PPOD User Guide

6 DoF PPOD

This article outlines the setup and use of the 6 DoF PPOD for part manipulation and flexure testing, as well as analysis of flexure test results.

DAQ Info

PCI Cards

For all uses of the 6 DoF PPOD the computer should have the National Instruments PCI-6224 input DAQ card and the National Instruments PCI-6713 output DAQ card. The installed National Instruments DAQ cards can be checked using the MATLAB command:

daqhwinfo('nidaq')

Calling this with no argument outputs a structure with all of the available DAQ hardware:

daqhwinfo

DAQ Board

The output card connects to the lower left socket in the photo above. The input card has two ribbon cables that connect to the other two sockets along the bottom: the upper cable on the PCI card connects to the right socket (channels AI0:AI15) and the lower cable connects to the middle socket (channels AI16:AI31).

The ribbon cable socket along the right edge connects to the accelerometer/speaker board, providing power and accelerometer readings.

The D-Sub socket in the upper right corner is for the force sensor used in flexure testing experiments. The switches above the screw terminals should both be to the left.

The power socket is on the left edge with the power switch found directly below it. The six speaker outputs are found along the top with speaker 1 on the far left and speaker 6 on the right.

All screw terminals should be empty during normal use (with the exception of channels 16:17 and 24:25 which can be used at any time). The input channels can also be used to read in signals from the screw terminals found above the lower sockets. To read in from the screw terminals for channels 0:15, unplug the ribbon cable leading to the accelerometer board. To read channels 18:23, slide the right switch found above the screw terminals to the right. The same goes for channels 26:31 with the left switch.

Part Manipulation

For part manipulation the force sensor should be unplugged as it adds a small amount of noise to the other signals in the system.

Troubleshooting

If the PPOD is not performing properly, the following steps should followed to ensure everything is set up correctly.

Power

If the control/accleration signals are zero or the plate is having difficulty controlling then there may be a problem with the power. Ensure all of the amplifiers and the DAQ board are turned on and have power. Check to see if all the amplifiers are set to the same gain (+8 dB has been found to work well, though any value that will not overload the actuators should work).

Mechanical Connections

If one or two control signals are saturating, or the PPOD is rattling then there may be a problem with the mechanical connections. Manually inspect the flexures for signs of buckling, kinking, or misalignment. If necessary, replace damaged felxures using Tygon tubing and metal bonding epoxy. When changing flexures, sometimes it is necessary to rotate an actuator slightly to keep the flexure aligned. To do this, loosen the bolts found on the underside of the base below the desired actuator. Check the set screws on the plate and actuators that hold the flexures in place. Check the springs to make sure they are tensioned approximately evenly.

DAQ Initialization

If the PPOD will not function at all or the signals do not match the plate motions then there may be a problem with the DAQ initialization/setup in MATLAB. The BoardNames match up with the respective InstalledBoardIds in the output structure. If the PPOD does not work, ensure that the DAQ objects were initialized properly by comparing the 'DevX' from above with the handles.daqinfo.ai and handles.daqinfo.ao object in the Initializedaqinfo.m file, set in lines 25-26. Output channels should be 0:6 (0 is the clock pulse, 1:6 are speaker channels) set in line 36. Input channels should be 0:11 (for the 12 accelerometer signals) set in line 39.

Speaker/Accelerometer Connections

If one or more signals are zero, or the signals do not match the plate motions then there may be a problem with the speaker/accelerometer connections. Check the connections on the back on the amplifiers. CH 1 input corresponds to Channel A output, and CH 2 with Channel B. Ex. Channel 1 leading out from the DAQ board should connect to CH 1 of the bottom amplifier and the leading out of Channel A should connect to the screw terminal labeled Speaker 1 on the accelerometer board. Accelerometer 1 should be found above Speaker 1, Accelerometer 2 should be found above Speaker 2, etc on the PPOD. The pins on the accelerometers plug into the holes on the ribbon cable sockets that are closest to the end of the cable. Check the MATLAB function L2Wconverter.m to ensure that the accelerometer locations in the function correspond to the actual locations on the plate.

Other

These steps should solve most problems encountered during normal use of the PPOD. If problems persist, it may require a more in-depth examination of the code and/or physical setup.