DSM Completes Phase I Design of Non-magnetic Piezoelectric Actuation System; Starts Phase II Program

An increasing number of actuation system applications require non-magnetic operation.  A recent SBIR Phase I program challenged DSM to design a piezoelectric actuator with a magnetic field level below that of the earth at a distance of 1 inch.  The strength of earth’s magnetic field at the surface ranges from 30-60 microteslas (300-600 milligauss).  At a distance of 1 inch DSM’s FlexFrame PiezoActuator™ FPA-1200, operating at 25Hz over its full 1.2mm stroke, had a magnetic field of < 1 µT (10mG) (This is within the noise floor of the sensor.)  DSM’s VF-90 electronics tested at < 2 µT (20mG) during actuator operation at a distance of 1” from its highest field part.  Electronics with an even lower magnetic signature are currently in development.  A custom DSM circuit, based on the HMC1053 magnetometer, was used for magnetic field sensing.

DSM completes installation of Vertical Linear Accelerator (VLA) at Wright-Patterson AFB; Dayton, Ohio

DSM completed installation of the vertical linear accelerator (VLA) at Wright-Patterson AFB Dayton, Ohio. 

(DSM's VLA page)

Abnormal visual-vestibular responses among aviation personnel may predispose them to spatial disorientation, loss of dynamic visual acuity, or airsickness.  Past pilot referrals to the Naval Medical Research Laboratory (NAMRL) from the Naval Aerospace and Naval Operational Medicine Institutes (NAMI/NOMI) have revealed that certain pilots may be predisposed to experiencing spatial disorientation, but whose deficiencies were only detected via specialized experimental acceleration equipment and tests. 

DSM’s new Vertical Linear Accelerator (VLA) was developed for NAMRL to meet two main clinical needs of the Navy: 1) to identify and transition suitable future visual-vestibular testing devices; 2) to identify and transition airsickness tests and desensitization protocols.  Particular emphasis is placed on vertical linear oscillation stimuli to the otolith organs, which sense the kinds of oscillations common during challenging aviation or sea operations and which are less well understood than the semicircular canals.

The VLA system has a stroke of 12 feet (3.66m) total and the capability to reach 1 G (2g total force with gravity) acceleration and a maximum velocity of 14 ft/s.  In order to maximize the value of the device to the NAMRL and the greater research community, the goal of the machine development is to make the device as smooth and as quiet as possible.  This is accomplished in part by the use of brushless linear motors and air bearings as the primary mover and guidance components.  The VLA will include an integrated dynamic visual acuity (DVA) tester and capability to run arbitrary waveforms.  Also included is the use of a triple redundant safety scheme utilizing long travel impact bumpers, rail brakes and regenerative dynamic braking. 

(From: http://www.flightglobal.com/articles/2010/12/07/350498/aeromedical-simulators-probing-the-weakest-link.html )
“There is the vertical linear accelerator, a device that oscillates pilots at two cycles per second (2Hz) like a salt shaker…”

“The US Navy says its new vertical linear accelerator, built with government small businesses innovation research funds, is complete and being installed at Dayton. The device has a chair with a display screen that travels up and down a 3.66m-long I-beam to study vertical motion environments, for instance in helicopter research. The chair can move at rates of up to 2Hz, exerting up to 2g of force on the subject. "A lot of the research is for helicopters and then some very specific things we might want to look at," says Simmons, adding that the device could be used to study visual/vestibular interactions for any vehicles "with vertical motion" - the F-35 VSTOL variant, for example.”

Phase II SBIR Results - Piezo Motors Ready for Your Application

DSM is a proud participant in the United States' Small Business Innovative Research (SBIR) program.   As a small US based company, we are able to employ a highly specialized technical staff whose main goal is to create new technologies to solve needs of organizations of the US Government. 

As a result of this activity, DSM has developed a team that can create products for you quickly based on the same design principles used for advanced technology projects. 

Below are just a few videos from our more recent piezo motor projects.

 VACCO valve using DSM's High Force Piezo Motor

Early DSM Piezo Motors

DSM provides design services and support to a wide audience.   Over the years we have created dozens of different prototypes.   Much of of DSM's work is proprietary in nature and cannot be shared.  However, we thought our readers might enjoy seeing some of the earliest and most basic DSM motor designs.  The following are from the early 1990s.  Enjoy. 

DSM Conducts Extensive Cryogenic Testing on Piezo Stacks from Multiple Vendors

DSM conducted four rounds of cryogenic testing on piezo-ceramic (PZT) stacks.   The tests were completed as part of ongoing piezo actuation system product development efforts for DSM's Small Business Innovative Research (SBIR) programs.  The test plan and results are available for purchase for $950.   The PZT vendors are not identified in the report.

