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Forming Processes: Monitoring and Control
Published in Osita D. I. Nwokah, Yildirim Hurmuzlu, The Mechanical Systems Design Handbook, 2017
The motor-driven leadscrews have the advantage of being mechanically simple, quieter, and often less expensive than hydraulics. In addition, the leadscrew, if the pitch is high enough, can isolate the actuator from the forming load in such a way as to nearly decouple the actuator dynamics from that of the load. However, leadscrew systems are typically limited to lower loads, owing to limits of the screw threads and nuts, and to lower velocities owing to the high pitches and wear on heavily loaded screw surfaces. Therefore, the vast majority of modern forming machines are hydraulically actuated and use either proportional servo-control of the actuators or a simple form of on-off control.
Digital Transducers
Published in Clarence W. de Silva, Sensor Systems, 2016
In summary, the displacement resolution of an incremental encoder depends on the following factors: Number of windows on the code track (or disk diameter)Gear ratioWord size of the measurement registerExample 11.3A positioning table uses a backlash-free high-precision lead screw of lead 2 cm/rev, which is driven by a servo motor with a built-in optical encoder for feedback control. If the required positioning accuracy is ±10 μm, determine the number of windows required in the encoder track. In addition, what is the minimum bit size required for the digital data register/buffer of the encoder count?SolutionThe required accuracy is ±10 μm. To achieve this accuracy, the required resolution for a linear displacement sensor is ±5 μm. The lead of the lead screw is 2 cm/rev. To achieve the required resolution, the number of pulses per encoder revolution is 2×10−2m5×10−6m=4000pulses/revAssuming that quadrature signals are available (with a resolution improvement of 4), the required number of windows in the encoder track is 1000. The percentage value of physical resolution = (1/4000) × 100% = 0.025%. Consider a buffer size of r bits, including a sign bit. Then, we need 2r−1 = 4000 or r = 13 bits.
Current State of the Design Engineering of the Versatile Test Reactor Plant
Published in Nuclear Science and Engineering, 2022
Steven Unikewicz, Eric Loewen, George Malone
The control rod drive design for the primary control rods and safety rods is derived from the FFTF control rod drive design. The control rod drive mechanism (CRDM) is an electro-mechanical roller nut actuating device used to control the position of neutron absorbers to control core power. When directed to do so by the reactor protection system or loss of system power, the CRDM magnetic field collapses, putting the absorber rod into the core. Each CRDM consists of a lower CRDM assembly, rotor assembly, and stator assembly, which are separately installed in the penetration on the RP. The lower CRDM assembly connects to the control rod driveline. The CRDM drive system energizes and deenergizes the six stators in sequence to cause rotation of the electric field in the stator that causes rotation of the roller nuts which engage a threaded portion of the leadscrew on the lower CRDM assembly. Rotational motion raises or lowers the leadscrew. A bellows seal isolates the roller nut mechanism from exposure to the cover gas and sodium vapor above the sodium-free surface. Deenergizing the stator causes the roller nuts to disengage the leadscrew such that the leadscrew and control rod are released. The downward control rod motion under gravity is enhanced by a spring, force from the bellows, and argon gas pressure inside of the bellows. The CRDM during power operation is always energized to maintain the magnetic field and requires nitrogen cooling flow. The UIS above the core supports control rod driveline guide tubes as well as the IVTM.
Remote-controlled internal lengthening plate for distraction osteogenesis in pediatric patients
Published in Expert Review of Medical Devices, 2019
Jérémie Gaudreau, Mina Mekhail, Reggie Hamdy, Isabelle Villemure
Furthermore, the device’s lengthening position was shown to have a negligible impact on the speed and did not appreciably slow down as the lengthening approached the end of the 50 mm distraction. However, a decrease in lengthening speed was noted with increasing weight on the platform, which is ascribed to the increase in the load on the controller’s motor. However, typical signs of ‘skipping’ or disconnection were not observed in the magnetic drive between the controller and the device. In other words, the relationship between the controller’s rotation and the rotation of the device’s leadscrew remained unaffected, even at slower rate. Consequently, the next iteration of the controller’s design should prescribe the daily increment as a specific number of rotations, instead of a given time interval.
Ruling engines and diffraction gratings before Rowland: the work of Lewis Rutherfurd and William Rogers
Published in Annals of Science, 2018
A little more information did eventually emerge about the second ruling engine in the paper Rogers published in 1884, which was about the problems of producing a ‘perfect’ screw.94 The causes of irregularities were again outlined and the requirements for cutting a screw successfully were stated. A high precision four-inch long screw had soon been made but it did not produce improved gratings.95 This could not have been the original screw in his second ruling engine, because a four-inch screw was not long enough to rule a four-inch grating, but Rogers did not give such details. He cited a speculum metal plate ruled using this short screw with 5000 lines in half an inch (nearly 200 per millimetre) which to the naked eye appeared little different from the gratings of Rutherfurd and Rowland (the latter became available from about 1882), but which was much inferior when tested optically with the spectroscope. Direct attempts to cut a screw half a metre long failed to achieve the accuracy needed but after two years of trials Mr. Van Woerd decided to make a long screw in sections, as a number of ferrules each 1¾ inches (45 mm) long and cut using the same part of the leadscrew of the cutting lathe, which were then placed on a cylindrical shaft and adjusted so that the threads matched. The method was not new, it had been tried and abandoned by Joseph Whitworth. Nominally the screw had eight threads per centimetre, a pitch of 1.25 mm, but comparison with a standard half metre and a standard half yard showed that the pitch was about one part in a thousand less than this. Rogers made a detailed examination of the Van Woerd screw and decided it was ‘pretty certain’ it was the best of its class ever made, but qualified this by saying that if it was found that errors of considerable magnitude remained they should be charged to the method itself. This suggests that the screw had not yet been been tested comprehensively in actual use. There is no indication that other screws were made by this method.