Changhyun Cho

ROBHAZ-DT2: design and integration of passive double tracked mobile manipulator system for explosive ordnance disposal

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.

Static balancing of a manipulator with hemispherical work space

This paper proposes a gravity compensator for the roll-pitch rotation which can be operated in hemispherical work space. The gravity compensator comprises two 1-dof gravity compensators and a bevel differential. It is revealed from analyses of energy and torque that the proposed gravity compensator can perform static balancing completely. The gravity compensation of a 4-dofs manipulator is briefly introduced for example. Experiments show that the proposed compensator can counterbalance the gravitational torques effectively and can be operated in hemispherical work space.

Design of a Static Balancing Mechanism for a Serial Manipulator With an Unconstrained Joint Space Using One-DOF Gravity Compensators

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.

Stable Haptic Display of Slowly Updated Virtual Environment With Multirate Wave Transform

This paper proposes a control method that overcomes the instability of a haptic interface arising from both the slow 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 the time delay on the wave variables becomes passive. The so- called multirate control scheme is applied to cope with the problems presented by the slow update rates of the 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 become passive, so a stable haptic interface was derived with the multirate wave transform. Various experiments have shown that a stable force display can be achieved with the multirate wave transform.

Performance analysis of a 2-link haptic device with electric brakes

Passive haptic devices have better stability than active ones, but usually have limited capability of haptic display. In this paper a 2-link passive haptic device equipped with electric brakes is discussed. Since passive devices cannot generate forces in all directions, determination of the region available for force reflection is important to their design and operation. This analysis can be done by a so-called force manipulability ellipsoid (FME). In some haptic applications, the endpoint of a device is required to move along a certain trajectory (e.g., the surface of a virtual wall) and haptic display plays a role of path guide. Performance of path guidance is also investigated in this research. Finally, guideline for the design of more efficient passive haptic devices is briefly discussed.

Integration of Hall and Giant Magnetoresistive Sensor Arrays for Real-Time 2-D Visualization of Magnetic Field Vectors

In this study, we combined an array of giant magnetoresistive (GMR) sensors with an array of Hall sensors to measure all three components of magnetic vectors with a high spatial resolution and visualize the magnetic field distribution on a 2-D plane. The sensors were arrayed in a matrix arrangement such that the limitation to the number of sensors could be overcome. To test the device, we generated a magnetic field using a pancake-type magnetizer and a cracked magnetized ferromagnetic specimen and imaged the vectors. We obtained a spatial resolution of 0.78 mm in the z-direction with 1024 Hall sensors and 2.34 mm in the x-direction with 100 GMR sensors. Moreover, the x and z components could be imaged at 6 fps. The proposed device is promising for application in magnetic flux leakage detection.

Energy-Based Control of a Haptic Device Using Brakes

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 brakes 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

Design of a static balancing mechanism with unit gravity compensators

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.

A new exoskeleton-type masterarm with force reflection based on the torque sensor beam

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 operators arm precisely, and its can be used for teleoperation with a slave robot, or as a motion planner for an industrial robot.

Stable Haptic Display of Slowly Updated Virtual Environment with Multirate Wave Transform

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.