Stephen C. Jacobsen

The UTAH/M.I.T. Dextrous hand: work in progress

The Center for Biomedical Design at the University of Utah and the Artificial Intelligence Laboratory at the Massachu setts Institute of Technology are developing a tendon-oper ated multiple-degree-of-freedom dextrous hand (DH) with multichannel touch-sensing capability. Our goal is the design and fabrication of a high-performance yet well-behaved sys tem that is fast and stable and that includes considerable operational flexibility as a research tool. The paper reviews progress to date on project subtasks and discusses design issues important to hardware and control systems develop ment in terms of (1) structures that contain tendons, actua tors, joints, and sensors; (2) both pneumatic and electric tendon actuation systems; (3) optically based sensors that detect touch; (4) subcontrol systems that provide internal management of the DH; and (5) preliminary higher control systems that supervise general operation of the hand during execution of tasks and that provide integration of vision and tactile information.

CB : a humanoid research platform for exploring neuroscience

This paper presents a 50-d.o.f. humanoid robot, Computational Brain (CB). CB is a humanoid robot created for exploring the underlying processing of the human brain while dealing with the real world. We place our investigations within real—world contexts, as humans do. In so doing, we focus on utilizing a system that is closer to humans—in sensing, kinematics configuration and performance. We present the real-time network-based architecture for the control of all 50 d.o.f. The controller provides full position/velocity/force sensing and control at 1 kHz, allowing us the flexibility in deriving various forms of control. A dynamic simulator is also presented; the simulator acts as a realistic testbed for our controllers and acts as a common interface to our humanoid robots. A contact model developed to allow better validation of our controllers prior to final testing on the physical robot is also presented. Three aspects of the system are highlighted in this paper: (i) physical power for walking, (ii) full-body compliant control—physical interactions and (iii) perception and control—visual ocular-motor responses.

Quantitation of human shoulder anatomy for prosthetic arm control-I. Surface modelling

Anatomical data and models for the human shoulder musculo-skeletal system are developed with the intent of quantifying physiological subcomponents of a model-based multi-axis prosthetic limb control scheme which has heretofore been implemented empirically. Part I presents the controller formulation, the surface descriptions of the muscles (and bones), and the centroidal trajectory data of the muscles. The data partially quantify the muscle modelling components of the controller, and set the stage for the analysis of the force-to-moment anatomical conversion factors of Part II.

A design overview of an eccentric-motion electrostatic microactuator (the wobble motor)

Abstract A description is given of the design, fabrication and analysis of an electrostatically-driven micro-actuator in which a planetary-motion rotor rolls inside a cylindrically shaped stator cavity. The design has four primary advantages: (1) the motor geometry and the rolling motion enable very small gaps to be achieved, which are accurate and stable, and across which electrostatic forces act, leading to high forces on the rotor; (2) relative motion is achieved by rolling rather than sliding, thus obviating the concern over internal friction; (3) higher output torques can be traded for lower rotor speeds, due to immediate planetary reduction; and (4) the power output should be higher than for systems constructed using two-dimensional silicon fabrication approaches, since woble motor lengths are not limited by such fabrication methods. The stator segment recruitment logic can range from simple, open-loop stepping to full servo-controlled commutation using rotor position sensors. Two-dimensional analytical and finite-element simulations that estimate motor torque generated by electrostatic fields have been used to determine the influece of: (1) rotor and stator radii; (2) stator segment angular width and position with respect to the contact point; and (3) dielectric properties and dimensions (e.g., insulator thickness on rotor) of motor materials. Dynamic modelling is being used in the comparison of predicted and observed motor behavior, and for the study of the effects of stator segment recruitment logic. A number of eccentric-motion micromotors constructed via different fabrication techniques, have been operated. Electro-discharge machining (EDM) is the fabrication method of choice for the prototypes presently used for experimental studies. Typical rotor diameters for the EDM motor are about 500 μm, with lengths of 500 μm. Motor operation has been achieved with commutation rates in excess of 120 000 r.p.m.

