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An advanced design and implementation of a Control Architecture for Long Range Autonomous Planetary Rovers is presented using a hierarchical top-down task decomposition, and the common structure of each design is presented based on feedback control theory.
A recently developed micro-commanding rotational-position-control system offers advantages of less mechanical complexity, less susceptibility to mechanical resonances, less power demand, less bulk, less weight, and lower cost, relative to prior rotational-position-control systems based on stepping motors and gear drives. This system includes a digital-signal- processor (DSP)-based electronic controller, plus a shaft-angle resolver and a servomotor mounted on the same shaft. Heretofore, micro-stepping has usually been associated with stepping motors, but in this system, the servomotor is micro-commanded in response to rotational-position feedback from the shaft-angle resolver. The shaft-angle resolver is of a four-speed type chosen because it affords four times the resolution of a single-speed resolver. A key innovative aspect of this system is its position-feedback signal- conditioning circuits, which condition the resolver output signal for multiple ranges of rotational speed. In the preferred version of the system, two rotational- speed ranges are included, but any number of ranges could be added to expand the speed range or increase resolution in particular ranges. In the preferred version, the resolver output is conditioned with two resolver-to-digital converters (RDCs). One RDC is used for speeds from 0.00012 to 2.5 rpm; the other RDC is used for speeds of 2.5 to 6,000 rpm. For the lower speed range, the number of discrete steps of RDC output per revolution was set at 262,144 (4 quadrants at 16 bits per quadrant). For the higher speed range, the number of discrete steps per revolution was set at 4,096 (4 quadrants at 10 bits per quadrant).
A motor controller system uses a rotary sensor with a plurality of signal conditioning units, coupled to the rotary sensor. Each of these units, which is associated with a particular range of motor output shaft rotation rates, generate a feedback signal indicative of the position of the motor s output shaft. A controller (i) converts a selected motor output shaft rotation rate to a corresponding incremental amount of rotational movement for a selected fixed time period, (ii) selects, at periodic completions of the selected fixed time period, the feedback signal from one of the signal conditioning units for which the particular range of motor output shaft rotation rates associated therewith encompasses the selected motor output shaft rotation rate, and (iii) generates a motor drive signal based on a difference between the incremental amount of rotational movement and the feedback signal from the selected one of the signal conditioning Units.
Two off-the-shelf instruments combine to control chamber temperature over wide range. Portable controller for environmental test chambers changes temperatures automatically over range of -300 degrees to +400 degrees F (-184 degrees to + 204 degrees C). Unit controls rate of temperature change and time at given temperature. Controller developed to meet NASA Shuttle test requirements.
Time interval measurement and control circuitry for lunar ranging experiment
An analytical investigation has been carried out to determine the responses of a flicker-type roll control incorporated in a missile which traverses a range of Mach number of 6.3 at an altitude of 82,000 feet to 5.26 at an altitude of 282,000 feet. The missile has 80 deg delta wings in a cruciform arrangement with aerodynamic controls attached to the fuselage near the wing trailing edge and indexed 450 to the wings. Most of the investigation was carried out on an analog computer. Results showed that roll stabilization that may be adequate for many cases can be obtained over the altitude range considered, providing that the rate factor can be changed with altitude. The response would be improved if the control deflection were made larger at the higher altitudes. lag times less than 0.04 second improve the response appreciably. Asymmetries that produce steady rolling moments can be very detrimental to the response in some cases. The wing damping made a negligible contribution to the response.
Electronic control systems, data-acquisition instrumentation, and microprocessors require accurate timing signals for proper operation. Traditionally, ceramic resonators and crystal oscillators provided this clock function for the majority of these systems. Over the last few years, MEMS (Micro-Electro-Mechanical Systems) resonator-based oscillators began to surface as commercial-off-the-shelf (COTS) parts by a few companies. These quartz-free, miniature silicon devices could easily replace the traditional crystal oscillators in providing the timing/clock function for many digital and analog circuits. They are reported to provide stable output frequency, offer great tolerance to shock and vibration, and are immune to electro-static discharge [ 1-2]. In addition, they are encapsulated in compact lead-free packages and cover a wide frequency range (1 MHz to 125 MHz). The small size of the MEMS oscillators along with their thermal stability make them ideal candidates for use in space exploration missions. Limited data, however, exist on the performance and reliability of these devices under operation in applications where extreme temperatures or thermal cycling swings, which are typical of space missions, are encountered. This report presents the results of the work obtained on the evaluation of an Ecliptek Corporation MEMS silicon oscillator chip under extreme temperatures.
The recent interest in the use of machine vision for flight vehicle guidance is motivated by the need to automate the nap-of-the-earth flight regime of helicopters. Vision-based stereo ranging problem is cast as an optimal control problem in this paper. A quadratic performance index consisting of the integral of the error between observed image irradiances and those predicted by a Pade approximation of the correspondence hypothesis is then used to define an optimization problem. The necessary conditions for optimality yield a set of linear two-point boundary-value problems. These two-point boundary-value problems are solved in feedback form using a version of the backward sweep method. Application of the ranging algorithm is illustrated using a laboratory image pair.
This paper addresses the problem of the allocation of several flight controls to the generation of specified body-axis moments. The number of controls is greater than the number of moments being controlled, and the ranges of the controls are constrained to certain limits. The controls are assumed to be individually linear in their effect throughout their ranges of motion, and independent of one another in their effects. The geometries of the subset of the constrained controls and of its image in moment space are examined. A direct method of allocating these several controls is presented, that guarantees the maximum possible moment is generated within the constraints of the controls. The results are illustrated by an example problem involving three controls and two moments.
