Legged robots have high mobility for application with uneven terrain. Bipedal robots require the lower number of actuators with less complication of control system, but their walking stability is the main challenge. This paper presents a design of the bipedal robot having two actuated joints for the hip and the knee and one passive joint for the ankle of each leg. To minimize the inertia of the moving legs, the four brushless motors with integrated controller and planetary gearbox are concentrically located at the hip axis while the knee joints are driven through the parallel linkages. The zero-moment point (ZMP) along the foot support contacting the floor was derived based on the table-cart model. During the stance phase of stable walking, the desired ZMP must be located within the foot boundary. The ZMP generator for shifting the center of mass (COM) forward according to the stride was simulated along with kinematics of the legs. The hip and the knee joint trajectories were implemented on the bipedal robot prototype. The desired leg kinematics was validated by the experiment. As the load supported by the feet, the effect of gravity on the leg joint positions and torques was also studied. Additional sensing and the control of joint stiffnesses will be applied for achieving the dynamic walking of the bipedal robot.

Manipulating mechanical energy intelligently, passive exoskeletons can improve the energy efficiency of cyclic human motions. Aiming to reduce the energy cost of knee moment during stair ascent, this paper presents a concept of brake-torque support activated when the knee moment is required in the opposite direction to the angular velocity of the knee joint. Integrating an electromagnetic brake to a crossing four-bar knee joint with a compact design, the passive knee exoskeleton enables the polycentric knee center of rotation covering the wide range of knee angle during stair ascent. For preliminary validation, the surface electromyography (EMG) of rectus femoris (RF) and biceps femoris (BF) were studied on a healthy male volunteer wearing the exoskeleton on his right leg. The reduction of peak muscle activity is observed as the brake torque is applied during knee extension while the knee flexion moment is required.

We describe a new robot architecture: the collaborative robot, or cobot. Cobots are intended for direct physical interaction with a human operator. The cobot can create smooth, strong virtual surfaces and other haptic effects within a shared human/cobot workspace. The kinematic properties of cobots differ markedly from those of robots. Most significantly, cobots have only one mechanical degree of freedom, regardless of their taskspace dimensionality. The instantaneous direction of motion associated with this single degree of freedom is actively servo-controlled, or steered, within the higher dimensional taskspace. This paper explains the kinematics of cobots and the continuously variable transmissions (CVT) that are essential to them. Powered cobots are introduced, made possible by a parallel interconnection of the CVT. We discuss the relation of cobots to conventionally actuated robots and to nonholonomic robots. Several cobots in design, prototype, or industrial testbed settings illustrate the concepts discussed.

Intelligent assist devices (IADs) are a new class of hybrid devices for direct, physical, interaction with a human operator in shared workspaces. These devices-designed for the assembly line worker-can reduce ergonomics concerns that arise due to on-the-job physical and cognitive loading, while improving safety, quality and productivity. Cobots, a sub-set of IADs, implement software defined virtual guiding surfaces while providing some amplification of human power. They exemplify the central theme of this paper-that humans are critical in many assembly operations and ergonomics tools that enable them to perform their duties are necessary. The paper describes broad design principles for human-machine interaction in these industrial settings. Prototype industrial cobots designed for testing and validation are described.

Cobots are a class of mechanically passive robotic devices, intended for direct physical collaboration with a human operator. The operator supplies all motive power while the cobot enforces software-defined guiding surfaces, or constraints. Cobots are intrinsically passive, safe devices. This is because, rather than employ powered actuators to produce constraint forces, cobots use "steerable" nonholonomic joints. Constraint forces are mechanical in origin, yet software defined. The simplest possible cobot is a unicycle which is steered by a servo system acting under computer control, but which is moved by a human operator. The unicycle cobot requires essentially no consideration of kinematics. Two fundamental control modes of the unicycle cobot, "virtual caster" and "constraint tracking", are reviewed. More complicated cobots, such as the three-wheeled "Scooter", require a set of kinematic tranformations relating configuration space to joint space. These transformations play a role in cobot control like that of the Jacobian in robot control.

Conventional approaches to haptic interface rely on high gain servos to implement virtual constraints. The role of the servo is to reduce the apparent degrees of freedom in such a way as to effectively constrain a human operator's motion. A significant drawback of this approach, however, is that the operator must interact directly with a high power system that is not inherently passive, and which may become unstable. In this paper, we present a novel approach to haptic display which allows virtual constraints to be implemented in a manner that is completely passive and therefore intrinsically safe. The key idea is to begin with a device having zero or one degree of freedom, and to use feedback control to increase the apparent degrees of freedom as necessary. This becomes possible with the use of nonholonomic joints, which have fewer degrees of freedom than generalized coordinates. The design and feedback control of several "programmable constraint machines" (PCMs) of this type are discussed.