COMBINATION PIEZOELECTRIC ACTUATOR AND SENSOR

Abstract

A test system includes a frame. A hydraulic actuator is mounted to the frame and is configured to support a test specimen. A piezoelectric actuator is configured to apply a force to the test specimen. A controller is configured to excite the piezoelectric actuator and provide an indication of force generated by the piezoelectric actuator by measurement of current or charge provided to the piezoelectric actuator.

Claims

1. A test system comprising: a frame a hydraulic actuator mounted to the frame configured to support a test specimen; a piezoelectric actuator configured to apply a force to the test specimen; and a controller configured to excite the piezoelectric actuator and provide an indication of force generated by piezoelectric actuator by measurement of current or charge provided to the piezoelectric actuator.

2. A test system comprising: a frame a hydraulic actuator mounted to the frame configured to support a test specimen, the hydraulic actuator having a movable element; an inertial mass coupled to the movable element to move therewith; a piezoelectric actuator mounted to the inertial mass on a side opposite the movable element, the piezoelectric actuator configured to apply a force to the test specimen; and a controller configured to control operation of the hydraulic actuator and excite the piezoelectric actuator.

3. The test system of claim 2 wherein the piezoelectric actuator provides an indication of force generated by piezoelectric actuator by measurement of current or charge provided to the piezoelectric actuator.

4. The test system of claim 1 wherein the piezoelectric actuator is connected in series with the hydraulic actuator.

5. The test system of claim 1 and a load cell configured to measure force applied to the test specimen.

6. The test system of claim 1 and a mass connected to a piston rod of the hydraulic actuator.

7. The test system of claim 6 and a load cell configured to connect to the test specimen on a side opposite of the hydraulic actuator.

8. The test specimen of claim 7 and a second mass configured to connect to the test specimen on a side opposite of the hydraulic actuator and a load cell connected to the second mass.

9. The test system of claim 1 wherein the controller is configured to operate the hydraulic actuator and piezoelectric actuator for test specimen testing at frequencies greater than about 1,000 Hz.

10. The test system of claim 1 wherein the controller is configured to operate the hydraulic actuator and piezoelectric actuator for test specimen testing at frequencies in a bandwidth of about 0.01 Hz to greater than about 1,000 Hz.

11. The test system of claim 1 wherein the controller is configured to operate the hydraulic actuator and piezoelectric actuator for test specimen testing at frequencies in a bandwidth of about 0.01 Hz to greater than about 2,000 Hz.

12. The test system of claim 1 wherein the controller is configured to operate the hydraulic actuator and piezoelectric actuator for test specimen testing at frequencies in a bandwidth of about 0.01 Hz to greater than about 3,000 Hz.

13. The test system of claim 1 wherein the frame comprises a base and two support columns supporting a crosshead over the base.

14. The test system of claim 13 wherein the hydraulic actuator is located in the crosshead.

15. The test system of claim 1 and further comprising an inertial mass coupled to a piston rod of the hydraulic actuator to move therewith, and wherein the piezoelectric actuator is mounted to the inertial mass, and wherein the piezoelectric actuator supports the test specimen on a side opposite the inertial mass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic representation of an exemplary testing machine.

[0012] FIG. 2 is a schematic representation of a controller of the testing machine of FIG. 1.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

[0013] Referring to the figures, an exemplary embodiment of a combination PE and hydraulic actuator system 10 is integrated into a typical servo-hydraulic testing system 11 such as the MTS 831.50, manufactured by MTS Systems Corporation of Eden Prairie, Minn. The test system 11 includes a frame 10 having herein a base 13 and two columns 15 that support a crosshead 17. Generally, the system 11 includes a hydraulic actuator 12 (herein mounted in the crosshead 17 by way of example) and a PE actuator 14. In this exemplary embodiment, an inertial mass 16 is attached to a piston rod 18 of the hydraulic actuator 12 to provide an inertial reaction for the PE actuator 14. The PE actuator 14 can be disposed in series between inertial mass 16 above a specimen under test (SUT) 22 and/or the PE actuator can be secured to the SUT 22 as shown in the FIG. 1 at 14′ on a side opposite the inertial mass 16 with an accelerometer 24′ in series with the PE actuator 14′ and the SUT 22. For the high frequency testing, the accelerometer(s) 14, 14′ can be used for a displacement estimation. Accelerometers 24, 24′ can be used to derive a relative acceleration hence relative displacement across the SUT 22 as described in United States Published Patent Application 2016/0202160, which is incorporated herein by reference in its entirety.

[0014] Since a PE transducer cannot measure to very low frequencies, another transducer such as a strain gage load cell 30 is provided. If desired, an accelerometer 26 can also be mounted to the load cell 30 and used for force transducer acceleration compensation as described in U.S. Pat. Nos. 7,331,209 or 9,658,122, which are incorporated herein by reference in their entirety.

[0015] The load cell transducer 30 can be located under the optional PE actuator/transducer 14′ which is under the SUT 22. In another embodiment, it may be desirable to include another inertial mass directly under the lower optional PE actuator/transducer 14′ in which case the load cell can be located 30′ and the inertial mass is then represented by reference 30. Or alternatively a delta P transducer can be used to measure fluid pressure on opposite side of the piston of the actuator 12 and the load cell can be removed entirely. It should be noted in yet another embodiment, multiple PE actuator/transducers can be used. For instance, both PE actuator/transducer 24 and 24′ can be used as illustrated. Likewise, multiple PE actuator/transducers can be used in series where indicated at 14 or 14′.

[0016] A controller 34 controls operation of the hydraulic actuator 12 and PE actuator/transducer 14. As is well known in the art, the controller 34 typically controls operation of the hydraulic actuator 12 by providing control signals to a servovalve 36 that in turn controls fluid flow to the hydraulic actuator 12. The controller 34 directly or indirectly through an interface module (actuator amplifier) excites the PE actuator(s) in the system 11. The current/charge delivered by the PE actuator motor amplifier to the PE actuator during test excitation is measured. In one embodiment, the current to each of the PE actuator/transducers 14, 14′ is measured by a current sensor, the signal of which is integrated over time so as to provide a total charge measurement. To avoid drift the current signal is provided to a high pass filter and then integrated. Then from this total charge measurement, the controller 34 estimate the force produced by the PE actuator from a believed linear relationship, although any nonlinearities can also be taken into account if present. The strain, which is proportional to displacement, can be ascertained by measuring the voltage applied to the PE actuators 14, 14′.

[0017] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.