The impact of laminar flow control (LFC) technology on aircraft structural design concepts and systems was discussed and the corresponding benefits were shown in terms of performance and fuel economy. Specific topics discussed include: (1) recent advances in laminar boundary layer development and stability analysis techniques in terms of suction requirements and wing suction surface design; (2) validation of theory and realistic simulation of disturbances and off-design conditions by wind tunnel testing; (3) compatibility of aerodynamic design of airfoils and wings with LFC requirements; (4) structural alternatives involving advanced alloys or composites in combinations made possible by advanced materials processing and manufacturing techniques; (5) addition of suction compressor and drive units and their location on the aircraft; and (6) problems associated with operation of LFC aircraft, including accumulation of insects at low altitudes and environmental considerations.
The sensory subsystem of the JPL robotics project is described. The first sensory instrument is a pair of TV cameras, which provides a stereo view of the area of interest. The second is a laser range finder, which can be aimed in a requested direction and measure distance to a surface point that reflects the beam back. Both instruments are controlled by and are interfaced to computer. The calibration process and basic applications to obtain measurements of the external environment are described.
An investigation at medium to high subsonic speeds has been conducted in the Langley low-turbulence pressure tunnel to determine the static stability and control characteristics and to measure the fin normal forces and moments for a model of a wingless fin-controlled missile. The data were obtained at Reynolds number of 2.1 x 10(6) based on the missile maximum diameter or 17.7 x 10(6) based on missile length; this Reynolds number was found to be large enough to avoid any large scale effects between the test and the expected flight Reynolds number. With the horizontal-fin deflection limited to a maximum of 6 degrees, longitudinally stable and trimmed flight could not be maintained beyond an angle of attack of 17 degrees for a Mach number of 0.88 and beyond 20 degrees for a Mach number of 0.50 for any center-of-gravity location without the use of some auxiliary stability or control device such as jet vanes. Mach number had no appreciable effect on the center-of-pressure positions and only a slight effect on neutral-point position. There was a shift in neutral-point position of about 1 caliber as the angle of attack was varied through the range for which the neutral point could be determined. Yawing the model to angles of sideslip up to 7 degrees had little effect on the longitudinal stability at angles of attack up to 15 degrees; however, above 15 degrees, the effect of sideslip was destabilizing. With the vertical fins at a plus-or-minus 6 degree roll deflection, the rolling moment caused by yawing the model at high angles of attack could be trimmed out up to angles of sideslip of 6.5 degrees and an angle of attack of 26 degrees for a Mach number of 0.50; this range of sideslip angles was reduced to 3 degrees at a Mach number of 0.88. The data indicated that, at lower angles of attack, the trim range extended to higher angles of sideslip. The total normal-force and hinge-moment coefficients for both horizontal fins were slightly nonlinear with both angle-of-attack and fin deflection. The effect of Mach number was to reduce the slopes of the hinge-moment coefficient with angle of attack and deflection angle. In general, the effort of increasing the sideslip angle was to reduce the values of the fin normal-force and hinge-moment coefficients.
Lunar ranging ground station with Varian 620/i control computer
The design of the remote site of a local-remote telerobot control system is described which addresses the constraints of limited computational power available at the remote site control system while providing a large range of control capabilities. The Modular Telerobot Task Execution System (MOTES) provides supervised autonomous control, shared control and teleoperation for a redundant manipulator. The system is capable of nominal task execution as well as monitoring and reflex motion. The MOTES system is minimized while providing a large capability by limiting its functionality to only that which is necessary at the remote site and by utilizing a unified multi-sensor based impedance control scheme. A command interpreter similar to one used on robotic spacecraft is used to interpret commands received from the local site. The system is written in Ada and runs in a VME environment on 68020 processors and initially controls a Robotics Research K1207 7 degree of freedom manipulator.
Motion drive system has been developed for use with interferometers where accurate control of minuscule distance in the 1-micron range is of prime importance. The drive system is applicable to any device that requires extremely accurate positioning control.
The author has identified the following significant results. An operational technique for producing high resolution false color composites of ERTS-1 MSS imagery has been developed. The technique uses standard NASA (NDPF) or EROS black/white data products, and permits a broad range of control on composite color balance and contrast range. The use of an additive color viewer has proven valuable for determining the optimum color balance of composites for effective interpretation. The compositing technique is adaptable for effective interpretation. The technique is adaptable to data from a variety of multispectral imaging systems, including multi-seasonal and multipolarization data. A 50 mile north-trending linear anomaly recognized in ERTS-1 MSS imagery west of Goldfield, Nevada has been confirmed as a steeply west-dipping normal fault, here termed the Paymaster Fault. This structure trends southward from the General Thomas Hills along Paymaster Valley and the east side of Clayton Valley into the Palmetto Mountains. There, it terminates against a less pronounced east-trending transverse anomaly which is also believed to be fault controlled. The Paymaster Fault is the most prominent of several large normal faults which terminate southward against this transverse anomaly.
This work aims at demonstrating the feasibility and impact of Anomalous X-ray Scattering (AXS) in characterizing the multi-range structures of solution-state systems. We will show preliminary investigation of long-range correlations in concentrated aqueous electrolytes with a combination of AXS and molecular dynamics (MD) simulations. We will also start exploring the capability of AXS to capture intra- and inter-molecular structure of dilute molecular systems, and specifically its sensitivity to the chemical environment surrounding active metal sites. We anticipate that the development of this method will help us to understand ion solvation and transport, which affect the performances of, for instance, electrocatalytic cells, as well as to identify/control the intrinsic structural factors that lead to selectivity, efficiency, and stability control during catalysis.
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