Automated test hammer

1 . An automated test hammer apparatus, comprising:

an impact tip;

a bottom plate;

an enclosure;

a top plate;

an electronics cover;

magnetic clamps attached to the bottom plate such that they hold the bottom plate in position relative to a structure under test;

a group of magnets comprising:

an outer radial magnet ring polarized outward from the center,

an inner radial magnet ring polarized outward from the center,

an outer axial magnet ring polarized downward,

an inner axial magnet ring polarized upward;

a back-iron that supports the outer radial magnet ring, the inner radial magnet ring, the outer axial magnet ring, and the inner axial magnet ring, the back-iron completing the magnetic circuit between them;

a load cell connected to the impact tip and connected to the back-iron such that it transmits force from the back-iron to the impact tip;

shafts supported by the bottom plate and top plate;

linear bearings that slidably mount the back-iron to the shafts;

springs between the back-iron and the top plate;

a bobbin;

a coil wound around the bobbin residing in the annular space between inner rings and outer rings of the group of magnets; and

wherein current through the coil interacts with the magnetic field of the group of magnets creating an axial force by a Lorentz effect accelerating downward the back-iron, the outer radial magnet ring, the inner radial magnet ring, the outer axial magnet ring, the inner axial magnet ring, the load cell, and the impact tip.

2 . The automated test hammer apparatus of claim 1 , wherein impact of the impact tip against the structure under test creates a force pulse which is transmitted through the load cell and then to the structure under test, and wherein the load cell provides a measurement of the force pulse to an external data collection system.

3 . The automated test hammer apparatus of claim 2 , further comprising:

a power supply;

a capacitor;

a time delay relay;

a power relay;

a magnetic proximity switch; and

a start switch;

wherein the power supply applies DC voltage to the capacitor storing energy;

wherein toggling the start switch to the closed position applies DC voltage from the power supply to the time delay relay;

wherein, after a set time delay, the time delay relay starts to apply the DC voltage to the magnetic proximity switch;

wherein the magnetic proximity switch contacts are closed if it is in the magnetic field of the back-iron;

wherein the magnetic proximity switch applies the DC voltage from the start switch to the power relay if its contacts are closed.

4 . The automated test hammer apparatus of claim 3 ,

wherein when the power relay receives the DC voltage it conducts current from the capacitor to the coil, discharging the stored energy into the coil;

wherein the magnetic proximity switch contacts open when it is no longer in the magnetic field of the back-iron removing voltage from the power relay, thereby stopping current flow through the coil;

wherein stopping current flow through the coil stops the Lorentz force production in the coil;

wherein the springs between the back-iron and the top plate return the back-iron and connected components to a ready position when coil force production stops; and

wherein the capacitor discharge and force production cycle repeats automatically as long as the start switch contacts are closed.

5 . The automated test hammer apparatus of claim 4 , further comprising:

isolation washers between the bottom plate and magnetic clamps;

wherein the isolation washers allow small angular and positional relative motion to accommodate the structure under test when curved or irregular to reduce unwanted force transmission between the bottom plate and the test structure.

6 . The automated test hammer apparatus of claim 4 , further comprising:

a bleed resistor in parallel with the capacitor;

wherein the bleed resistor gradually discharges the capacitor for personnel safety when the power source is turned off.

7 . The automated test hammer apparatus of claim 4 , further comprising:

a flyback diode in parallel with the coil;

wherein the flyback diode allows current to continue flowing through the coil until an inductively stored energy is dissipated to reduce a voltage surge on the power relay.

8 . The automated test hammer apparatus of claim 4 , wherein the power supply is adjustable to vary the energy stored in the capacitor and thereby the magnitude of the force pulse.

9 . The automated test hammer apparatus of claim 4 , wherein the time delay relay is adjustable to vary the force pulse repetition rate.

10 . The automated test hammer apparatus of claim 4 , wherein the magnetic proximity switch is adjustable such that a distance that it extends into the back iron may be changed to vary when the power relay is turned off to stop current flow, such that the current is turned off just before impact.

11 . The automated test hammer apparatus of claim 2 , further comprising:

heat conducting bolts which pass through the bobbin to contact the coil and which attach the bobbin to the top plate;

wherein the heat conducting bolts transfer heat from the coil to the top plate.

12 . The automated test hammer apparatus of claim 2 , further comprising:

bumper springs between the back-iron and top plate;

wherein the bumper spring bring the back-iron to a gradual stop at the ready position.

13 . The automated test hammer apparatus of claim 2 , wherein the impact tip is replaceable to allow tailoring of the impact pulse frequency content.

14 . The automated test hammer apparatus of claim 2 , wherein the bottom plate, the enclosure, the top plate, and the electronics cover form a Faraday shield to prevent external electromagnetic radiation.