Inverse optimal control for speed-varying path following of marine vessels with actuator dynamics
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Tracking error
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The UK ATC has developed a novel thermal actuator design as part of an OPTICON project focusing on the development of a Freeform Active Mirror Element (FAME). The actuator uses the well understood concept of thermal expansion to generate the required force and displacement. As heat is applied to the actuator material it expands linearly. A resistance temperature device (RTD) is embedded in the centre of the actuator and is used both as a heater and a sensor. The RTD temperature is controlled electronically by injecting a varying amount of current into the device whilst measuring the voltage across it. Temperature control of the RTD has been achieved to within 0.01°C. A 3D printed version of the actuator is currently being used at the ATC to deform a mirror but it has several advantages that may make it suitable to other applications. The actuator is cheap to produce whilst obtaining a high accuracy and repeatability. The actuator design would be suitable for applications requiring large numbers of actuators with high precision.
Repeatability
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One of the methods to improve the thrust of a drone rotor is to attach an external guide composed of a bottom plate and cylindrical side plates around the outer circumference of the rotor blades. Although its thrust force has been studied in previous research, its efficiency as a thrust system is still unknown. In this study, the efficiency of the thrust system is evaluated from the thrust force and power consumption of the thrust system. Experimental results show that the thrust increases by 15% and the power consumption per rotor power decreases by 7%. The “figure of merit” (FM) also increases by 0.1 with the addition of the external guide.
Drone
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We report on the development of a nano-Newton thrust-stand that can measure up to 100 μN thrust from different types of microthrusters with 10 nN resolution. The compact thrust-stand measures the impingement force of the particles emitted from a microthruster onto a suspended plate of size 45 mm × 45 mm and with a natural frequency over 50 Hz. Using a homodyne (lock-in) readout provides strong immunity to facility vibrations, which historically has been a major challenge for nano-Newton thrust-stands. A cold-gas thruster generating up to 50 μN thrust in air was first used to validate the thrust-stand. Better than 10 nN resolution and a minimum detectable thrust of 10 nN were achieved. Thrust from a miniature electrospray propulsion system generating up to 3 μN of thrust was measured with our thrust-stand in vacuum, and the thrust was compared with that computed from beam diagnostics, obtaining agreement within 50 nN to 150 nN. The 10 nN resolution obtained from this thrust-stand matches that from state-of-the-art nano-Newton thrust-stands, which measure thrust directly from the thruster by mounting it on a moving arm (but whose natural frequency is well below 1 Hz). The thrust-stand is the first of its kind to demonstrate less than 3 μN resolution by measuring the impingement force, making it capable of measuring thrust from different types of microthrusters, with the potential of easy upscaling for thrust measurement at much higher levels, simply by replacing the force sensor with other force sensors.
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Piezoelectric actuators are being used in increasingly complex structures. An actuator that can be removed and used again would be beneficial in testing actuator placement before the permanent actuator would be attached. Furthermore, an actuator that has similar response characteristics to the permanent actuator would be beneficial in estimating the response characteristics of the actuator before it is attached. A concept for such a removable, reusable actuator has been developed, constructed, and used. This paper describes the differences in authority among three removable, reusable actuators as compared to a permanent actuator. The permanent actuator is bonded to the host structure with only strain gauge cement. This paper also quantifies the changes in authority of the three removable, reusable actuators as they are removed several times from the host structure. When comparing removable and permanent actuators, the stiffer bonding technique typically had greater actuation authority. When comparing authority reduction of removable actuators over ten applications of the actuator, greater reduction occurred with actuators that incorporated a stiffener.
Rotary actuator
Strain gauge
Pneumatic actuator
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The measured thrust could be distorted because of the transient response of thrust stand during combustion of rocket motor. As a result of the distorted thrust, it is not easy for us to know the values of thrust peak and thrust duration time. Therefore, it is of great importance to compute the true thrust from the measured thrust. In this study the method to eliminate the transient response from the measured thrust using only the measured thrust was Proposed, and also experimental data were used to approve the proposed method. The result showed that the proposed method would be available to compute the true thrust.
Transient (computer programming)
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This paper demonstrates the effect of dynamic load conditions on the design and performance of actuators. Actuators have both active and passive properties that determine their overall performance. The interaction between the active and passive components of an actuator, and hence the performance, will depend on both the objective (i.e., the actuator used in a control system or as a source) and the dynamics of the structure to which the actuator is attached. It is shown that it is mainly the active properties of an actuator which are affected by the load conditions of the structure. Changes in the active properties due to varying load conditions are demonstrated for various actuator types. By altering the passive properties of an actuator (i.e., mass and stiffness) it is possible to enhance the performance of the actuator used in a particular application. It is shown that the optimal actuator design depends on both the dynamics of the structure to which the actuator is attached and the performance objective. It will be demonstrated that actively changing the passive properties of an actuator allows significant enhancement of performance.
Plant
Plasma actuator
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Constant (computer programming)
Rocket (weapon)
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Existing actuator controls are typically designed based on optimizing performance and robustness to system uncertainties, without considering the operational lifetime of the actuator. It is often desirable, and sometimes necessary, to trade off performance for extended actuator operational lifetime. This paper introduces the concept of incorporating the actuator lifetime as a controlled parameter. We describe preliminary methods for speed/position tracking control of an electromechanical actuator (EMA) while maintaining a desired minimum lifetime of the actuator motor
Robustness
Position tracking
Rotary actuator
Plant
Position (finance)
Pneumatic actuator
Valve actuator
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