Multi-DoFs (Degrees of Freedom) manipulators with more than 6-DoF can perform complex and diverse tasks. To make these serial-chain manipulators safer, a variety of safety components were researched. If there is a crash at the end-effector of the serial-chain manipulators, components mounted on joints of the upper and lower arm can absorb the impact. Unfortunately, physical human-robot interaction does not occur only at the end-effector, a collision can happen anywhere from the base to the end-effector. If a collision occurs in the upper arm of relatively low DoFs, safety components attached to each joint may not work properly. Therefore, a study for joint configurations of serial manipulators is necessary with respect to the placement of safety components at the shoulder joint. Through various case studies, this paper verifies the appropriate joint configurations that place safety components at each revolute joint for physical human-robot safety.

We propose a design method for a gravity compensator using unit spring balancers for multi-degree-of-freedom (DOF) and multilink manipulators. Existing spring balancers can be applied to a new design of a gravity compensator. When applying spring balancers to a new gravity compensator, it is necessary to determine how many spring balancers are required and where they should be placed. Our proposed design method can determine the number of spring balancers and their locations. In this study, the design of a spring balancer for multi-DOF and multilink manipulators is considered as a mapping between two spaces (i.e., the joint space for gravitational torques and the spring balancer space to compensate torques). The mapping matrix is obtained through eigenvalue analyses of the potential energy function. The number of rows of the mapping matrix represents the number of unit gravity compensators. The row vector of the mapping matrix also indicates the locations of the unit gravity compensators. Examples are presented to validate the effectiveness of the proposed method.

This paper proposes a design method of a static balancing mechanism using unit gravity compensators (e.g., 1-dof gravity compensator). In the design of a multi-dofs static balancing mechanism it is necessary to determine how many springs (or unit gravity compensators) are required and where they should be placed. This problem can be overcome by computing the mapping matrix between the joint space and gravity compensator space. The mapping matrix is obtained by analyses of the potential energy function. The number of rows of the mapping matrix indicates the amount of unit gravity compensators and linear joint constraints representing locations of unit gravity compensators. Example studies are presented to verify the effectiveness of the proposed method. Simulations are performed in that static balancing mechanisms designed by the proposed method can counterbalance the gravitational torques completely.

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.

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.

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.

In this paper, we propose an energy-based stability control of a passive haptic device equipped with passive actuators such as an electric brake. Unstable behavior is observed even in the passive haptic system due to time delay mainly arising from the slow update rate of the virtual environment. The force approximation, one of the major limitations of the passive haptic device, is explained in the passive FME analysis. The ideal force display of passive haptic device is investigated, and it is shown that the passive haptic system frequently obtains the pullback capability due to the force approximation. The indirect force control scheme is proposed in that the change rate of passivity is controlled to simulate the ideal force display. To avoid the increase of the passivity due to the rate controller, which is not correlative to stability, passivity feedback is established. An experiment was conducted with a 2-link passive haptic device equipped with two electric brakes. From the experiment, the proposed control method showed satisfactory performance in displaying a plain virtual wall.

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.

The design and integration of ROBHAZ-DT2 is presented which is a newly developed mobile manipulator system. It is designed to carry out military and civilian missions in various hazardous environments. In developing the integrated ROBHAZ-DT2 system, we have focused on two issues: 1) novel mechanism design for mobility and manipulation and 2) intuitive user interface for teleoperation. In mechanism design, a double tracks connected by a passive joint has been designed to achieve high speed and rugged mobility on uneven terrain. In addition, a six-dof foldable manipulator suitable for the mobile manipulation has been designed. Secondly, a new compact 6-dof haptic device has been developed for teleoperation of the ROBHAZ-DT2. This haptic device is specially designed for simultaneous control both of the mobile base and the manipulator of ROBHAZ-DT2. As a result of integration of ROBHAZ-DT2 and the user interface unit including the haptic device, we could successfully demonstrate a typical EOD task requiring abilities of mobility and manipulation in outdoor environment.

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.

A new concept of the exoskeleton-type masterarm, composed of serial links, is introduced in the paper. To provide maximum range of human motion, several redundant joints are added to the serial links. In order to reduce the number of joints to be measured, kinematics of serial links was taken into consideration in design. Three measurable, controllable joints and three redundant free joints are used for the upper arm (shoulder), similarly to the forearm (wrist) while one measurable, controllable joint is used for the elbow. In particular, a torque sensor beam is designed for fine force reflection using the strain gauge. It detects the torque as well as its direction applied by the human operator, which allows the electric brake to be used as an actuator for force reflection. The electric brake constrains the joint movement so that the operator can feel the force. This electric brake outperforms the motor in terms of torque/weight ratio and makes the device light and compact. This masterarm measures the movement of the operator's arm precisely, and its can be used for teleoperation with a slave robot, or as a motion planner for an industrial robot.

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.