CB: A Humanoid Research Platform for Exploring NeuroScience

This paper presents a 50 degrees of freedom humanoid robot, CB -Computational Brain. CB is a humanoid robot created for exploring the underlying processing of the human brain while dealing with the real world. We place our investigations within real world contexts, as humans do. In so doing, we focus on utilising a system that is closer to humans - in sensing, configuration and performance. The real-time network-based control architecture for the control of all 50 degrees of freedom will be presented. The controller provides full position/velocity/force sensing and control at 1 KHz, allowing us the flexibility in deriving various forms of control schemes. Three aspects of the system are highlighted in this paper: 1) physical power for walking; 2) full-body compliant control - physical interactions; 3) perception and control - visual ocular-motor responses

Robotic grasping apparatus

A robotic grasping manipulator includes a support base, a fixed elongate index finger which extends forwardly a certain distance from the base and then curves upwardly to terminate in a tip, and a two-degree of freedom elongate thumb pivotally attached at a proximal end to the base to extend generally forwardly therefrom to terminate in a distal end which may be moved vertically and laterally with respect to the fixed finger to thereby enable holding objects between the finger and thumb. Also included is a moveable elongate finger pivotally attached at a proximal end to the base to extend forwardly a certain distance and then upwardly, generally alongside the index finger, to terminate in a distal end. The distal end may be moved laterally away from and toward the index finger to thereby enable holding objects between the two fingers. With the two-degree of freedom movement of the thumb and the one-degree of freedom movement of the moveable finger, a variety of different shaped objects may be grasped and held between the two fingers and thumb.

Antagonistic control of a tendon driven manipulator

Two antagonistic control algorithms are described. These algorithms are used to control manipulator links which are antagonistically driven by two actuators via tendons. They have been simulated and experimentally shown to produce better active and passive performance for an electric test system than control algorithms developed earlier. The algorithms use both positive and negative (push and pull) commands to be given to the actuators. Previous systems generated only pull commands, ensuring that tendons would not go slack and give rise to backlash and other problems. The proposed controllers allow push commands to the actuators but still do not allow tendons to go slack. Each actuator, in addition to being fed back its respective tendon force, is fed back both positive and negative manipulator joint torques. This feature allows both actuators to simultaneously respond to torque errors.<<ETX>>

The wobble motor: an electrostatic, planetary-armature, microactuator

A variety of micromotor concepts has been evaluated, with the wobble motor (WM) approach being one of those selected for extensive study. Various WM configurations have been analytically evaluated using finite-element methods and closed-form solutions. Important performance characteristics have been estimated such as stall torque and free speed, and alternate strategies for motor control have been examined. Five motor configurations and a variety of silicon-based and non-silicon-based fabrication techniques have been examined in detail. In exploratory exercises, motors have been fabricated using direct mechanical assembly, electro-discharge machining (EDM), cylindrical photolithographic etching, and coextrusion of metal and plastic. The EDM approach was selected as the motor alternative which could function as an experimental testbed. Fifteen EDM WMs have been constructed and utilized for experimental purposes. Experiments aimed at generating simple preliminary data have been conducted, and results compare reasonably to analytical studies.<<ETX>>

A full tactile sensing suite for dextrous robot hands and use in contact force control

A full tactile sensing suite for the finger segments and palm of the Utah/MIT dextrous hand is presented. The rubber-based sensors employ capacitance sensing and floating electrodes in the top layer, and contain local electronics for excitation, filtering, analog-to-digital conversion, and serial communication. Experimental results on static, dynamic, and spatial properties are presented. Use of the tactile sensor in contact force control is demonstrated.

Control strategies for tendon-driven manipulators

Two antagonist control algorithms are presented. These algorithms are used to control manipulator links antagonistically driven by two actuators via tendons. They have been simulated and experimentally shown to produce better active and passive performance for an electric test system than control algorithms developed earlier. There are two fundamental differences between the control algorithms and earlier ones. First, the new algorithms allow both positive and negative (push and pull) commands to be given to the actuators. Previous systems generated only pull commands, ensuring that tendons would not go slack and give rise to backlash and other problems. The new controllers allow push commands to the actuators, but still do not allow tendons to go slack. Second, each actuator, in addition to being fed back its respective tendon force, is fed back both positive nd negative manipulator joint torques. This feature allows both actuators to respond simultaneously to torque errors.<<ETX>>