Anthropomorphic arm manipulators usually consist of as a series of revolute joints and links. In this paper, serial-chain manipulators are described by a novel kinematic representation using a series of type R or T joints, which are classified according to relation between a rotational axis and two adjacent links. It provides an easy intuition to describe general types among existing manipulators and also to get intuitive ideas before designing of joint and link modules of modular manipulators. From these intuitive idea about joint configurations using two types of joints, a new concept of joint module with two input and one output connections is presented. This joint module enables to couple directly between two joint modules. In addition, practical solutions of mechanical and electrical connections between joint or link modules is introduced. The connection can be established between two modules via eight types of relative positions of 45 degree intervals. Using joint and link modules, 3-DoF(Degrees-of-Freedom) modular manipulators of three kinds of joint configurations are shown representatively. After assembly, the standard D-H(Denavit-Hartenberg) parameters of three examples are obtained utilizing information of joint and link modules.

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.

Interaction with humans is inevitable for service robots, which results in safety being one of the most important factors in designing the robots. Compliant component is an answer to the safety issue at the cost of performance degradation. In order to reduce the performance degradation, manipulators equipped with variable stiffness have been studied by many researchers. This paper presents a variable stiffness joint (VSJ) designed for a robot manipulator, as well as a control scheme to control the stiffness and position of the VSJ. Compliance is generated by leaf springs and two actuators are used to control the position and stiffness of the joint using four-bar linkages. Two actuators in parallel configuration are connected to the spring. Changing the effective length of the spring results in a change in stiffness. The position of the joint is controlled via two actuators rotating at the same speed in the same direction. A nonlinear controller is used to control the VSJ, and a singular perturbation model is adopted to prove the stability of the closed-loop system. Experiments are conducted to show that the position and stiffness are controlled independent of each other, and having less stiffness at the joint helps in making an unexpected collision with an object safer.

Safety of a manipulator designed to be used at home requires different approach than industrial robots, where safety is achieved mainly by decreasing the interaction with humans. Robots for applications at home, however, require frequent interaction with humans. Introducing compliant component gives the answer to the safety issue at the cost of performance degradation. In order to reduce the performance degradation, manipulators equipped with variable stiffness have been studied by many researchers. This paper presents a variable stiffness joint(VSJ) designed for a robot manipulator. The stiffness is generated by leaf springs and two actuators are used to control the position and stiffness of the joint. Changing the effective length of the spring results in change in stiffness. The position of the joint is controlled via rotating two actuators at the same speed in the same direction. The stiffness is controlled when the two actuators rotate in the different speed. Experiments are conducted to show that the position and stiffness are controlled independent with each other and having less stiffness at the joint helps in making unexpected collision with object safer.