision safety, and which is simple to install between an actuator and a robot link without a significant change in the robot's design.

Not all line or point features capable of being extracted by sonar sensors from cluttered home environments are useful for simultaneous localization and mapping (SLAM) due to their ambiguity. We present a new sonar feature structure suitable for a cluttered environment and the extended Kalman filter (EKF)-based SLAM scheme. The key concept is to extract circle feature clouds on salient convex objects by sonar data association. The centroid of each circle cloud, called a sonar salient feature, is used as a natural landmark for EKF-based SLAM. After completing initial exploration in an unknown environment, SLAM-able areas with sonar salient features can be defined, and cylindrical objects are placed conveniently at weak SLAM-able areas as a supplemental environmental saliency to enhance SLAM performance. Experimental results demonstrate the validity and robustness of the proposed sonar salient feature structure for EKF-based SLAM.

Collision safety between humans and robots has drawn much attention since service robots are increasingly being used in human environments. A safe robot arm based on passive compliance can usually provide faster and more reliable responses for dynamic collision than an active one involving sensors and actuators. Since both positioning accuracy and collision safety of the robot arm are equally important, a robot arm should have very low stiffness when subjected to a collision force greater than the injury tolerance, but should otherwise maintain very high stiffness. To implement these requirements, a novel safe joint mechanism (SJM-II) which has much smaller size and lighter weight than the previous model, is proposed in this research. The SJM-II has the advantage of nonlinear spring which is achieved using only passive mechanical elements such as linear springs and a double-slider mechanism. Various analyses and experiments on static and dynamic collisions show that stiffness of the SJM-II is kept very high against an external torque less than the predetermined threshold torque, but abruptly drops when the input torque exceeds this threshold, thereby guaranteeing positioning accuracy and collision safety. Furthermore, a robot arm with two SJM-IIs is verified to achieve collision safety in 2D space.

In recent years, collision safety has been one of the most important issues for service robots. To ensure collision safety assurance, a passive compliance method is preferred to an active one because it can provide faster and more reliable responses to dynamic collision. Since both positioning accuracy and collision safety are equally important, a robot arm should have very low stiffness when subjected to a collision force greater than the one causing human injury, but maintain very high stiffness otherwise. In order to realize these ideal features, a novel safe joint mechanism (SJM) composed of linear springs and a modified slider-crank mechanism is proposed in this paper. The SJM has the advantages of variable stiffness which can be achieved only by passive mechanical elements. Various experiments on static and dynamic collisions show the high stiffness of the SJM against an external force of less than the critical impact force, but an abrupt drop in the stiffness when the external force exceeds this critical force, which guarantees positioning accuracy and collision safety. Furthermore, the critical impact force can be set to any value depending on the application and the environment.

Over the past few decades, various haptic gloves have been developed for use in virtual environments. The actuating systems for most existing haptic gloves require lots of external auxiliary equipment. Because of this, the motion of the user is restricted by the length of the electric wires or pneumatic tubes attached to this equipment. A compact actuation system, including related equipment, is thus indispensable for a wearable haptic glove to be truly effective. To resolve the problem of hampered motion and reach, a micro hydraulic actuating system was developed in this research. It was composed of a slim, flexible artificial muscle, a compact hydraulic module for actuating the muscle, and a micro pressure sensor for measuring without flux loss. The characteristics of the muscle were investigated for their control capacity. The step and sinusoidal responses were analyzed to evaluate the performance of the micro hydraulic system. Once these analyses were completed, a lightweight and compact actuation system was built incorporating a wearable haptic glove. By virtue of the developed micro hydraulic system, the wearable haptic glove was able to operate independently of any external equipment, and movement was completely free of any restrictions from wires or tubes.

In this paper, we present one approach to achieve safe navigation in indoor dynamic environment. So far, there have been various useful collision avoidance algorithms and path planning schemes. However, those algorithms have a fundamental limitation that the robot can avoid only "visible" obstacles. In real environment, it is not possible to detect all the dynamic obstacles around the robot. There exist a lot of "invisible" regions due to the limitation of field of view. In order to avoid possible collisions, it is desirable to consider visibility information. Then a robot can reduce the speed or modify a path. This paper proposes a safe navigation scheme to reduce the risk of collision due to unexpected dynamic obstacles. The robot's motion is controlled according to a hybrid control scheme. The possibility of collision is dually reflected to a path planning and a speed control. The proposed scheme clearly indicates the structural procedure how to model and to exploit the risk of navigation. The proposed scheme is experimentally tested in a real office building. The presented result shows that the robot moves along the safe path to obtain sufficient field of view, while appropriate speed control is carried out.

