MODAL 50A Exciter with Lateral Excitation Test Stand

Company: MB Dynamics, Inc.
Category: Measurement & Inspection Product of the Year

The 1” pk-pk continuous stroke (optional 30 mm pk-pk) of the MODAL 50A exciter, with 1.1” between stops, offers reliable and sufficient excitation for both flexible structures and low-frequency “suspended shaker” tests. Its lightweight (less than 0.33 lbs.) armature provides a reliable excitation source for the modal testing of small articles with minimized mass loading. A unique armature design allows for important and dramatic reductions in force drop-off at test article resonances. In addition, the MODAL 50A’s broad usable frequency range, from DC to 5000 Hz, allows it to accommodate virtually any modal survey type, including multi-shaker random, single-point random, multi-point sine dwell, and burst random.

The relatively compact (11.5” x 7.5” x 9.25”) and lightweight (55 pounds inclusive of trunnion base) footprint of the MODAL 50A further facilitates its ease of installation within space constrained environments. The exciter, its easy-mount inertial masses, and related accessories may be easily setup and operated by a single person, including in remote locations. The trunnion base of the MODAL 50A incorporates two unique hand-knobs and three screw feet, allowing for exciter adjustments to be performed at virtually any excitation angle. A quick connect/disconnect feature for additional masses is also used to provide large inertial restraint during low-frequency modal testing, while a series of quick disconnect turnbuckles allow for both adjustable suspension and ease of 6DoF positioning. Low armature axial suspension stiffness (<15 lbs./in) further ensures that MODAL 50A exciter dynamics may be decoupled from the test specimen. The exciter can also drive cable lengths ranging from 30 to 100 (optional) feet.

The use of streamlined onboard fixturing simplifies the process of attaching the MODAL 50A to a test structure. The fixturing includes a center bore clearance hole which extends through the armature, housing, trunnion base and inertial masses, allowing for unlimited shaker positioning along the stinger axis. A collet chuck allows for gripping of either a “one size fits all” threadless stinger or a “piano wire” stinger, in sizes from 0.020″ to 0.12″ (0.5 to 3.0 mm). Use of the “piano wire” stinger decouples force inputs in all directions except for that of the driven axis, thereby avoiding cross-axis force measurement errors. An oscillatory force of 50 pounds keeps required preloaded tension to the stinger, thereby eliminating buckling problems, while still delivering exciter peak dynamic force. These and other combined features allow the MODAL 50A exciter to provide superior forcing functions, along with the virtual elimination of common measurement errors associated with bending moments, side loads, and end-user reliance on traditional stinger compression loading functionality.

Recommended optional accessories for the Modal 50A exciter, also available from MB Dynamics, include the MB500VI amplifier; an exciter system accessory kit; and its newly introduced lateral excitation test stand.

Featuring seamless compatibility with both the company’s MODAL 50A and MODAL 110 exciter systems, the new lateral excitation test stand from MB Dynamics provides versatile horizontal or vertical suspension and overall system exciter support during experimental modal surveys, including greater distributed input energy uniformity and improved signal-to-noise ratios.  It does so, by offering versatile exciter suspension and support, as well as by applying force to a test structure in one of two unique ways: either horizontally, into the side of a test structure; or, obliquely, beneath a test structure. The stand further allows exact modal exciter positioning, in either horizontal or vertical direction, while still accommodating a maximum suspended load of up to 60 kg.

The Lateral Excitation Stand may be used in combination with tensioned piano wire or compression stingers to help reduce measurement errors arising from unmeasured transverse forces. This, given that tension-only stingers can be used to apply axial forces without the typical sideloads which can otherwise contaminate measured data. When a piano wire stinger is properly suspended via four supplied turnbuckles, it connects to a test item’s force sensor via the modal exciter’s through-hole and corresponding base, along with required inertial masses. The piano wire stinger then wraps around a pulley. Any required static preload force is applied via a small hand winch, with a series of quarter-turn handles used to secure the lateral arm and pulley. A low gear-ratio hand crank facilitates easy vertical adjustments of the suspended stinger over a range of 305 mm to 1415 mm. Upon application of sufficient static preload forces, as to exceed dynamic force, the piano wire stinger is secured by tightening the Dumore Chuck within the exciter’s moving element.

As the Lateral Excitation Stand allows the modal exciter to be set atop its lateral arm and rotated more precisely about its trunnion base, the stand allows for the MODAL 50A or MODAL 110 to therefore provide excitation at virtually any angle, with up to a 300 mm horizontal adjustment rate, and with exciter motion properly isolated from the test stand.