Miniature Centrifugal Compressor Development

• Kevin Finney• Ray Zhou• Dr. Kapat• Dr. Chow

October 18, 2002

Current Status• Motor

– Problems encountered while building motor– Expected delivery date moved back

• Compressor Parts– Parts without blades, machined– Parts with blades, still working on CNC code

• Assembly of Compressor– Mounting of bearings– Design of jig fixtures

• Assembly Brackets– Use of shims or stage to align?– Cost of accurate alignment the first time, or chance of

failure and remanufacturing of parts?

Motor Update

• Problems with the carbon fiber winding– The carbon fiber winding was out of round,

and created a large unbalance. It had to be sent out to rewrap the fibers.

– Once it returns to Koford Engineering, the motor will be assembled and run at 150,000 rpm with no load.

• Will be delivered after winding problem fixed

Compressor Parts

• Problems generating code for CNC machine to run, has delayed first test

• Ironed out problems generating some of code

• More simple parts are machined (parts without blades), leaving the parts with the blades for last

Compressor Assembly

• Placement of Bearings– Use heat, for

expansion fit– Use force, for

interference fit• Design of Jig Fixtures

– Fixtures to hold part

– Fixture to press bearing (bushings)

• Press

Assembly Brackets

• Hold tight tolerances– Misalignment affected most by assembly of

components and mounting procedure– Tolerances add up, i.e. 0.002” shift in the

compressor to the left and 0.002” shift in the motor to the right = 0.004” misalignment

– More than likely, this 0.004” is absorbed in the bearings, and will cause overheating and abnormal wear characteristics.

– Misalignment Leads to Premature FAILURE!!!

Assembly Alignment• Adjust assembly alignment with shims or stages

– By using shims, becomes a tedious manual process, and adjustable only to 0.001”.

– By using a translational and rotational stage, the alignment may be adjustable to microns. The accuracy is determined by the tools used to measure the alignment.

• More accurate the alignment, more rigid the coupler can act

• Result of more accurate alignment means capable of higher speeds

Measuring Alignment of Assembly

• Faro Arm– Entire assembly mounted to common base, which will

be mobile– Construct cylinders by taking points on surface of

motor and compressor shaft, and measure the alignment of axes on the computer screen.

• If use a stage, the adjustment can be done quickly, and easily

• If use shims, the assembly has to be disassembled and reassembled, hoping to place near previous measurement

• Alignment Conclusion– Use stages to adjust in 5 degrees of freedom, if

affordable…(3 translation, 2 rotation)