Control of a robot manipulator in contact with the environment is usually conducted by the direct feedback control system using a force-torque sensor or the indirect impedance control scheme. Although these methods have been successfully applied to many applications, simultaneous control of force and position cannot be achieved. Furthermore, collision safety has been of primary concern in recent years with emergence of service robots in direct contact with humans. To cope with such problems, redundant actuation has been used to enhance the performance of a position/force controller. In this paper, the novel design of a double actuator unit (DAU) composed of double actuators and a planetary gear train is proposed to provide the capability of simultaneous control of position and force as well as the improved collision safety. Since one actuator controls position and the other actuator modulates stiffness, DAU can control the position and stiffness simultaneously at the same joint. The torque exerted on the joint can be estimated without an expensive torque/force sensor. DAU is capable of detecting dynamic collision by monitoring the speed of the stiffness modulator. Upon detection of dynamic collision, DAU immediately reduces its joint stiffness according to the collision magnitude, thus providing the optimum collision safety. It is shown from various experiments that DAU can provide good performance of position tracking, force estimation and collision safety.

A safe robot arm can be achieved by either passive or active compliance. The passive compliance systems composed of purely mechanical elements often provide faster and more reliable responses for dynamic collision than the active ones involving sensors and actuators. Since both positioning accuracy and collision safety are important, a robot arm should exhibit very low stiffness when subjected to the collision force greater than the one causing injury to humans, but maintain very high stiffness otherwise. To implement these requirements, a novel safe link mechanism (SLM), which consists of linear springs, a double-slider mechanism and shock absorbing modules, is proposed in this research. The main contribution of SLM lies in its variable stiffness capability implemented only by passive mechanical elements. Various experiments for static and dynamic collision show that the stiffness of SLM is kept very high for the external force less than the critical impact force, but it drops abruptly as the external force exceeds the critical force, thus guaranteeing the collision safety. Furthermore, the critical impact force can be set to any value depending on the applications.

Stable haptic interaction has been studied extensively by an energy-based approach. However, the energy in the haptic system is not directly measurable, but estimated from some measured quantities such as force and velocity; therefore, the estimated energy is occasionally inaccurate. To resolve this problem, a new observer, working in the frequency domain, is proposed in this research. The observer quantifies the degree of instability of a haptic system, and a proposed controller generates variable damping in proportion to this quantitative instability. Especially, for a double layered virtual wall, the proposed methods were much faster in detecting haptic instability than other schemes, and successfully reduced unstable behavior.

Most present localization algorithms are either range or vision-based. In many environments, only one type of sensor cannot often ensure successful localization; furthermore, using low-priced range sensors instead of expensive, but accurate, laser scanners often lead to poor performance. This paper proposes an MCL-based localization method that robustly estimates the robot pose with fusion of the range information from a low-cost IR scanner and the SIFT based visual information gathered using a mono camera. With sensor fusion, the rough pose estimation from range-based sensors is compensated by the vision-based sensors and slow object recognition can be overcome by the frequent update of the range information. In order to synchronize the two sensors with different bandwidths, the encoder information gathered during object recognition is exploited. This paper also suggests a method for evaluating localization performance that is based on the normalized probability of a vision sensor model. Various experiments show that the proposed algorithm can estimate the robot pose reasonably well and can accurately evaluate the localization performance.

Accurate load sensing is increasingly important in performing various tasks involved with contacting the environment. Most research has been focused on improving the hardware of a force/torque sensor. Torque sensors for a manipulator suffer from crosstalk, which cannot be compensated even by calibration. Thus they require precise machining and complicated structure to minimize crosstalk, which often results in cost increase. This research proposes a new calibration method composed of two steps. By the primary calibration, the torque sensor output can be related to the joint torques. The secondary calibration, which is based on the virtual load, is conducted to compensate crosstalk of the torque sensor. The virtual load is obtained from the measured joint torques and the manipulator configuration. Using the proposed calibration method, the external load acting on the end-effector can be sensed accurately even with relatively low-quality torque sensors. Experimental results showed that the error in load sensing was significantly reduced by the proposed calibration method.