Many PZT fabricators claim that multilayer stacks can be used at cryogenic temperatures.  DSM tested multiple vendor's PZT stacks under varying cryogenic conditions.  Driving the stacks with relatively high frequency oscillations appears to be particularly harmful.  In order to offer piezo-actuators and piezo-motors that can operate at very low temperature, DSM has been investigating combinations of stack construction, lead attachment technique, and coating that will demonstrate reliable operation from room temperature down to cryogenic temperature. 

Test Summary:

DSM Meets Project Milestone - Full Length Run, Vertical Linear Accelerator

This week DSM met a significant milestone on our SBIR Phase II "Vertical Linear Accerlerator" project. 

FULL LENGTH RUN!

DSM welcomes inquiries into this developing technology and is actively seeking commercial opportunities for this system and/or expansion into additional military platforms.

PROJECT DESCRIPTION:

A Phase II SBIR from the NAVY to design and build a Vertical Linear Accelerator for Human Visual-Vestibular Acuity Testing and Training.

Main Goal: To provide vertical linear oscillation stimuli to the otolith organs, which are apparently less well understood than the semicircular canals.
Motion Quality: Device must be as smooth and as quiet as possible to provide isolated stimulus to the saccule. This is accomplished in part by the use of brushless linear motors and air bearings as the primary mover and guidance components. 
Motion Requirements:  12ft. stroke, 2Hz freq. response, 1G peak acceleration, 182kg total payload, ± 3mm position error, arbitrary waveform capability.
DVA Test: The VLA will include an integrated dynamic visual acuity (DVA) tester.
Safety System:  To ensure that an uncontrolled fall does not occur, a triple redundant safety scheme utilizing long travel impact bumpers, rail brakes, and dynamic braking is being implemented. 
Completion: DSM plans to have the VLA completed Spring 2011

Driving a Spring Load with a Piezoelectric Actuator

When a piezo-actuator (whether amplified or non-amplified) is actuated against a spring load, it converts electrical energy into both motion and force.  This force will vary according to the amount of expansion/contraction achieved by the piezo-actuator under the applied electrical field.  When activated with an applied electric field, the piezo-actuator moves against the spring load until it reaches a force balance condition.  If at this point the spring load were to be removed, the stored potential energy within the piezo-actuator would be converted completely into additional motion.  Therefore, when working against a spring load, the amount of displacement that the piezo-actuator can produce in the spring load is less than the piezo-actuator’s free zero-load displacement.   The amount of displacement that the spring can be compressed or stretched is a function of the spring stiffness and the piezo-actuator stiffness. 

Click to see .pdf with formulas included

Piezo Actuators - Mounting and Handling Guidelines

(.pdf version here)

Improper use includes the following but is not limited to applications such as the following :

• DO NOT: introduce static compressive loads exceeding an actuator’s blocked force rating
• DO NOT: cycle the actuator beyond 80% of the first natural frequency of the mass loaded condition
• DO NOT: introduce loading conditions that create bending moments in the actuator’s frame
• DO NOT: introduce lateral or transverse loading of the actuator’s output pad or mounting point that exceeds 5% of the actuator’s force rating

Proper Uses

Amplified piezoelectric actuators may be loaded only through their output plates in the direction co-axial with the output displacement. All loading must be applied uniformly and axially through the mechanism. The applied forces must be centered very well on the mounting face.

Tilting and shearing loads must be avoided or else they will damage the actuator. Lateral or transverse loads and bending loads may cause damage to the actuator ceramics and frame.  Lack of parallelism between mounting faces can be a principal cause of actuator failure.  This type of failure can be prevented by using ball tips, flexible tips, adequate guiding mechanisms etc.

 

Appropriate loading direction for an FPA

This limitation applies to both static and dynamic loading and any combination of the two.  Care should be applied to verify that any dynamic loading (operating at high frequency with an attached mass) does not exceed the recommended load.

The flat output surfaces of the actuator should be mounted to a precision flat and smooth-ground, non-rotating surface.  The FPA actuator should not be expected to carry moments and transverse forces.  Supplemental guidance like bearings or flexures should be used if loads greater than 5% of the product of the actuator stiffness and stroke must be supported.

Avoid Applied or Reaction Moments to the Output of the FPA Piezoelectric Actuator

X-axis, Y-axis, and Z-axis moments if applied to the output plate of the FPA can cause damage to the guiding actuator flexures.  Mis-alignments between the mounting surface and the moving surface can lead to failures during mounting and electrical operation of the actuator.  If a moment remains on the mounting surface when the actuator is energized, the moment applies an additive stress to the actuator flexures and the piezoceramic.  The additional mounting stress can cause the stress in the actuator flexures to exceed the design stress. 

