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 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.

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.

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.

A framework is defined as a set of reusable designs of all or part of a software system described by set of abstract classes and the way in which instances of those classes collaborate. It is intended to capture the functionality that is common to several similar applications. By developing and reusing frameworks, the reuse also encompasses design and analysis. When programmers develop applications in a specific domain using a RAD (rapid application development) tool with which frameworks are provided, they can focus their attention on their particular problem domain and do not have to start from scratch each time they write applications. In this paper, we design and implement a framework diagram and a framework-based RAD tool, called INTRAD (INTranet RAD). Also, we implement an e-mail framework for the INTRAD system, which supports the development of intranet applications.