This paper presents mobile robot localization using coded infrared light as artificial landmarks. Different from RFID, identification using infrared light has highly deterministic characteristics. IRID(infrared identification) is implemented with IR LEDs and photo transistors. By putting several infrared LEDs on the ceiling, the floor is divided into several sectors and each sector is set to have a unique identification. The coded infrared light tells which sector the robot is in, but the size of the uncertainty is still too large if the sector size is large, which usually occur. Dead-reckoning provides the estimated robot configuration but the error is getting accumulated as the robot travels. This paper presents an algorithm which fuses both the encoder and the IRID information so that the size of the uncertainty becomes smaller. It also introduces a framework which can be used with other types of the artificial landmarks. The characteristics of the developed IRID and the proposed algorithm are verified from the experiments.

This paper proposes an energy-based control method of a haptic device with electric brakes. Unsmooth motion is frequently observed in a haptic system using brakes during a wall-following task. Since it is generally known that a haptic system using brakes is passive due to brake's characteristics, its energy behavior has seldom been investigated. However, force distribution at the end effector reveals that the unsmooth motion of a haptic system using brakes represents active behavior of the system in the specific direction. A force control scheme is proposed that computes the gain for smooth motion by considering the energy behavior of a system. Experiments show that smooth wall following is possible with a proposed force control scheme.

Exploration is the fundamental task of guiding a robot autonomously during mapping so that it covers the entire environment with its sensors. In the frontier-based exploration, a robot visits the unknown regions, but the sufficient information on the obstacles was not exploited. In the topological exploration, the robot was forced to visit all the topological nodes, but it was inefficient and time-consuming. In this paper, an efficient exploration called a thinning-based topological exploration (TTE) is proposed. This scheme is based on the position probability of the end nodes of a topological map built in real time. The robot then updates the position probability of each end node sustaining its position at the current location using the range data. By analyzing this position probability, the robot can determine whether or not it needs to visit the specific end node to examine the environment around this node. Various experiments show that the proposed TTE algorithm can perform exploration more accurately than the frontier-based exploration approach and more efficiently than the other topological exploration schemes, because in most cases, exploration for the entire environment can be completed without directly visiting everywhere

Monte Carlo localization is known to be one of the most reliable methods for pose estimation of a mobile robot. Many studies have been conducted to improve performance of MCL. Although MCL is capable of estimating the robot pose when the initial pose of a robot is not given, it takes much time for convergence because a large number of random samples are required, especially for the large-scale environment. For practical implementation of MCL, therefore, it is desirable to reduce the number of samples without affecting the localization performance. This paper presents a novel approach to reduce the number of samples used in the particle filter for efficient implementation of MCL. To this end, the topological information is extracted in real time through the thinning algorithm from the range data of a laser scanner. The topological map is first created from the given grid map of the environment. The robot scans the local environment and generates a local topological map. The robot then navigates along this local topological edge, which coincides with the global topological map obtained off-line from the given global grid map. By constraining the robot's motion on this local edge, random samples are drawn only around the neighborhood of the topological edge rather than over the entire free space. Hence the sample size required for MCL can be drastically reduced, thereby reducing computational time for the MCL process. A series of experiments based on this proposed MCL/TI show that the number of samples can be reduced considerably, and thus the time required for pose estimation can be substantially decreased

This paper presents a wearable haptic system to interact with virtual environment. The proposed haptic system makes a user interact intuitively with virtual environment, while the user moves freely around the environment. To make wearable system, the light-weight and compactness are emphasized during the design process. MR(magneto-rheological) brakes are adopted as actuators for the device, because a brake (passive actuator) has much larger value of a relative torque/weight ratio than a motor (active actuator). As a result a new wearable haptic system, which is folded to compact size and has large workspace, is developed. To evaluate the proposed system, tangible studio is implemented to experience a virtual heritage alive

This paper proposes a control method that overcomes the instability arising from both the low update rates of the virtual environment (VE) and the time delay in a communication line. The instability arising from the time delay in a communication line can be overcome using the wave variables since time delay on the wave variables is passive. The so-called multirate control scheme is applied to cope with the problems presented by the low update rates of VE. Since digital sample and hold (rate transitions) can be represented as a series of time delay, the passive nature of time delay on the wave variables is applied. By computing the norm of the scattering matrix, it was verified that rate transitions on the wave variables are passive, thereby deriving a stable haptic interface with the multirate wave transform. Various experiments have shown that a stable force display is achieved with the multirate wave transform.

