A variety of Industrial applications exist where power ultrasonic elements such as the ultrasonic horn are used. These included the Automotive, Instruments, Foods, Medical, Textiles and Material Joining and Fabrication Industries. In many of these devices the ultrasonic horn is the key component. The standard transducer used in these devices consists of three main parts, the backing, the piezoelectric elements and the horn. Standard horn designs have changed very little since their inception. There are four common types of standard horns. They are; constant, linear, exponential and stepped, which refer to the degree to which the area changes from the base to the tip. A magnification in the strain occurs in the horn that in general is a function of the ratio of diameters. In addition the device is generally driven at resonance to further amplify the strain. The resonance amplification is in general determined by the mechanical Q (attenuation) of the horn material and radiation damping. The horn length primarily determines the resonance frequency. For a 22 kHz resonance frequency a stepped horn of titanium has a length of approximately 8 cm. Although these standard horns are found in many current industrial designs they suffer from some key limitations. In many applications it would be useful to reduce the resonance frequency however this would require device lengths of the order of fractions of meters which may be impractical. In addition, manufacturing a horn requires the turning down of the stock material (eg. Titanium) from the larger outer diameter to the horn tip diameter, which is both time consuming and wasteful. In this paper we will present a variety of novel horn designs, which overcome some of the limitations discussed above. One particular design that has been found to overcome these limitations is the folded horn. In this design the horn elements are folded which reduce the overall length of the resonator (physical length) but maintain or increase the acoustic length. In addition initial experiments indicate that the tip displacement can be further adjusted by phasing the bending displacements and the extensional displacements. The experimental results for a variety of these and other novel horn designs will be presented and compared to the results predicted by theory.
An ultrasonic/sonic driller/corer (USDC) was developed to address the challenges to the NASA objective of planetary in-situ rock sampling and analysis. The USDC uses a novel drive mechanism, transferring ultrasonic vibration into impacts on a drill stem at sonic frequency using a free- flying mass block (free-mass). The main parts of the device and the interactions between them were analyzed and numerically modeled to understand the drive mechanism and allow design of effective drilling mechanism. A computer program was developed to simulate the operation of the USDC and successfully predicted the characteristic behavior of the new device. This paper covers the theory, the analytical models and the algorithms that were developed and the predicted results.
In-situ sampling and analysis is one of the major tasks in future NASA exploration missions. It is essential that the samples acquired on other planets including Mars are free of contaminations from the Earth. Recently, a novel drilling technology that is actuated by a piezoelectric drive mechanism was developed and it is called Ultrasonic/Sonic Driller/Corer (USDC). This drill has an inherent capability to extract the formed drilling powder and thus addresses the critical issue of contamination. A modification of this USDC in the form of an Ultrasonic Rock Abrasion Tool (URAT) allows for the formation of pristine rock surface for analysis. An algorithm is being proposed for the reduction of the contamination that may be generated during the acquisition of the samples. The algorithm could be used to control the flow of particles using programmed vibration characteristics and thus allows for smart flow of particles. The hypothesis is that the probability of a contamination left on the ground surface is exponentially inverse- proportional to the volume of the core ground into dusts. To support this hypothesis, we need to understand the flow pattern of the particles. A model proposed by Savage is used to develop a computer program using finite difference method. Some preliminary results have been derived.
Future NASA exploration missions are increasingly seeking to conduct sampling, in-situ analysis and possibly return samples to Earth for further tests. Missions to Mars are the more near term projects that are seeking such capabilities. One of the major limitations of sampling on Mars and other low gravity environments is the need for high axial force when using conventional drilling. To address this limitation an ultrasonic/sonic drilling/coring (USDC) mechanism has been developed that employs an ultrasonic horn driven by a piezoelectric stack. The horn drives a free mass that resonates between the horn and drill stem. Tests have shown that the USDC addresses some of the key challenges to the NASA sampling objectives. The USDC is lightweight (450 g), requires low preload (< 5N) and can be driven at lower power (5W). The device has been shown to drill rocks with various levels of hardness including granite, diorite, basalt and limestone. The hammering action involved with the coring process can produce cores of various shapes, which need not necessarily be round. Because it is driven by piezoelectric ceramics, the USDC is highly tolerant to changes in its operating environment. These actuation materials can be designed to operate at a wide range of temperatures including those expected on Mars and Venus. Although the drill is driven electrically at 20 kHz, a substantial sub-harmonic acoustic component is found that is crucial to drilling performance. An analytical model has been developed to explain this low frequency coupling in the horn, free mass, drill stem and rock.
Paint stripping from large steel ships and other metallic surfaces is a major environmental safety, cost, and operational challenge in effectively and efficiently maintaining and refurbishing large structures. Environmental concerns are greatly limiting the possible options. As a result, a hybrid system composed of a waterjet with water recycling and robotic mobile manipulators with scanning bridges has become the leading form of paint stripping and was constructed by various manufacturers to address this need. The application of such scanning bridges is slow and their access is constrained by the complex shape of the ship hull and various features on the surface. To overcome these limitations, a robotic system that is called UltraStrip (UltraStrip Systems, Inc., Stuart, FL) is developed. This system uses magnetic wheels to attach the stripper to the structure and travel on it while performing paint stripping. To assure efficient paint stripping feedback data is required to control the travel speed by monitoring the paint thickness before and during the stripping process. Efforts at JPL are currently underway to develop the required feedback capability to assure effective paint stripping. Various possible sensors were considered and issues that can affect the sensitivity, reliability and applicability of the sensors are being investigated with emphasis on measuring the initial conditions of the paint. Issues that affect the sensory data in dynamic conditions are addressed while providing real-time real feedback for the control of the paint stripper speed of travel.
