The validation of computational-fluid-dynamics (CFD) software used for the design and analysis of turbomachinery has made it necessary to resolve measurement of the flow field more finely by recording more points per survey. The demand for these measurements has resulted in additional requirements for the actuation systems used to move flow-measuring probes in testing facilities. An electronic computer-based programmable motion system (PMS) has been developed to satisfy these requirements. The system is designed to be user-friendly and versatile, giving the user many features not available in older probe-positioning systems. Although originally developed to control probe actuators, the PMS can also be used to control the actions of movable stator vanes, laser tables, or other devices that accept velocity control signals from -10 to 10 Vdc.

The PMS can be used to control as many as 18 axes of motion. The system (see Figure 1) comprises three main parts: a programmable logic controller (PLC), a human/machine interface (HMI), and a motor-drive subsystem. The PLC is used for main control of the system. The HMI is implemented in software on a personal computer. The motor-drive subsystem includes motor-drive circuits and dc brushless motors.

Figure 1. The Programmable Motion System offers enhanced capabilities for controlling as many as 18 axes of motion. For simplicity, only one actuator is shown here. A dedicated motion-control module, motor drive, and motor are needed for actuation on each axis.

The PLC, HMI, and motor-drive subsystem all operate together to effect control of speeds and positions for the various axes. The position control loop for each axis is implemented in the PLC. The velocity control loop for each axis is implemented in the motor-drive subsystem or in motion modules in the PLC, depending on the application. Commands from the user are sent to the PLC via the HMI program. The interface to the data-acquisition system is implemented in the PLC. The interface to motion profiles specified by the user resides in the HMI program.

The PMS enables its user to control the speed, position, and other parameters of motion for each axis (see Figure 2). The user can also create and edit motion profiles and cause the execution of the motions by use of the Microsoft Excel program. The system can interact with standard data-acquisition systems at Glenn Research Center and with other data and control systems.

Figure 2. The Run Menu is a display, generated by the human/machine interface, through which the user controls motions along or about the various axes. The run menu includes an axis control panel, an access display, and an area for functions defined by the user.

In its initial application, the PMS is used to control three sets of circumferential, radial, and yaw probe actuators in an aeronautical test facility at Glenn Research Center. The standard modes of operation for positioning, characterized in terms of motions, are: move to a specified absolute position, move a specified positive or negative increment from the present position, find the home position, and jog (positive or negative). In addition, a yaw probe can be moved in a nulling mode, in which its position is adjusted in response to the output of a differential-pressure transducer. The versatility of the system makes it suitable for a variety of applications.

The PMS has the following advantageous features:

  • For the researcher, one of the best features of the PMS may be that it functions with minimal (relative to other probe-actuation systems) communication overhead and, as a result, the measurement time is relatively short at 6 seconds per data point.
  • The PMS is electrically clean; that is, its electronic circuitry does not affect such instrumentation as pressure transducers and hot-wire probes.
  • Real-time editing of axis parameters, integrated profile programming, and point-and-click mouse input serve to simplify operation.
  • The system can accommodate auxiliary positioning devices on the driven ends (in contradistinction to the driv-ing ends), and in operation, the system maintains continuous communication with the data-acquisition system used in the initial application. These features are helpful for obtaining accurate and repeatable results.
  • Functions specific to a test can be programmed in the field.
  • The system is independent of specific motor-drive circuits or motors.
  • Troubleshooting is easy.
  • The system can be upgraded or expanded.

The PMS gives the user more flexibility than do older probe-actuation systems. Initial tests have shown that data-taking time is 30 to 40 percent shorter. Copies of the PMS are scheduled to be installed in at least four other aeronautical test facilities at Glenn Research Center.

This work was done by Brent C. Nowlin and L. Danielle Koch of Glenn Research Center. LEW-16690


NASA Tech Briefs Magazine

This article first appeared in the November, 1999 issue of NASA Tech Briefs Magazine.

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