Method and apparatus for controlled penetration drilling

A drilling machine in which the depth of a hole drilled completely through a workpiece can be precisely controlled to decrease drill wear and to improve the throughput of said drilling machine, said drilling machine comprising:

• a spindle movable at least in a vertical direction, a drill tool removably mounted in said spindle, a tip of said tool being positioned a nominal distance from the bottom of said spindle, said spindle being adapted to cause rotation of said drill tool to effect drilling;
• a vertical position sensor which senses the absolute vertical position of said spindle and drill tool;
• a worktable positioned beneath said spindle, said worktable adapted to have a workpiece mounted thereon, said worktable being movable in at least one direction in a horizontal plane so as position said workpiece at desired locations beneath said spindle;
• a back-up material having a top surface, said back-up mounted on top of said worktable with said top surface facing upwardly, toward said spindle so that workpieces mounted on said worktable are positioned directly in contact with said top surface of said back-up material;
• a pressure foot mounted on said spindle and movable in a vertical direction relative to said spindle, a bottom surface of said pressure foot adapted to engage a workpiece which is mounted on said worktable, said drill tool passing through an aperture in said pressure foot during drilling operations;
• a relative movement sensor which senses relative vertical movement between said spindle and said pressure foot, said relative movement sensor sensing movement of said pressure foot which occurs upon initial contact between said pressure foot bottom surface and a workpiece;
• a computer controller which controls operation of said drilling machine, and which receives input from said vertical position sensor and said relative movement sensor and said vertical position sensor, said controller comprising:
• a computer memory device for storing a map of data regarding the vertical position of said backup material top surface, said controller adapted to generate said data by engaging said pressure foot bottom surface directly with said back-up material top surface in a plurality of locations, said mapped data comprising, for each of said locations, the absolute vertical position of said spindle measured by said vertical position sensor at the point at which said relative movement sensor senses contact between said pressure foot bottom surface and said back-up material;
• and
• means for controlling the vertical displacement of said spindle during a drill stroke, said control means adapted to determine an absolute vertical position for said tool tip at a lower limit of a drill stroke and to terminate said drill stroke when said tool tip reaches said lower limit, said absolute vertical position being determined using the data regarding the vertical position of the back-up material top surface in said memory device, so that said lower limit is at least as deep as the vertical position of the top surface of said back-up material, so that drill penetration into said back-up material can be minimized, while at the same time ensuring that said drill tool has completely drilled through said workpiece, without requiring precise knowledge of the vertical position of the top of the workpiece or the thickness of the workpiece.

A method of drilling a workpiece on a drilling machine, said drilling machine having a spindle movable at least in a vertical direction, a drill tool removably mounted in said spindle, said spindle being adapted to cause rotation of said drill tool to effect drilling;

• a worktable positioned beneath said spindle on which a workpiece can be mounted;
• and a back-up material having a top surface, said back-up mounted on top of said worktable with said top surface facing upwardly, toward said spindle so that workpieces mounted on said worktable are positioned directly in contact with said top surface of said back-up material, said method comprising the steps of:
• sensing the vertical position of the back-up material top surface;
• storing the data sensed regarding the vertical position of the top surface of the back-up material;
• determining an absolute vertical position of the tool tip at a lower limit of a drill stroke, using the stored data regarding the vertical position of the back-up material top surface, so that the lower limit is a nominal distance below the back-up material top surface;
• initiating a drill stroke by downward vertical motion of said spindle;
• sensing the vertical position of the tip of the drill tool during the drill stroke;
• and
• terminating the drill stroke when said drill tool has reached said predetermined absolute vertical position so that drill penetration into said back-up material can be minimized, while at the same time ensuring that said drill tool has completely drilled through said workpiece.

A method of drilling a workpiece on a drilling machine, said drilling machine having a spindle movable at least in a vertical direction, a drill tool removably mounted in said spindle, said spindle being adapted to cause rotation of said drill tool to effect drilling;

• a worktable positioned beneath said spindle on which a workpiece can be mounted;
• and a back-up material having a top surface, said back-up mounted on top of said worktable with said top surface facing upwardly, toward said spindle so that workpieces mounted on said worktable are positioned directly in contact with said top surface of said back-up material, said method comprising the steps of:
• mapping the top surface of the back-up material before mounting a workpiece on the back-up material so as to determine the vertical position of a plurality of locations on the back-up material top surface;
• mounting a workpiece on the back-up material:
• positioning the worktable relative to the spindle to permit drilling at a desired drill site on the workpiece;
• determining an absolute vertical position of the tool tip at a lower limit of a drill stroke, using the mapped data regarding the vertical position of the back-up material top surface at a location on the back up material top surface proximate said drill site, said lower limit being set at a nominal distance below the back-up material top surface;
• initiating a drill stroke by downward vertical motion of said spindle;
• sensing the vertical position of the tip of the drill tool during the drill stroke;
• and
• terminating the drill stroke when said drill tool has reached said predetermined absolute vertical position, so that drill penetration into said back-up material can be minimized, while at the same time ensuring that said drill tool has completely drilled through said workpiece.