It is well known that the wave variables are robust to time delay of a system from the viewpoint of passivity. During implementation of the wave transformation on the sampled-data system, a unit time delay arises due to causality of the reflection wave. The unit time delay on the reflection wave occasionally becomes a passive element. From the passivity condition of the sampled-data system, the wave impedance can be designed such that the wave transformation using delayed reflection provides the effect of positive damping and thus the stable haptic interface is achieved on the sampled-data system. Various experiments for a 2-linked passive haptic device show that stable haptic interface can be accomplished for the wall-following task by use of the wave transformation using delayed reflection.

Wave variables have been used to overcome the transmission delay of a system from the viewpoint of passivity. During implementation of the wave transformation for the sampled-data system, a unit delay arises due to causality of the reflection wave. The property of the wave transformation using delayed reflection, which is different from the standard wave transformation, can be verified with the passivity condition of the scattering matrix. The unit delay on the reflection wave occasionally becomes a positive damping. From the passivity condition of the sampled-data system, the wave impedance can be designed such that the wave transformation using delayed reflection wave provides the effect of positive damping. As an example, the wave transformation using delayed reflection wave makes it possible that the stable haptic interface is achieved on the sampled-data system with appropriate wave impedance. The simulation and the experiment results show that the stable haptic interface can be accomplished by use of the wave transformation using delayed reflection.

We propose an energy-based control method of a passive haptic device equipped with electric brakes. Unstable behavior is observed in the passive haptic system due to time delay mainly arising from the slow update rate of the virtual environment. From the passive FME (force manipulability ellipsoid) analysis, a so-called direct force control method is proposed in this paper. Its gain is computed by force analysis at the end-effector of a passive haptic device so that the component of a resultant force at the end-effector causing a pullback motion becomes zero. However, this direct force control scheme requires precise measurement of the hand force input by a human operator. We also propose the indirect force control scheme in which the gain in the direct force control scheme is computed using the notion of passivity without resorting to the high precision force sensor. For the experiments a 2-link passive haptic system was developed in this research. Various experiments have been conducted to investigate the validity of both direct and indirect force control schemes proposed in this paper. It is shown that both schemes produce satisfactory performance in the force display for the wall-following task on the virtual wall.

Open-loop estimation methods are commonly used in mobile robot applications. Their strength lies in the speed and simplicity of an estimate. However, these methods can sometimes lead to inaccurate or unreliable positional estimates. Using one or more optical flow sensors, a method has been developed which can accurately track position in both ideal kinematic conditions and otherwise. Using optical flow techniques and available sensors, reliable positional estimates are made. The sensor provides accurate measurement of the movement at the sensor location. Even though the sensor does not provide angular displacement, the robot movement is estimated using only one sensor even with wheel slip. However, when the robot moves sideways due to external disturbance, redundant sensors are used in order to estimate the configuration of the robot. Pseudo inverse based estimation and the extended Kalman filter based estimation are presented to show the effectiveness of the proposed approach. Location of the sensors has also been investigated in order to minimize errors caused by inaccurate sensor readings. Finally, the method is implemented and tested using a potential field based navigation scheme.

A mobile service robot can achieve reconfigurability by exploiting passive trailer systems. Reconfigurability provides significant practical advantages in order to deal with various service tasks. However, a motion control problem of a passive multiple trailer system is difficult, mainly because a kinematic model is highly nonlinear. It is shown how a robot with n passive trailers can be controlled in backward direction. Once a desired trajectory of a last trailer is computed, then the control input of a pushing robot is obtained by the proposed control scheme. A kinematic design of a trailer system is proposed in our prior work. It is shown that the high performance of trajectory tracking is also valid for the backward motion control problem. Experimental verifications were carried out with the PSR-2 (public service robot) with three passive trailers. Experimental result showed that the backward motion control could be successfully carried out using the proposed control scheme.

