Tech Briefs

This novel algorithm automatically compensates for the errors introduced by physical factors, enabling the control system to adjust the applied force accurately.

Researchers at NASA's Armstrong Flight Research Center have developed a new technology to reduce inaccuracies in force/haptic feedback devices and systems. Used at NASA in aircraft simulations for force feedback pilot controls, these systems involve a servomotor applying precise force to a specific point based on very accurate measurements. However, because the force instrumentation often cannot be placed directly at the point of interest, a mechanical assembly is used, linking the force transducer to the target point. Unfortunately, this mechanical assembly introduces inaccuracies due to its own forces of gravity, friction, and inertia.

NASA Armstrong's innovative algorithm, developed for a subsonic research aircraft simulator, can be applied to other automated mechanical servo systems.

Traditionally, engineers have had to build an inflexible, application-specific system to minimize these inaccuracies. Now they have a new option. Recognizing the advantages of being able to connect a generic servo system to any mechanical assembly, NASA Armstrong researchers have developed a compensation algorithm that uses an automatic calibration method to actively correct for gravity, friction, and inertia forces introduced in the force feedback system.

Requiring little user input, the innovation increases the accuracy of the applied force, and permits the force measurement to reflect the true force at the point of interest. Specifically, the compensation algorithm uses the calibration data to determine the amount of force to add to or subtract from the force transducer reading. The innovation performs the automatic calibration for each axis of motion on an individual basis, and the compensation algorithm treats each axis of motion independently. Two feedback devices — regarding position and force — complete the closed-loop control. The outcome is a more accurate measure of the force at the point of interest, which allows the control algorithm to adjust the magnitude of the command to compensate for the losses or gains caused by the mechanical assembly.

Enabling the control algorithm to actively adjust the applied force effectively reduces errors, which is relevant for any automated mechanical servo system where accurate force is required in a location different from that of the force transducer. Such systems are used in robotics, mobile devices, medical surgeries, video games, virtual reality, and some manufacturing processes.

This work was done by Michael Hill of Armstrong Flight Research Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact NASA Armstrong Technology Transfer Office at 661-276-3368 or by e-mail at This email address is being protected from spambots. You need JavaScript enabled to view it.. DRC-013-041

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