Measurement of Modular Coil Keystone Effect Peer Review 4/1/03

Purpose The desired positional tolerance for location of the coil stack magnetic center is 1.5mm (0.060”). This is a the total allowable tolerance, and includes buildup of all tolerances (casting, machining, winding, impregnation, positioning/installation of coils. Measurement and incorporation of key-stoning effect is necessary to meet these tolerances Measure the keystone effect (deformation of the cross section) that occurs at the various radii bends. Develop a relationship between bend radius and keystone effect. Determine whether or not there is enough “give” to allow us to push the stack back into the desired geometry using the hold down clamps. Transfer this information to modular coil design/details.

Keystone Test Setup We have fabricated a full scale mock-up of half of the modular coil onto which we will wind conductor. We will use the actual conductor (4-bundle), and the tape it with the coil taping device We will measure the key-stoning fixture to establish a baseline. We also have the design drawings as a baseline. We will wind one layer, of at least 6-7 turns, clamping the conductor to the fixture and taking measurements during each turn.

Keystone test fixture

Measurement Options Can use global and/or local measurement system to obtain measurements. Global measurements taken with the FARO arm, which would be mounted directly on the key-stoning fixture. Local measurements will be taken with a set of measuring instruments designed specifically for this task. Precision of either measurement system is high. FARO measurements can be more precise, however processing the data is difficult. Local measurements yield immediate readout. Accuracy of measurements (using either system) depends on the accuracy of the fixture, which is not perfect.

Measuring tools Various versions of the local measuring tooling. This tooling is quickly and inexpensively fabricated. We can and will customize versions for the various geometries that we encounter. A simple version of this tooling is envisioned for use as the “go, no-go” gauge for winding the actual coils in the future. With dial indicator for direct reading With dial indicator and roller wheel for +/- reading With a spring loaded rod. Used like a tire tread depth gauge.

Data Desire to create a set of measurements that can be formatted into tabular form. We would establish a relationship between bend radius and keystone distortion. The global shape/contours of the fixture need not be determined, so long as we understand the local relationship between curvature and distortion. Will use the local measurements as the primary measurements and will take FARO arm data as a back-up. Will use the FARO arm to establish the the line created by the intersection of the two “walls” of the fixture. This will give us the bend radius. Will accurately mark the locations that the local measurements are taken so that they can be repeated.

Potential Difficulties To a great degree, some of the data will only be a good as the fixture. The fixture is not perfect. The relative position of the conductor to the fixture will be difficult to measure The conductor is wrapped with Kapton/fiberglass tape which is “spongy”. This could affect both precision and accuracy. The good thing is that we will be able to measure the “bundle” accurately. This is probably the most important measurement.