Distributed control architecture for real-time telerobotic operation

The emerging field of telerobotics places new demands on control system architecture to allow both autonomous operations and natural human-machine interfacing. The feasibility of multiprocessor systems performing parallel control computations is realizable. A practical distribution of control processors is presented and the issues involved in the realization of this architecture are discussed. A prototype dual axis controller based on the NOVIX computer is described, and results of its implementation are discussed. Application of this type of control system to a replicated, redundant manipulator system is also described

Control and electronic subsystems for the advanced servomanipulator

The advanced servomanipulator (ASM) represents a new generation of electrically driven force-reflecting manipulator systems designed to be remotely maintainable. This ASM is being developed to perform remote maintenance in a nuclear fuel reprocessing plant where human access is not allowed. The primary function of the manipulator control system is to maintain stable, accurate master/slave operation while providing sensitive force reflection to the operator. The control system is based upon tightly coupled distributed digital microprocessing methods. The architectural structure of the control system is outlined and is compared to the previously developed Model M-2 control system, and justification for the advances incorporated into the ASM structure are given. The various modes of operation and diagnostics are described, and throughput requirements associated with joint servo-control and counter-balancing are discussed. The fundamental elements of the control system are reviewed, including the processor selection (Motorola MC68000) and the language (FORTH). The purpose of this document is to review the design decisions and the resulting design selections to serve as a base for future improvements. Four main areas will be covered: (1) system overview, (2) hardware implementation, (3) software partitioning, and (4) remote electronics considerations. Each area will address the specifics of the selected equipment or the functional requirements of the control method. 9 references, 4 figures

Low temperature specific heat of YBa₂Cu₃O_7−δ

For T < 0.4K, the specific heat of YBa2Cu3O7−gd (δ = 0.13 and 0.99) can be decomposed into a nuclear term αT−2 and a linear term γT (γ = 20–30 mJ/KZ mole), which is strongly depressed by increasing the temperature as well as the external magnetic field. We attribute the γT term to a spin-glass type freezing mechanism. The large a-value (54 μJ/K mole) found for δ = 0.13 indicates considerable Zeeman splitting of nuclear spin states in the absence of both long-range magnetic order and an external magnetic field

Observation of a Thermal Expansion Anomaly at 36 K in La₂CuO₄: Evidence for a Structural Phase Transition

We report results for the thermal expansion, α(T), of La2CuO4 and La1.85Sr0.15CuO4. Both compounds exhibit surprisingly similar anomalies in α(T) near 36 K. While for the Sr-doped compound this anomaly is shown to indicate bulk superconductivity, for La2CuO4 it has to be attributed to a structural phase transition. Our results suggest that the onset of superconductivity, both in minor parts of the volume in La2CuO4 and in the bulk of La1.85Sr0.15CuO4, is accompanied and possibly even triggered by this structural transition

Specific heat, resistivity and neutron scattering studies in the Kondo lattice CeNi₂Ge₂

Specific heat, resistivity and inelastic neutron scattering experiments are reported, which demonstrate that CeNi2Ge2 exhibits a heavy-fermion groundstate which is neither magnetic nor superconducting. The specific heat coefficient γ(T) reaches 350 mJ/K2mol and exhibits a peak at 0.4 K showing that coherence effects become important at low temperatures. The magnetic relaxation rates as measured via the line width in inelastic neutron scattering experiments are strongly enhanced and deviate from a Korringa law behaviour. The Kondo temperature TK ≈ 30 K was determined from the magnetic relaxation rates and from the specific heat data

Coexistence of spin-glass freezing and heavy-fermion superconductivity in Ce_1−xGd_xCu_2.2Se₂

In Ce1−xGdxCu2.2Si2 spin-glass ordering coexists superconductivity below the “critical” (Tc → 0) concentration xcr = 5.1 at%. For samples with slightly lower Gd content, a small volume fraction of ⋍ 10% remains superconducting presumably due to demagnetizing effects. Thus, the full Tc(x) dependence is accessible. It closely follows the AG-result and proves the existence of a “paramagnetic” pair-breaking mechanism

Low-Temperature Specific Heat in High Magnetic Field of Bi₂Sr₂CaCu₂O₈

The specific heat C(T) of Bi2Sr2CaCu2O8 was measured at 80 mK ≤ T ≤ 40 K and in magnetic fields up to 8 T. For T ≤ 400 mK, C(T) is well described by C(T) = γ* centerdot T + α/T2. For increasing temperature as well as for increasing magnetic field, the coefficient γ* of the linear term is strongly depressed. This result is interpreted best in terms of spin-glass physics due to a very low (≈ 0.1%) concentration of localized Cu2+ moments, consistent with the absence of any sizeable Curie term in the normal-state magnetic susceptibility