An accurate and compact map is essential to an autonomous mobile robot system. A topological map represents the environment in terms of the discrete nodes with edges connecting them. It is usually constructed by the Voronoi-like graphs. In this paper the topological map is incrementally built based on the local grid map using the thinning algorithm. This thinning-based topological map does not create the boundary edges and weak meet points which are found in the generalized Voronoi graph. Furthermore, the map can be built in real-time and is robust to the environment change. Since lack of metric data in the topological map poses difficulty in localization, the metric features such as corners are incorporated into the topological map, thus leading to the hybrid map. In this paper the detailed procedure to obtain this hybrid map is discussed and the experimental results are shown to verify the validity of the proposed algorithm

This paper describes a multi-modal interface design and its implementation to a teleoperated field robot system. The ROBHAZ-DT2 is developed as a teleoperated mobile manipulator for hazard environment applications (e.g. rescue, explosive ordnance disposal, security). To complete these missions in outdoor environment, the robot system must have appropriate functions, accuracy and reliability. However, the more functions it has, the more difficulties for the operator to control the functions. To cope up with this problem, an effective user interface should be developed. The main challenge of this research is to make a simple and intuitive user interface and teleoperate the slave robot easily. This paper provides multi-modalities such as visual, auditory and haptic sense. It enables an operator to control every functions of a field robot, ROBHAZ-DT2 more easily. In this paper, an EOD (explosive ordinance disposal) demonstration is conducted to verify the validity of the proposed multimodal interface.

In a previous research, a new class of an omnidirectional mobile robot was proposed. Since it has synchronously steerable omnidirectional wheels, it is called an omnidirectional mobile robot with steerable omnidirectional wheels (OMR-SOW). It has 3 DOFs in motion and one DOF in steering. One steering DOF can function as a continuously variable transmission (CVT). CVT of the OMR-SOW increases the range of velocity ratio from the wheel velocities to robot velocity, which may improve performance of a mobile robot. In this paper, kinematics and dynamics of this robot are analyzed. A control algorithm for CVT mounted on the OMR-SOW, which considered motor efficiency in its operation, is discussed in detail. Various tests have been conducted to demonstrate validity and feasibility of the proposed mechanism and the steering algorithm. Experimental results show the OMR-SOW can be driven more efficiently with the proposed steering algorithm and a CVT mechanism.

This paper presents design of a 6 DOF haptic master which is based on a combination of a planar 3 DOF parallel mechanism and a spatial 3 DOF parallel mechanism. Since low inertia is vital to backdrivability and transparency of the haptic device, all actuators are placed on the base and thus some forces for haptic feedback are transmitted by tendon-driven mechanism. This device was intended to teleoperate a mobile manipulator, which requires planar 3 DOF motion for navigation of the vehicle and full 6 DOF motion for manipulation. Therefore, the proposed device is designed to have two modes of a planar task and a 3D task which are switchable without any change in hardware. This feature provides efficient actuation and reduces computational burden since only 3 actuators are involved in the case of a planar task. The paper deals with a detailed description of the proposed haptic master and Jacobian analysis. Some applications are given to verify the validity of this device.

In this paper, a new design of a 6DOF haptic master is presented, and the architectural parameters are discussed in consideration of the kinematic characteristics. This device was intended to teleoperate a mobile manipulator, which requires planar 3 DOF motion for navigation of the vehicle and full 6 DOF motion for manipulation. The proposed haptic master is composed of two parallel mechanisms, and each mechanism offers 3 DOF independently. The spatial mechanism, which extends the workspace into 3D, is attached on the planar mechanism for vehicle operation. Since low inertia is vital to back-drivability and transparency of the haptic device, ail actuators are placed on the base and thus some forces for haptic feedback are transmitted by the tendon-driven mechanism. This paper presents the kinematic analysis of the haptic master with respect to the workspace and the performance indices related to the Jacobian. The actual system was constructed with the architectural parameters determined on the basis of the analysis.