Use of a plain-faced mounting to the plain face of the actuator should only be attempted if a proper application analysis verifies that the X-axis and Z-axis moment loads are minimal.  Otherwise, use a spherical coupling or flexure hinges to decouple the moment loads from the actuator.  Consider having DSM analyze your mounting and loading conditions if you have questions about your application. 

Mounting Recommendations

1.       When attaching the actuator to a mounting surface, use a clamp or wrench to support the actuator output block while leaving the opposite end of the actuator free to prevent the Y-axis twisting moment from damaging the actuator.

2.       Use a spherical coupling or flexure coupling to prevent X-axis and Z-axis moments from damaging the actuator during electrical operation or actuator motion.

3.       Apply a linear guidance bearing to the moving output to carry any moment loads that may be present and to prevent them from damaging the actuator.

4.       If using adhesive to mount actuators, use ground surfaces. During curing, do not exceed the operational temperature range of the actuator.

5.       The environment of all actuators should be as dry as possible.  The combination of high electric DC fields and high relative humidity values should be avoided with all piezoelectric actuators.

6.       Because the piezoelectric ceramics in the actuator can develop a charge when handled and under temperature loading, it is important to keep the actuator leads short circuited during mounting and handling. 

7.       Piezo actuators are sensitive to moisture, high relative humidity, liquids and contact with any other electrically conductive materials.  Avoid operating actuators under these environmental conditions since they can cause dielectric breakdown. 

Actuator Force Output and Available Stroke

The magnitude of the applied load should not exceed the “blocked force” rating of the actuator.  The blocked force rating is a product of the stroke and the stiffness of the actuator. 

Example:

DSM’s FPA-0100E-S-0518-150-SS has a rated stiffness of 1.8 N/micron and a rated displacement of 100 microns over the standard –30 to +150V range.  Therefore, the maximum recommended load (block force) is 180 N for this model. 

DSM defines a piezo actuator's "blocked force" as being that force which is required to compress/extend a fully extended/contracted actuator back to its zero position.  In most cases, DSM designs the actuator's flexures such that the blocked force corresponds to the flexures' maximum design stress.  Even under a static load equal to an actuator's blocked force, the actuator will be able to move through its full range of motion and will respond rapidly to changes in the applied voltage field.  The static load simply shifts the actuator's static position.  An analogous situation is to think of the piezo actuator as a spring that has a static load placed upon it.  The static load compresses the spring (piezo) to a new static position.  Subsequent changes in temperature (voltage) cause the spring (piezo) to change dimensions.

Sample FPA Piezoelectric Actuator with Transverse Mounting Loads (Orange and Green) to Avoid

Isolating FPA and LFPA Piezo Actuators from Moment and Lateral Loading

(.pdf version here)

As described in the application note, “Piezo Actuators - Mounting and Handling Guidelines”, mounting hardware must not apply a moment or lateral loading to the output faces of the actuator frames.  If mounting conditions or loading may apply a moment or allow lateral motion, the user should apply isolation flexures or ball pivots to the actuator’s output faces or use supplementary bearing stages to carry the moments or lateral loads.

Simple Spherical Pivots

A example of a simple isolation method using hemisphere pivots is shown in Figure 1.  The wrapped around frame may be comprised of conventional hinge mechanisms or a flexure using a resilient material.  Spherical pivots can be full or hemispheres and may be captured in machined divots in the wrap around frame.

Figure 1 – Using Spherical Endcaps in a Flexure frame to isolate Piezo-Actuator from Lateral or Moment Loading

The follower frame can also be designed with a spring preload in order to carry any stretching load that might act to separate the frame from the Piezo-Actuator.  Figure 2 shows a different scheme for achieving the same purposes. 

Figure 2 – Using Spherical Endcaps in a Spring-loaded Follower Plate to Limit Moment and Lateral Loading

Simple Flexure Joints

A example of a simple flexure method for isolating the actuator using cross flexures is shown in Figure 3.  Another option is the use of conventional shaker stingers (like those on voice-coil shakers) on the actuator outputs. 

Figure 3 – Using Flexure Joints on the Output of the Actuator to Limit Moment and Lateral Loading

Naturally, when flexures, stingers or spherical joints are used, off axis loading will cause rotation of the unit.  External guidance (Figure 1) or external stages like ball or crossed roller stages will prevent such rotation. 

DSM can be contracted to design a suitable frame for your application.