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Browse Prior Art Database

Capacitive Top Reference Detection for Blind Hole Drilling Of Pc Panels

IP.com Disclosure Number: IPCOM000101411D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 109K

Publishing Venue

IBM

Related People

Kulesza, JD: AUTHOR [+3]

Abstract

Disclosed is a method of detecting capacitance variance in the air bearings of high speed, air-driven turbine, drilling spindles and relating this capacitance variance to top panel position which is used for drill length adjustment critical for accurate blind hole drilling.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Capacitive Top Reference Detection for Blind Hole Drilling Of Pc Panels

       Disclosed is a method of detecting capacitance variance
in the air bearings of high speed, air-driven turbine, drilling
spindles and relating this capacitance variance to top panel position
which is used for drill length adjustment critical for accurate blind
hole drilling.

      This method is primarily intended for use on the type of
drilling machine that references the top of the PC panel to the drill
in the vertical plane rather than the bottom and provides a means for
tracking the vertical position of the drill.

      A typical spindle/panel layout is shown in Figure 1 along with
physical representations of the electromechanical components.

      This method employs a special circuit shown in Figure 2 that
produces a change in output as the tip of the drill comes in contact
with the conductive top surface of the panel.

      A high frequency electrical sinusoid signal is impressed across
the spindle air bearings through an inductor.  A pure sine wave is
used to reduce the distortion caused by higher-order harmonics.  The
inductor and frequency are varied to match the natural impedance of
the air bearings when the drill is not in contact with the ground
potential of the panel's top surface.  This will produce a high "Q"
series resonant circuit with a center frequency near the roll-off
point of the natural impedance of the air-bearing capacitors.

      When the drill comes into contact with the panel, the guide
bearing capacitor is shorted out to ground and the thrust bearing
capacitor is left in parallel with the shim capacitor which changes
the net impedance of the circuit. This causes the center frequency of
the resonant circuit to shift higher.  The drive frequency (which
does not change) is attenuated by a lowering of the Q at that
frequency.  The attenuated signal then produces the top reference
detection signal.

      This signal is used to "freeze" the vertical position of the
drill, as indicated by a vertical position tracking device.
Depending on the type of vertical drive that moves the spindle and
drill, this frozen position will either be a cam angle, a linear
encoder count, or an analog voltage as from an LVDT.  In any case,
the frozen position will relate to a critical drill length dimension
which must be known in order to drill accurate blind...