November 2003

Penny + Giles has chosen motion control specialist Quin Systems to apply a four-axis linear motor system for simulating and testing feedback sensors used in aircraft control systems.

The LinMot linear controllers are able to simulate a wide range of motion profiles used in advanced airborne platforms such as the AH-64 Apache Longbow Helicopter and RJ45 regional jet. These varying motions are used to test Penny + Giles sensors in demanding aerospace environments, with their associated extremes of temperature, pressure and vibration. For example, they can superimpose a 10Hz 'dither' over a smooth sinusoidal motion, with the ability to alter both the frequency and amplitude of the motion and vibration quickly and easily under software control.

According to Terry Pontin of Penny + Giles, such tests would have been extremely difficult to implement using mechanical linkages such as rotary cams; and orders of magnitude slower to switch between different test parameters. Moreover, pneumatics cannot operate at these frequencies, provide sinusoidal motion, or offer this repeatability.

Said Pontin: "Using the Quin-developed integrated system based on the Linmot controller, we can provide stored motions as needed, then use a serial protocol to select and swap between these motions as required. We use industry-standard Labview software to set up test profiles, which are then downloaded to the LinMot controller to tell it which motion to run."

A total of four axes was needed with two small and two large motors to provide the force needed - small motors moved one potentiometer, whilst the larger ones moved up to four of the transducers, depending upon the frictional forces involved. Motors are mounted outside the environmental test chamber, where temperatures can reach 110°C, and isolated from the heat via nylon couplings and mounting blocks.

LinMot's E400four-axis controller operates from a 240V AC feed, via a 48V power supply. Costs could be kept low, because there is no necessity for costly and complicated three-phase supply; and no requirement for multiple contactors or relays which add further expense.

The servo controllers include a complete digital position-control system, completely eliminating the drift and offset problems encountered with analogue controllers. Further, it is possible to define motion profiles and thus follow adapted motion profiles.

Through the LabView software, Penny + Giles could construct motions within Microsoft Excel, with formulae for the both the 'base motion' and the vibration amplitude and frequency. These were then imported into the LinMot controller and saved.

Linmot proved ideal for the task because motions could be constructed with vibration as needed, then stored and run as required. The test rig made it easy to swap between motions as time intervals specified for each motion. The system was readily interfaced with Penny + Giles transducers, which are direct-acting types, offering zero wear and simple mounting.