Shaker Configurations and Considerations

Designing an effective electrodynamic shaker system involves more than selecting the right sized shaker; it requires a comprehensive understanding of various configurations and accessories to ensure optimal performance and reliability.

In this article, we’ll explore critical aspects such as trunnion mounting, seismic isolation, and mobility options – highlight solutions like Lin-E-Air pneumatic isolation for enhanced vibration control and discusses the benefits of opto-pneumatic load centering systems that maintain armature alignment during shock testing. Mobility features include rail-guided systems and caster-mounted setups, to facilitate integration with environmental chambers.

After fully understanding your expectations, Jianqiao will work with you to specify the best shaker system and accessories, you’ll need for your specific testing scenarios.The following descriptions apply to most of the shaker systems offered by Jianqiao

Isolation

Pneumatic isolation is not included with the standard shaker or Monobase systems. It is optional and there are several types of isolation:

Neoprene Rubber Pad Isolation: This option is the most basic type of isolation and can isolate as low as 20 Hz. These pads are provided as the standard method of isolation with Monobase systems.

Pneumatic Isolation Mounts: Pneumatic isolation mounts are mounted under the shaker, trunnion, or monobase and are effective to 5 Hz. Jianqiao uses isolation mounts that have steel reinforced side walls for reduced lateral movement.

Lin-E-Air Trunnion Isolation: Lin-E-Air isolation is an extremely effective method to isolate the shaker down to approximately 2 Hz. The isolation uses double pneumatic air bags built into the trunnion. Lin-E-Air is also very effective for horizontal isolation. All monobases for shakers 8,000 lbf (35 kN) and larger include Lin-E-Air isolation mounting.

Seismic Isolation: For very large test articles, seismic isolation may be required to have a proper reaction mass. In this instance, the shaker needs to be directly coupled to the seismic mass through a solid trunnion and the seismic mass must be isolated from the ground. A shaker mounted solidly to a seismic mass requires a robust trunnion assembly. It must be designed to be able to withstand all of the forces from the test system. Data Jianqiao can provide guidance and even design services for seismic isolation.

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Opto-Pneumatic Load Centering

The OPCS option for LE series shakers and the ALS option for some JQ series shakers both allow automatic centering of the armature using internal pneumatic support when the system is in the vertical position. This option helps to ensure that the shaker is in the center position for shock testing.  Additionally, this option is recommended if it is intended that a test article or head expander be left on the shaker when not in test. Otherwise, flexure warp can result over time. Users can always manually adjust the positioning.

Mobility Options for Electrodynamic Shakers

While it is almost always preferable to leave the electrodynamic shaker stationary, there are options available to easily reposition the shaker.

Combined thermal testing is a common application requiring mobile shakers. With larger shakers, however, it is still preferable to leave the shaker stationary and move the environmental chamber.

Historically, V-Groove wheels and rail guidance were used to move shakers under chambers. The guidance system placed the shaker in the center of the chamber in a repeatable fashion.

 Additionally, wheels or castors can be fitted to JQ series shakers for mobility.

Packaging and Shipment Preparation for Shaker Systems

All shakers require packaging and shipping preparation from the factory. In addition to the shaker system, head expanders, slip tables, and monobase slip table assemblies all require packaging to be added.

Inserts

Standard head expanders and slip tables will not have any threaded inserts in them. JIANQIAO allows flexibility in the insert pattern. Customers may choose a standard insert pattern, a custom insert pattern, or no insert pattern at all.

If adding a standard pattern, the pattern is centered and the inserts need to be purchased for the entire pattern. For instance, if it is a 9 x 9 pattern, 81 inserts need to be added. In some cases adding the shaker armature pattern to the slip plate is beneficial.

Specifying inserts also involves specifying thread size. On the same note, nearly every Signal Force shaker can be made with  metric threads, and that thread type has to be specified when ordering.

Thermal Barriers

It is generally recommended that thermal barriers be used on the shaker armature during any thermal testing, even if using a head expander and slip table. Armature thermal barriers are priced inclusive of any required raised inserts.

The barriers cover temperatures from -40° C to + 120°. Other materials are available for wider temperature ranges. These materials often require raised inserts in addition to the thermal barrier because they are made from softer silicon based material.

It is almost always recommended to have a separate thermal barrier for the head expander and slip plate due to the labor involved in switching them.

Bearing Guidance for Slip Tables

Any required guidance for a slip table is also separately specified. An overturning moment check will provide the information required to size the type and number of bearings needed for overturning moment restraint. Slip tables can be configured with standard linear bearings and hydrostatic bearings to restrain moments. Overturning moments will be discussed in more detail in next issue of the Insider.

Drive Adapter

Larger tests using slip tables should incorporate a drive adapter, sometimes referred to as a “bull nose”.  The general rules of thumb are to use a drive adapter on tests with masses greater than 100 lbs (45 kg) when a high restraint bearing system is used or if the force required is 18,000 lbf (80 kN) or higher. The article “When to Select an Optional Welded Magnesium Drive Adapter” reviews when to select a drive adapter.