An omnidirectional mobile robot equipped with four independent omnidirectional wheels can perform 3 DOF motion and has one redundant DOF. This redundancy can be used to drive the mechanism enabling the wheel arrangement to vary, which can function as a continuously-variable transmission (CVT). In this research, a special mechanism called a variable wheel arrangement mechanism is proposed to increase the range of velocity ratio for the CVT from the wheel velocities to robot velocity, which may improve performance of the mobile robot. A mobile robot with this mechanism was constructed and various tests have been conducted to demonstrate the validity and feasibility of the proposed mechanism.

Kinematic and dynamic characteristics of Stewart platform based parallel manipulators are fixed once they are constructed. Thus parallel manipulators with various configurations are required to meet a variety of applications. In this research a variable arm type parallel manipulator (VAPM) was developed, in which the length of the arm linking the platform center to the platform-leg contact point can be varied by the actuator. Workspace of the VAPM is larger than that of a traditional Stewart platform and especially the range in which the maximum orientation angles can be maintained is significantly expanded. Furthermore, the characteristics of force and moment transmission between the legs and platform can be adjusted to meet the requirements of various tasks. Kinematic and dynamic analysis was performed to verify the usefulness of the VAPM and the actual hardware was built to demonstrate the feasibility.

Map building and localization are essential to an autonomous mobile robot system. A global topological map is commonly constructed from a global grid map using a Voronoi diagram. In this hierarchical method, however, the advantage of a topological map such as compactness may not be fully utilized. In this paper sensor data are used to build a local grid map from which a local topological map is created using a thinning method. The thinning method is an alternative of the Voronoi diagram. The local topological map is then updated to the global one. Localization based on the topological map is usually difficult, but additional nodes created by the thinning method can improve localization performance. Various experiments with a laser scanner demonstrate validity and feasibility of the proposed algorithms for map building and localization.

Most omnidirectional wheels with passive rollers have a gap between rollers. This gap causes the wheel to make discontinuous contact with the ground, and leads to vertical and/or horizontal vibrations. In this paper a novel design of continuous alternate wheel is proposed to minimize a gap between rollers. In the continuous alternate wheel, inner and outer rollers are arranged continuously, thus resulting in no gap between the rollers. This paper details the design process including the systematic approaches to determine the optimum number of rollers, the radii of rollers and the inclination angle of the inside of an outer roller for given design specifications. Finally, an actual continuous alternate wheel is constructed to verify validity of the design guidelines.

A new wheel assembly automation system is proposed which assembles a wheel into a hub on a car body on a moving hanger in the car manufacturing line. A vision system is used to track the position of the hub on the moving hanger A macro-micro structure is applied to increase a system bandwidth and accuracy to meet an insertion tolerance. The redundancy problem is solved without complicated calculations by assigning different functions that the macro manipulator tracks a velocity error and the micro regulates the position error. Experimental results show that the proposed system can be applied to the wheel assembly task on a moving hanger in the car manufacturing line.

Configuration-dependent nonlinear coefficient matrices in the dynamic equation of a robot manipulator impose computational burden in real-time implementation of tracking control based on the inverse dynamics controller. However, parallel manipulators such as a Stewart platform have relatively small workspace compared to serial manipulators. Based on the characteristics of small motion range, nonlinear coefficient matrices can be approximated to constant ones. The modeling errors caused by such approximation are compensated for by an H-infinity controller that treats the error as disturbance. The proposed inverse dynamics controller with approximate dynamics combined with H-infinity control shows good tracking performance even for fast tracking control in which computation of full dynamics is not easy to implement.

The human response caused by the motion of an object grasped by a human operator is defined as an arm kinesthetic sense. Due to nonlinearity and ambiguity of human senses, there is no absolute standard for quantification of kinesthetic sense. In this research, a so-called two-dimensional (2-D) arm motion generator is developed to emulate various mechanical impedance, i.e., stiffness or damping, characteristics of a human arm. The words representing arm kinesthetic sense are selected and then the subject's satisfaction levels on these words for given impedance values are measured and processed by the semantic differential method and factor analysis. In addition, in order to reflect the individual differences of each subject in the arm kinesthetic sense, compensation for individual differences based on the neural network technique is proposed. Through this proposed algorithm, the human sensations to arm movements described qualitatively can be converted into engineering data ensuring objectivity, reproducibility, and universality. This database can be used to develop user-friendly products related to arm motion.

