Bruno M. Jau

Man-equivalent telepresence through four fingered human-like hand system

The author describes a newly developed mechanical hand system. The robot hand is in human-like configuration with a thumb and three fingers, a palm, a wrist, and the forearm in which the hand and wrist actuators are located. Each finger and the wrist has its own active electromechanical compliance system, allowing the joint drive trains to be stiffened or loosened. This mechanism imitates the human muscle dual function of positioner and stiffness controller. This is essential for soft grappling operations. The hand-wrist assembly has 16 finger joints, three wrist joints, and five compliance mechanisms for a total of 24 degrees of freedom. The strength of the hand is roughly half that of the human hand and its size is comparable to a male hand. The hand is controlled through an exoskeleton glove controller that the operator wears. The glove provides the man-machine interface in telemanipulation control mode: it senses the operators inputs to guide the mechanical hand in hybrid position and force control. The hand system is intended for dexterous manipulations in structured environments. Typical applications will include work in hostile environments such as space operations and nuclear power plants.<<ETX>>

Dexterous telemanipulation with four fingered hand system

The paper briefly describes the semi-anthropomorphic telemanipulation system and discusses the advanced capabilities that were demonstrated in the initial performance evaluation. The systems terminus devices are anthropomorphic: an exoskeleton sixteen degree of freedom (DOF) glove controller that senses human finger forces and backdrives slave motions to every joint of its four instrumented fingers; and a four fingered sixteen DOF anthropomorphic slave hand-wrist-forearm. The master glove is attached to a non-anthropomorphic six DOF universal force-reflecting hand controller (FRHC). The mechanical forearm is mounted to an industrial robot (PUMA 560), replacing its standard forearm. Active electromechanical compliance (AEC) systems for each finger and the wrist provide adjustable compliance, enabling human-like soft grasping. The system is controlled by a high performance distributed control system. Initial performance evaluations focused on tool handling capabilities and astronaut equivalent task executions. Results reveal that the combination of a fingered hand and active compliance enables unprecedented task executions. But it also became evident that complex manipulations require a dual arm robot.

Piezoelectric stack actuator life test

Future NASA interferometer missions require actuators for precision positioning to accuracies of the order of nanometers. For this purpose, commercially available multilayer piezoelectric stack actuators are being considered for driving these precision positioning mechanisms. These mechanisms have potential mission operational requirements that exceed 5 years and the nominal actuator requirements for the most critical actuators on the these missions were estimated from the Modulation Optics Mechanism (MOM) and Pathlength control Optics Mechanism (POM) mechanisms which were developed for the Space Interferometry Mission (SIM). At a nominal drive frequency of two hundred and fifty hertz one mission life is calculated to be 40 Billion cycles. In order to test the feasibility of using these commercial actuators for these applications and to determine the reliability and the redundancy requirements of these actuators a life test study was undertaken. In this study a set of commercial PZT stacks configured in a potential actuator flight configuration (pre-stressed and bonded in flexures) were tested for up to 100 billion cycles. The test flexures allowed for two stacks to be mechanically connected in series. The tests were controlled using an automated Lab-View control and data acquisition system that set up the test parameters and monitored the waveform of the stack electrical current and voltage. The samples were driven between 0 and 20 Volts at 2000Hz to accelerate the life test and mimic the voltage expected to be applied to the stacks during operation. During the life test the primary stack was driven while the redundant stack was open circuited. The stroke determined from a strain gauge and the temperature and humidity in the chamber and the temperature of each individual stack were recorded. In addition other properties of the stacks were measured at specific intervals. These measurements included the displacement from a Capacitance gap sensor and impedance spectra. The degradation in the stroke over the life test was found to be small (&#60;3%) for the primary stacks and estimated to be &#60; 4% for the redundant stacks. It was noted that about half the stroke reduction occurred within the first 10 billion cycles. At the end of the life test it was found that by applying DC voltage levels (100 V) above the life test voltage we could initially recover about half of the lost stroke with again some degradation in the long term. The data up to 100 billion cycles for these tests and the analysis of the experimental results will be presented in this paper. 1,2

Mechanical Description of the Mars Climate Sounder Instrument

This paper introduces the Mars Climate Sounder (MCS) Instrument of the Mars Reconnaissance Orbiter (MRO) spacecraft. The instrument scans the Martian atmosphere almost continuously to systematically acquire weather and climate observations over time. Its primary components are an optical bench that houses dual telescopes with a total of nine channels for visible and infrared sensing, and a two axis gimbal that provides pointing capabilities. Both rotating joints consist of an integrated actuator with a hybrid planetary/harmonic transmission and a twist cap section that enables the electrical wiring to pass through the rotating joint. Micro stepping is used to reduce spacecraft disturbance torques to acceptable levels while driving the stepper motors. To ensure survivability over its four year life span, suitable mechanical components, lubrication, and an active temperature control system were incorporated. Some life test results and lessons learned are provided to serve as design guidelines for actuator parts and flex cables.

