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Variable Depth Blind Hole Drilling

IP.com Disclosure Number: IPCOM000101622D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 5 page(s) / 185K

Publishing Venue

IBM

Related People

Krzyzewski, AS: AUTHOR [+2]

Abstract

Disclosed is a means to achieve variable depth blind holes drilled into printed circuit boards. The process is insensitive to drill length variation, drill seating depth variation, drill diameter, hole depth, panel thickness variation, and panel composition.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 36% of the total text.

Variable Depth Blind Hole Drilling

       Disclosed is a means to achieve variable depth blind
holes drilled into printed circuit boards.  The process is
insensitive to drill length variation, drill seating depth variation,
drill diameter, hole depth, panel thickness variation, and panel
composition.

      The method employs a single microprocessor (MPU) per drilling
spindle with independent vertical (Z) servo drive and glass
incremental encoder feedback for tracking relative position of the
drill tip.  The drilling spindle also has a moveable pressure foot
which clamps the panel before drilling.  The pressure foot may be
dependent or independent of the spindle drive; however, the pressure
foot must precede the drill in vertical motion until the pressure
foot contacts the panel top.

      Key to this approach is an electrical contact which is fixed to
the Z servo that dimensionally references the top of the panel by
touching the clamped pressure foot in a "make contact" fashion or by
indicating cessation of concerted motion between drill and pressure
foot after pressure foot clamp in a "break contact" fashion.  In
either case, the top reference position is used by the MPU along with
a predetermined drill length compensation factor, and the hole depth,
to calculate the remaining distance required to reach the bottom of
the hole.  The variable position of the top of the panel relative to
the drill tip is determined before the drill tip touches the panel;
this feature gives the Z servo more time to respond to shallow hole
depths at higher infeed rates with less overshoot.

      The drill length compensation factor is a measurement of the
relative dimension between the contact point and the tip of the
drill.  This factor can vary with drill length or seating depth and
must be determined after each drill change.  Fig. 1 shows that this
method employs a gage station 1 which consists of a pressure foot pad
2 mounted at a fixed, known, vertical height; and a moveable drill
pad 3 mounted at the same height which has an incremental encoder 4
attached to it.  The spindle 5 is positioned over the gage station 1
and the spindle Z servo is moved to a vertical position which ensures
pressure foot 6 contact with the pressure foot pad 2 and that the
drill 9 contacts the drill pad 3 and moves the attached encoder 4.
The vertical repeatability of the top reference contact 8 can be
checked by comparing the contact position (as read from the spindle Z
encoder) with the known position of the pressure foot pad 2 height.
The drill length compensation factor is determined from the position
error, as read from the gage encoder 4, when the drill 9 is at a
position that would produce zero error on a drill with correct length
and seating depth.

      Note that the Z servo is in motion when the contact position is
read which could introduce contact repeatability error if the feed
rate is too high, but that the drill gage position is read...