Regrasping, given initial and final pose of the target object, is a construction of sequential transition of object poses that are compatible with two poses in the point of grasp configuration. This paper presents a novel approach for solving the regrasp problem. The approach consists of a preprocessing and planning stages. Preprocessing, which is done only once for a given robot, generates a look-up table which has information of kinematically feasible task space of end-effector through all the workspace. Then, using the table, planning automatically determines possible intermediate location, pose and regrasp sequence leading from the pick-up to put-down grasp. Experiments show that the approach presented is complete in the total workspace. The regrasp planner was combined with the existing path.

A two-arm cooperative assembly (or insertion) algorithm is proposed. As a force-guided control method for the cooperative assembly, the adaptive accommodation controller is adopted since it does not need any complicated contact state analysis nor depends on the geometrical complexity of the assembly parts. Also, the RMRC (resolved motion rate control) method using a relative Jacobian is used to solve inverse kinematics for two manipulators. By using the relative Jacobian, the two cooperative redundant manipulators can be structured as a new single redundant manipulator. The two arms can perform a variety of insertion task by a relative motion between their end effectors. A force/torque sensing model, using an approximated penetration depth calculation algorithm is developed and used to compute a contact force/torque in the graphic assembly simulation. By using the adaptive accommodation controller and the force/torque sensing model, a spatial cooperative assembly tasks have been successfully executed in the graphic simulation. Finally, through a cooperative assembly task experiment using a humanoid robot, CENTAUR, which inserts a spatially bent pin into a hole, its feasibility and applicability are verified.

In remote control systems, it is crucial to increase the work efficiency by providing the real situation to an operator in simulated way through the delivery of force and vision data. In this research, the physical parameters of a master are to be rearranged on the basis of the operator and combined into impedance control system to offer the operator the experience of the rearranged sensibility. To carry out this task, statistical factor analysis of human senses and extraction of proper sensibility ergonomics words were executed by quantification of senses on the basis of sensibility ergonomics theory To display the desired sense to an operator in real time, sensibility ergonomics database and sense interface operating in the Windows environment were constructed.

To increase the accuracy and the reliability of teleoperation, close interaction between human and the slave robot is required. Korea Institute of Science and Technology (KIST) is developing a Humanoid robot, which has two 9-DOF arms, two 4-DOF hands, a 3-DOF waist and a 2-DOF neck. An automatic path planner which takes advantage of redundancy is also developed, but it requires huge computational power and time. For tasks which are very complex, or interacting with environments, robot path can be generated very easily and accurately by human teaching, hence the automatic path planner is not required. Using sensors, human motion is analyzed and converted to robot joint angles. For tasks interacting with unknown environment, teleoperation with force feedback is more useful. A simple platform-type master arm is designed based on the kinematic analysis of human. For force reflection, the pneumatic actuators are used. This device is integrated with KIST Humanoid robot as well as graphic simulator, so that the master arm can be used for teaching the robot or as the virtual reality device integrated with the graphic simulator. Force reflecting master hand is also developed. These force reflecting master arm and hand are very light and compact so that a human can wear easily while he feels the same force as the robot does while giving position command to the slave robot. In addition to master arm/hand, visual information is feedback to human through HMD for higher interaction. Therefore, a new way of integration of human and the robot is developed.

A lot of research has been done in robot path generation, including automatic path planning and teaching/playback. Teleoperation is commonly used to control a robot from a remote site in an unknown environment. Korea Institute of Science and Technology (KIST) is developing a Humanoid robot, which has two arms (9 degrees of freedom for each), two hands (4 d.o.f. each), a waist (3 d.o.f.) and a neck (2 d.o.f.) An automatic path planner which takes advantage of redundancy is also developed, however, it requires huge computational power and time. For some tasks, which are very complex, or interacting with environments, the robot path can be generated very easily and accurately by human teaching, hence the automatic path planner is not required. Using sensors, human motion is analyzed and converted to robot joint angles. For tasks interacting with an unknown environment, teleoperation with force feedback is more useful. A simple exoskeleton-type master arm is designed based on kinematic analysis. For force reflection, pneumatic actuators are used. This device is integrated with KIST Humanoid robots. A force reflecting master hand is also developed. In addition to the master arm/hand, visual information is fed back to the human through HMD for higher interaction, and voice command interpreter/voice synthesis is integrated. Therefore a new method of human/robot integration is developed.