Anthropomorphic Four Fingered Robot Hand And Its Glove Controller

The paper describes a new mechanical hand system whose hand looks and functions just like a human hand, except it has no little finger. The hands actuators are located in the forearm, extending the hand structure to the elbow and including the wrist. The hand is controlled through an exoskeleton glove controller that the operator wears. The glove provides the man-machine interface in teleoperational control mode: it senses the operators inputs to guide the mechanical hand in hybrid position and force control. The glove receives positional feedback. A new state of the art control and electronics design was developed for this hand system. Application possibilities are discussed.

Hand trigger system for bi-lateral gripping control in teleoperation

A new device for human operator control of a robotic gripper has been developed and preliminary evaluation has been performed. The JPL Force Reflecting Hand Trigger system features: an instrumented index finger trigger with load cell detection of finger force. A servo controlled, lead screw driven backdrive capability by which the triggers position can be made to follow that of the remotely controlled gripper. And a novel feedback mechanism by which clamping force or some other signal can be fed back via a swiveling motion, also servo controlled, of the trigger surface (force reflection). This system has undergone preliminary testing in which the amount of force reflection is varied and dynamic force tracking response is observed.

Enabling Technologies For High-accuracy Multiangle Spectropolarimetric Imaging From Space

Satellite remote sensing plays a major role in measuring the optical and radiative properties, environmental impact, and spatial and temporal distribution of tropospheric aerosols. In this paper, we envision a new generation of spaceborne imager that integrates the unique strengths of multispectral, multiangle, and polarimetric approaches, thereby achieving better accuracies in aerosol optical depth and particle properties than can be achieved using any one method by itself. Design goals include spectral coverage from the near-UV to the shortwave infrared; global coverage within a few days; intensity and polarimetric imaging simultaneously at multiple view angles; kilometer to sub-kilometer spatial resolution; and measurement of the degree of linear polarization for a subset of the spectral complement with an uncertainty of 0.5% or less. The latter requirement is technically the most challenging. In particular, an approach for dealing with inter-detector gain variations is essential to avoid false polarization signals. We propose using rapid modulation of the input polarization state to overcome this problem, using a high-speed variable retarder in the camera design. Technologies for rapid retardance modulation include mechanically rotating retarders, liquid crystals, and photoelastic modulators (PEMs). We conclude that the latter are the most suitable. Two approaches for using a PEM to achieve high polarimetric accuracy are presented. In the first approach, amplitude modulation , the device is used intermittently to modify the incoming polarization state so that different detectors--those with polarizing filters in different orientations--can be accurately cross-calibrated. In the other approach, synchronous demodulation, signals accumulated during sub-cycles of the modulation are sorted and stored using a high-speed electronic charge-caching circuit built into the detector array.

Alignment mirror mechanisms for space use

The paper describes an optical Alignment Mirror Mechanism (AMM), and discusses its control scheme. The mirrors angular positioning accuracy requirement is ± 0.2 arc-sec. This requires the mirrors linear positioning actuators to have a positioning accuracy of ± 109 nm to enable the mirror to meet the angular tip/tilt accuracy requirement. Demonstrated capabilities are ± 35 nm linear positioning capability at the actuator, which translates into ± 0.07 arc-sec angular mirror positioning accuracy.

The diviner lunar radiometer a mechanical description

The Diviner instrument is a radiometer that is mounted on a two axis gimbal. It observes the lunar surface from aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft. Diviners primary objectives are to map surface temperatures of the entire surface of the Moon at different day and night times. The paper briefly describes the instrument. It focuses on the mechanical implementation, highlighting many of the technical challenges that occurred during its construction. Lessons learned, and design experiences gained, provide future space engineers with guidelines and advice for developing space mechanisms. 1 2

The space interferometer siderostats

The paper describes the Siderostats (SID) of the Space Interferometry Mission (SIM) that is being developed at JPL. The description focuses on the generic design for the SIDs, having a 336 mm diameter mirror with a double corner cube at the mirrors vertex. Mirror positioning is controlled by single stage linear actuators (no fine stage). The mirrors 8° dual axis tip/tilt rotation is enabled through sets of hexfoil flexures. The entire SID configuration is described, key requirements listed, and results from preliminary analyses mentioned. Design details, positioning and sensing capabilities, as well as results from an actuator life test, are presented.