Motion Control

Selecting the Proper Motor for Linear Motion Applications

Linear motion systems are found inside countless machines including precision laser cutting systems, laboratory automation equipment, semiconductor fabrication machines, CNC machines, factory automation, and many others too numerous to list. They range from the relatively simple such as an inexpensive seat actuator in a passenger vehicle, to a complex, multi-axis coordinate system complete with control and drive electronics for closed-loop positioning. No matter how simple or complex the linear motion system, at the most basic level, they all have one thing in common: moving a load through a linear distance in a specific amount of time.

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Design Considerations for Gearmotors in Long-Life Applications

At first glance, the photo at the top is not appealing to any market — a pallet full of old gearmotors is not something one wants to think about after purchasing the necessary gearmotor/motor for their application. But think of it this way instead: these gearmotors were removed from their installation for a refurbishment project after being in service for 30 years. Sandia National Laboratories placed these gearmotors into service in their Heliostat Field in New Mexico in the 1970s. The gearmotors were used to position solar reflectors to concentrate light from all of the individual panels towards one point at the top of a tower. After 30 years, Sandia decided to upgrade the field with a new control system, and they decided to replace the still-operating gearmotors at the same time.

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Redundant Sensors Improve Precision and Reliability

Some machine processes, such as presses, can require extreme accuracy in applying and holding force on an object. A popular way to measure force is via load cells. But what do you do when the accuracy required by a particular application is higher than that guaranteed by the load cell manufacturer?

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Compact Active Vibration Control System

A highly directional actuator can be shaped so that it couples to the response of a flexible structure in the same manner as point sensors. Langley Research Center, Hampton, Virginia This innovation consists of an analog controller, diamond-shaped patch actuator, and point sensors (such as accelerometers). The actuator is designed to couple to the flexural response of the structure in the same manner as a group of point sensors. This results in a co-located transducer pair. The signals from all sensors are combined, filtered, and amplified within the analog controller. The resulting signal is then applied to the actuator, which generates a control force out-of-phase with the measured response. Because the transducers are co-located, the vibration control system is inherently robust to variations in properties of the underlying structure that is being controlled. This type of control system actively suppresses the vibration of a flexible structure using surface-mounted transducers without any external mechanical connections.

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Deep Throttling Turbopump

Marshall Space Flight Center, Alabama Advancement in space exploration necessitates deep throttling of liquid cryogenic rocket engines. Both lunar and Martian robotic and human exploration require engines that can be deep throttled,can start and restart, have a long life, and require minimal maintenance. An engine that is capable of deep throttling at low thrust levels and is versatile enough to accommodate multiple applications would advance the state of the art and enable NASA to meet space exploration objectives. An advanced partial emission turbo pump design is an enabling technology for developing such low thrust level engines. This will complement the current state-of-the-art full emission pump technology.

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Analyzing Rollover Stability of Capsules With Airbags Using LS-Dyna

This method interpolates data to predict the stability boundaries for a capsule on airbags. Langley Research Center, Hampton, Virginia As NASA moves towards developing technologies needed to implement its new Exploration program, studies conducted for Apollo in the 1960s to understand the rollover stability of capsules landing are being revisited. Although rigid body kinematics analyses of the rollover behavior of capsules on impact provided critical insight to the Apollo problem, extensive ground test programs were also used. For the new Orion spacecraft, airbag designs have improved sufficiently for NASA to consider their use to mitigate landing loads to ensure crew safety and to enable reusability of the capsule.

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Test Fixture for Isolation of Vibration Shaker from G-Loading

Combined testing is possible in a controlled, calibrated, and repetitive manner. John F. Kennedy Space Center, Florida The first step in implementing the capability to test sensitive launch vehicle instruments in a combined environment has been completed. The test environment consists of specific vibration spectra induced under sustained Gs, using NASTAR’s ATFS-400 centrifuge. Fixtures allow mounting of the device under test (DUT) to a vibrational shaker in a centrifuge for generating moderate G-loading (1.4 to 9G) such that the vibrational shaker’s capabilities are only slightly affected by the G-loads applied during testing. Two configurations were designed, with the vibrational load parallel to the G-loads, and with the vibration loads transverse (at right angles) to the G-loads. The results are extremely encouraging, and demonstrate the potential of the NASTAR centrifuge to perform this kind of combined testing in a controlled, calibrated, and repetitive manner.

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