materials handling industry has developed a great variety of so-called "assist devices" that provide support against gravity and sometimes guide motion but do so at the expense of much greater inertia, anisotropic response to the operator's applied forces, restriction of motion to few dimensions, and greater possibilities of jamming in assembly operations. Thus, conventional assist devices usually reduce productivity. Their clunkiness frustrates operators, often leading to disuse in practice. Damaging collisions may occur, reducing productivity.

Virtual surfaces, whether enforced by a cobot or a conventionally actuated robot, can solve many of the problems of assist devices, if they can be implemented on an appropriately large scale of workspace size and strength. However, the force magnitudes needed are almost by definition at least those of humans. The speeds, if we are to increase rather than decrease productivity, must be at least those of humans. This would seem to imply a need for large motors with greater-than-human power. Workers are understandably leery of such motors in the context of a general-purpose manipulator, if they are intended to work within its workspace.

Cobots, in contrast, rely on the worker to provide motive power or can give some small powered assistance that requires only small motors. The much greater need for force is that required for changes of direction, sometimes called "inertia management." In cobots this is accomplished by the physical mechanism of the cobot rather than by motors, with a consequent improvement in both safety and smoothness of operation.

Space permits only the briefest explanation of the mechanism of cobots. The simplest cobot has a two-dimensional (planar) workspace and a mechanical heart that is a single wheel (see Figure 1). Most interest lies in extension of the cobot idea to many dimensions of motion and to revolute joints. The latter uses a continuously variable transmission in place of a wheel. Interested readers are referred to http://cobot.com for further information.

The motor in Figure 1 simply steers the wheel. No amount of malevolent steering by the control computer can cause the cobot to move on its own. Only the operator can cause it to move, by applying forces to the handle. A force sensor (top) monitors these user forces.

The unicycle cobot displays two essential behaviors: free mode and virtual surface. Free mode is invoked when the cobot's position in its planar workspace is away from all defined constraint surfaces. The cobot should therefore permit any motion the user attempts to impart. To do this, the steering angle of the wheel is servocontrolled such that user forces perpendicular to the wheel's rolling direction are nulled. The behavior is similar to that of a caster wheel on a rolling item of furniture, although there is no physical caster at all.

When the user brings the cobot's position in the plane to a place where a constraint surface is defined, control of the steering angle changes over to virtual surface mode. The wheel is steered such that its rolling direction becomes tangent to the constraint surface, and this tangency is maintained as the user moves

Front Matter (R1-R12)

Biomaterials and Optical Imaging for Biomedicine (1-34)

Advanced Materials (35-62)

Simulation in Manufacturing (63-84)

Robotics (85-110)

Dinner Speech (111-122)

Contributors (123-130)

Program (131-134)

Participants (135-144)

Glossary (145-146)