Method and apparatus for controlled penetration drilling

• US 5,139,376 A
• Filed: 10/23/1991
• Issued: 08/18/1992
• Est. Priority Date: 10/23/1991
• Status: Expired due to Term

• Current Assignee: Excellon Automation Co.
• Original Assignee: Excellon Automation Co.
• Inventors: Pumphrey, Dennis M.
• Primary Examiner(s): Howell, Daniel W.
• Application Number:
  US07/780,881
• Time in Patent Office: 300 Days
• Field of Search: 408/1 R, 408/3, 408/13, 408/14, 408/15, 408/95, 408/98, 364/474.28, 364/474.35
• US Class Current: 408/1.00R
• CPC Class Codes: B23Q 3/002 Means to press a workpiece against a guide
• CPC Class Codes: B23Q 3/16 controlled in conjunction with the operation of the tool
• CPC Class Codes: G05B 19/4015 going to a reference at the beginning of machine cycle, e.g. for calibration
• CPC Class Codes: G05B 2219/45129 Boring, drilling
• CPC Class Codes: G05B 2219/49232 Limit penetration of drill into backup material, support
• CPC Class Codes: H05K 3/0044 Mechanical working of the substrate, e.g. drilling or punching H05K3/0008 takes precedence
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]
• CPC Class Codes: Y10T 408/03 Processes
• CPC Class Codes: Y10T 408/08 with means to regulate operation by use of templet, tape, card, or other replaceable information supply
• CPC Class Codes: Y10T 408/175 to control relative positioning of Tool and work
• CPC Class Codes: Y10T 408/20 Responsive to condition of work or product
• CPC Class Codes: Y10T 408/385 Rotatable about parallel axes
• CPC Class Codes: Y10T 408/5623 with presser foot

Abstract

A drilling machine and method of operation for drilling through holes in a workpiece while minimizing penetration of the drill tool into a back-up material which supports the workpiece. Before placing the workpiece on the machine, the vertical position of the back-up material is mapped. After selection of the drill site, the mapped position of the backup material proximate the drill site is retrieved. Using this information, a computer controller determines an absolute vertical position for a lower limit of the drill stroke. This lower limit is independent of the top of the workpiece or the thickness of the workpiece, thus eliminating the need to determine either of those values. The drill stroke is terminated once the drill tool reaches the lower limit, which is a nominal depth below the mapped position of the back-up material, insuring that a hole is completely drilled through the workpiece, while minimizing penetration of the back-up material. Also, vertical position sensors used for prior art depth control drilling can be used in the system disclosed.

Claims

1. 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, said spindle being adapted to cause rotation of said drill tool to effect drilling;

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 back-up material sensor device for sensing the vertical position of said top surface of said back-up material;

a storage device for storing data sensed by said back-up material sensor regarding the vertical position of said top surface of said back-up material;

a drill tool sensor device for sensing the vertical position of said drill tool; 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 storage device, so that said lower limit is at least as deep as the vertical position of the top surface of said back-up material, said control means minimizing drill penetration into said back-up material, while at the same time ensuring that said drill tool has completely drilled through said workpiece.

2. The drilling machine of claim 1, wherein said back-up material sensor device is mounted on said spindle.

3. The drilling machine of claim 2, wherein said back-up material sensor device comprises:

a pressure foot depending from said spindle, said pressure foot having a bottom surface which is adapted to engage said back-up material top surface, said pressure foot being movable relative to said spindle in vertical direction; and

a relative motion sensor which senses relative vertical motion between said spindle and said pressure foot.

4. The drilling machine of claim 3, wherein the back-up material sensor device is adapted to sense the vertical position of said top surface of said workpiece when said pressure foot is engaged with said back-up material and applying substantially the same downward force to said back-up material as during a drilling operation.

5. The drilling machine of claim 1, wherein said drill tool sensor device comprises:

means for sensing the absolute vertical position of said spindle; and

a pressure foot depending from said spindle, said pressure foot having a bottom surface which is adapted to engage a workpiece, said pressure foot being movable relative to said spindle in a vertical direction; and

a relative motion sensor which senses relative vertical motion between said spindle and said pressure foot.

6. The drilling machine of claim 5, wherein said drill tool sensor device further comprises means for sensing the position of a tip of said drill tool to accommodate for variations between a nominal position of said tool tip and an actual position of said tool tip.

7. The drilling machine of claim 6, wherein said tool tip position sensing means is adapted to determine the amount of offset between said tool tip from and said pressure foot bottom surface when relative motion between said pressure foot and said spindle commences.

8. The drilling machine of claim 1, wherein said means for controlling comprises a digital computer.

9. The drilling machine of claim 8, wherein said computer comprises said storage device.

10. The drilling machine of claim 1, wherein said back-up material sensor device is adapted to sense the vertical position of said back-up material top surface at a plurality of predetermined locations which form a grid.

11. 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.

12. The drilling machine of claim 11, further comprising means for sensing the vertical position of a tip of said drill tool to determine any variation between said nominal distance from said tool tip and said spindle compared to the actual distance from said spindle and said tool tip.

13. 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.

14. The method of claim 13, wherein the vertical position of the top surface of said back-up material is sensed prior to positioning a workpiece on said back-up material.

15. The method of claim 13, wherein the vertical position of the top surface of the back-up material is sensed at a plurality of locations on the back-up material, said locations forming a grid.

16. The method of claim 13, further comprises the steps of:

prior to conducting a drill stroke, sensing the actual vertical position of the tip of the drill tool; and

using said actual information regarding tool tip position in determining the absolute vertical position of the lower limit of a drill stroke.

17. 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.

18. The method of claim 17, wherein said mapping is performed while applying substantially the same force to said worktable as is applied during a drill stroke.

19. The method of claim 17, further comprises the steps of:

prior to conducting a drill stroke, sensing the actual vertical position of the tip of the drill tool; and

using said actual information regarding tool tip position in determining the absolute vertical position of the lower limit of a drill stroke.