Characterization and control of self-motions in redundant manipulators

The presence of redundant degrees of freedom in a manipulator structure leads to a physical phenomenon known as a self-motion, which is a continuous motion of the manipulator joints that leaves the end-effector motionless. In the first part of the paper, a global manifold mapping reformulation of manipulator kinematics is reviewed, and the inverse kinematic solution for redundant manipulators is developed in terms of self-motion manifolds. Global characterizations of the self-motion manifolds in terms of their number, geometry, homotopy class, and null space are reviewed using examples. Much previous work in redundant manipulator control has been concerned with the redundancy resolution problem, in which methods are developed to determine, or resolve, the motion of the joints in order to achieve end-effector trajectory control while optimizing additional objective functions. Redundancy resolution problems can be equivalently posed as the control of self-motions. Alternatives for redundancy resolution are briefly discussed

A "Sidewinding" Locomotion Gait for Hyper-Redundant Robots

This paper considers the kinematics of a novel form of hyper-redundant mobile robot locomotion which is analogous to the 'sidewinding' locomotion of desert snakes. This form of locomotion can be generated by a repetitive travel wave of mechanism bending. Using a continuous backbone curve model, we develop algorithms which enable travel in a uniform direction as well as changes in direction

t* for S waves with a continental ray path

The purpose of this study was to determine t* for S waves with ray paths under the continental United States. The data set consists of long- and short-period body waves from the Borrego Mountain earthquake as observed in the northeastern U.S. The P wave forms are dominated by the sP phase and the SH wave forms by the sS. It is assumed that there are no losses in pure compression so that the relative attenuation rate of P and S waves is known. The initial source radiation is determined from the sP phase and the value of t_β* from the spectral content of the S wave. The results indicate that t_β* is 5.2 ± 0.7 sec along this ray path. Long- and short-period body waves from some deep South American events are used to test for lateral asymmetry of the Q distribution under the U.S. No lateral amplitude variation exists in this data, but this result is difficult to correlate with many previous results. The t_ β* value for a 600-km deep earthquake appears to be about 3 sec. A comparison of these values with values computed from current models of the Earth's Q distribution indicates that the models are slightly too high in Q overall and that more of the total body-wave attenuation occurs above 600 km than is indicated by the models

Historical Earthquake Sequences

A rudimentary seismic network has existed in the United States since the mid 1920' s. Many important earthquakes in mid-size range (5 < M < 6), have been recorded by the relatively low gain instruments from this network, Galitzin's and Wood-Anderson torsions. Because the networks were so sparse, they have not been effectively used. In this report, we have examined records collected form the 1946 Walker Pass and 1947 Manix events and conducted a pilot study into how these records can be used in conjunction with modern data to understand the characteristics of these historic events. One well-proven method for assessing old events is to compare existing historic recording with observations from modern events (calibration event). The 1962 Walker Pass event (M_L= 4.9) was studied in detail for this purpose and observations at Pasadena (PAS) and Florisent (FLO), Missouri compared with the 1946 mainshock and foreshock (M_L = 5.2). This comparison yields a M_o = 1.2 x 10²⁵ for the main event with the foreshock estimate lower by about a factor of 3 to 5. The mechanisms do not seem to be the same but all three events are relatively deep. A comparison of these events with the Manix event recorded at these two stations as well as at Weston, MA indicate that the Manix event is considerably larger. A detailed modeling effort was conducted on the (PAS) local strong motion recordings of the events separately and in conjunction with the bodywaves recorded at FLO. Considerable effort was devoted to calibrating the upper-mantle model needed in generating the synthetics at FLO. Our best estimate for the Walker Pass mainshock is that it had a strike, dip, and rake of (0°, 40°, 70°) with a moment of 1.5 x 10²⁵ ergs, and occurred at a depth of 20 km. Results for the Manix event proved similar to those reported by Doser (1990); essentially a strike-slip event with (65°, 85°, 8), a moment of 3.5 x 10²⁵ ergs and a depth of 6 km

Electrolysis-based diaphragm actuators

This work presents a new electrolysis-based microelectromechanical systems (MEMS) diaphragm actuator. Electrolysis is a technique for converting electrical energy to pneumatic energy. Theoretically electrolysis can achieve a strain of 136 000% and is capable of generating a pressure above 200 MPa. Electrolysis actuators require modest electrical power and produce minimal heat. Due to the large volume expansion obtained via electrolysis, small actuators can create a large force. Up to 100 µm of movement was achieved by a 3 mm diaphragm. The actuator operates at room temperature and has a latching and reversing capability

Integrated parylene-cabled silicon probes for neural prosthetics

Recent advances in the field of neural prosthetics have demonstrated the thought control of a computer cursor. This capability relies primarily on electrode array surgically implanted into the brain as an acquisition source of neural activity. Various technologies have been developed for signal extraction; however most suffer from either fragile electrode shanks and bulky cables or inefficient use of surgical site areas. Here we present a design and initial testing results from high electrode density, silicon based arrays system with an integrated parylene cable. The greatly reduced flexible rigidity of the parylene cable is believed to relief possible mechanical damages due to relative motion between a brain and its skull

Eccentricity estimator for wide-angle fovea sensor by FMI descriptor approach

This paper proposes a method for estimating eccentricity that corresponds to an incident angle to a fovea sensor. The proposed method applies Fourier-Mellin Invariant descriptor for estimating rotation, scale, and translation, by taking both geometrical distortion and non-uniform resolution of a space-variant image by the fovea sensor into account. The following 2 points are focused in this paper. One is to use multi-resolution images computed by discrete wavelet transform for reducing noise caused by foveation properly. Another is to use a variable window function (although the window function is generally used for reducing DFT leakage caused by both ends of a signal.) for changing an effective field of view (FOV) in order not to sacrifice high accuracy. The simulation compares the root mean square (RMS) of the foveation noise between uniform and non-uniform resolutions, when a resolution level and a FOV level are changed, respectively. Experimental results show that the proposed method is consistent with the wide-angle space-variant image by the fovea sensor, i.e., it does not sacrifice high accuracy in the central FOV