There is increasing realization that some tasks can be performed significantly better by humans than robots but, due to associated hazards, distance, etc., only a robot can be employed. Telemedicine is one area where remotely controlled robots can have a major impact by providing urgent care at remote sites. In recent years, remotely controlled robotics has been greatly advanced and the NASA Johnson Space Center's robotic astronaut, Robonaut, is one such example. Unfortunately, due to the unavailability of force and tactile feedback the operator must determine the required action by visually examining the remote site and therefore limiting the tasks that Robonaut can perform. There is a great need for dexterous, fast, accurate teleoperated robots with the operator's ability to feel the environment at the robot's field. The authors conceived a haptic mechanism called MEMICA (remote MEchanical MIrroring using Controlled stiffness and Actuators) that can enable the design of high dexterity, rapid response, and large workspace haptic system. The development of a novel MEMICA gloves and virtual reality models are being explored to allow simulation of telesurgery and other applications. The MEMICA gloves are being designed to provide intuitive mirroring of the conditions at a virtual site where a robot simulates the presence of a human operator. The key components of MEMICA are miniature electrically controlled stiffness (ECS) elements and Electrically Controlled Force and Stiffness (ECFS) actuators that are based on the use of Electro-Rheological Fluids (ERF). In this paper the design of the MEMICA system and initial experimental results are presented.
A novel ultrasonic drilling and coring device (USDC) was demonstrated to drill a wide variety of rocks: form ice and chalk to granite and basalt. The USDC addresses the key shortcomings of the conventional drills. The device requires low preload and power. The drill bits are not sharpened and, therefore there is no concern to loss of performance due to warring out. The device is not subject to drill walk during core initiation, and does not apply larger lateral forces on its platform. The USDC has produced round and square cores and 14-cm deep holes and has opened new possibilities to the designers of future NASA planetary exploration missions. USDC can be mounted on a Sojourner class rover, a robotic arm or an Aerobot.
Force feedback from remote or virtual operations is needed for numerous technologies including robotics, teleoperated surgery, games and others. To address this need, the authors are investigating the use of electrorheological fluids (ERF) for their property to change the viscosity under electrical stimulation. This property offers the capability to produce feedback haptic devices that can be controlled in response to remote or virtual stiffness conditions. Forces applied at a robot end-effector due to a compliant environment can be reflected to the user using such an ERF device where a change in the system viscosity in proportion to the force to be transmitted. This paper describes the analytical modeling and experiments that are currently underway to develop an ERF based force feedback element.
Future NASA missions in astrophysics, Earth observation, and solar system exploration that require optical communication, optical and infrared imaging, or high precision astrometric measurements impose very stringent demands for the dimensional stability of precision structures and science instrument components. The objective of this paper is to identify the major mechanisms that influence the dimensional behavior of common optomechanical materials, to identify the mechanisms that are important for the proposed missions with critical dimensional stability requirements, and to compare the mission requirements with state-of-the- art material and measurement technologies. This paper discusses the tradeoffs of passive vs. active means of achieving the dimensional stability requirements. The reduction of power consumption and mass, the reliability improvements as a function of the dimensional stability of the structural materials for a typical interferometer are calculated.
Calculations are presented of the coefficient of thermal expansion (CTE) of the radius of curvature of the reflector face sheets made of a quasi-isotropic composite. It is shown that, upon cooling, the change of the CTE of the focal distance of the mirror is equal to that of the radius of the curvature of the reflector face sheet. The CTE of the radius of the curvature of a quasi-isotropic composite face sheet depends on both the in-plane and the out-of-plane CTEs. The zero in-plane CTE of a face sheet does not guarantee mirrors with no focal length changes.
Future NASA missions such as the Great Observatories of the 21st Century require structures which can be maintained with micron to nanometer accuracy. This dimensional stability (OS) must be maintained over the 5 to 10 years of mission lifetime. A high DS, which in this case means the system's ability to retain geometrical properties related to the system's performance, will most likely be achieved by a combination of dimensionally stable materials and active controls. Actively controlled structures can achieve a very high degree of DS. However, the inherent instability of the building blocks limits the ultimate DS which can be realized. This article discusses basic limitations on the DS which can be achieved by an actively controlled system which uses passive materials with limited stability. Thermodynamics limits the ultimately attainable DS. For example, the amplitude of the longitudinal vibration in a space truss structure is related to the temperature of the structure. The amplitude of this axial vibration grows with increasing temperature. Another instability mechanism is the temperature gradients through so called "zero coefficient of thermal expansion (CTE)" materials. "Zero CTE" materials will, under some conditions, show no change in at least one dimension when the material is heated. We will show, that in non-equilibrium conditions "zero CTE" materials can behave as if they had a CTE nearly equal to double the CTE of their stiffest phase. These and other mechanisms influence the space system's performance below 0.1 part per million dimensional stability.