This paper presents the application of Inverse Simulation to the control of a mobile robot. The implementation of this technique for motion control has been found to provide highly accurate trajectory tracking. Since the input to the Inverse Simulation is a time history of the desired response, then greater control over the position and orientation of the mobile robot can be achieved. There are many situations where the desired path of a mobile robot is known e.g. planetary rover navigation, factory or warehouse floor, bomb disposal. Typically the robot is either controlled remotely or runs an online controller to navigate the desired path. For a given path, a navigation system generates the desired drive parameters (i.e. heading and velocity) and the associated controllers drive the corresponding actuators. Traditionally the controllers are required to be tuned using knowledge of the limitations of the mobile robot. Inverse Simulation provides a means of generating the required control signals with no need for controller tuning. The use of Inverse Simulation is suitable in cases where the cost of the mobile robot or actuators is high, desired drive requirements need to be met or for situations where tight tolerances on the trajectory are to be achieved. In this paper the benefits of applying Inverse Simulation to the control of a mobile robot are discussed and appropriate results presented.
This work investigates the potential use of direct ultrasonic vibration as an aid to penetration of granular material. Compared with non-ultrasonic penetration, required forces have been observed to reduce by an order of magnitude. Similarly, total consumed power can be reduced by up to 27%, depending on the substrate and ultrasonic amplitude used. Tests were also carried out in high-gravity conditions, displaying a trend that suggests these benefits could be leveraged in lower gravity regimes.
This paper describes the instrumented test-firing of a rocket which seeks to combine the throttleability of a liquid-fueled engine with the simplicity of a solid motor. The concept is that a differentiated fuel and oxidizer rod is forced into a vaporization unit where its constituents transition into separate propellant gases, which are then mixed in a combustion chamber. The vaporization unit is heated by the combustion and the throttle setting is adjusted by changing the force used to drive the solid propellant rod into the vaporizer, which naturally influences the propellant feed rate. In experiments using a solid propellant rod consisting of polypropylene fuel and a 1:1.5 mixture of NH4ClO4 and NH4NO3 oxidizer, we have sustained operations for around sixty seconds. During testing, using propellant feed forces of between 250 N and 900 N, we have achieved propellant feed rates of between 100 mm/min and 300 mm/min, which are in turn correlated to chamber pressures of between approximately 300 kPa and 700 kPa. These correlated cycles of control input (the feed force), throttle response (the propellant feed rate) and implied thrust (the chamber pressure) demonstrate, for the first time, a simple solid rocket that can be throttled in real time.
Future exploration missions to rocky bodies within the Solar System may wish to utilize drill systems on landed vehicles which simply cannot deliver the weight on bit, or accommodate the mass and volume levels which are required for the use of existing drill technology. This issue is being tackled by the development of the Ultrasonic Planetary Core Drill (UPCD) project. This paper shall detail the development effort of this drill to date, describing how lessons learned from early technology have informed the current design. Details of the Concept of Operations, the routine by which the drill samples and caches rocks for later analysis will also be presented, with an emphasis on the effect that the refinement of this process has had on the overall design.
Abstract-Traditional rotary drilling for planetary rock sampling, in-situ analysis and sample return, is challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This article seeks to optimize an ultrasonic-percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view towards building an Ultrasonic Planetary Core Drill (UPCD) device. The UPCD is a descendant of the Ultrasonic/Sonic Driller/Corer (USDC) technique. In these concepts, a transducer and horn (typically resonant at around 20kHz) is used to excite a toroidal free-mass which oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10Hz to 1kHz). This creates a series of stress pulses which are transferred through the drill-bit to the rock surface and, while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, cause fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time-integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free-mass, drill-bit and transducer have been varied and compared in both computer simulation and in practical experiment. The most interesting findings, and those of particular relevance to deep drilling, indicate that increasing the mass of the drill-bit has a limited (or even positive) influence on the rate of effective impulse delivered.
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