Gauging apparatus and method

• US 5,000,037 A
• Filed: 11/30/1989
• Issued: 03/19/1991
• Est. Priority Date: 11/30/1989
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Baresh, Joseph M.
• Primary Examiner(s): Raevis, Robert R.
• Application Number:
  US07/443,902
• Time in Patent Office: 474 Days
• Field of Search: 73/104, 73/865.8, 73/865.9, 73/1 J, 33/542, 33/544, 33/551-555, 33/501.02-501.04, 33/702, 33/712, 33/783, 33/787, 33/788, 33/807, 33/827, 33/DIG. 13
• US Class Current: 73/104
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: G01B 7/18 using change in resistance

Abstract

Disclosed is an apparatus and method for gauging the amount of warpage in a composite panel. In the gauging operation, elongate spacer strips (18) of uniform thickness are placed on the layup surface (14) of a mold (12) to support a panel (10) spaced apart from the mold layup surface (14) by a gap (22) of dimension equal to the thickness of the spacer strips (18). A sensor wand (26) that includes a strain gauge sensor assembly (32) is inserted in the gap (22) to detect and measure gap variations. Instrumentation (66,68) is utilized to operate strain gauges (52) that are included in the strain gauge sensor assembly (32) as a conventional bridge circuit. Measurement error caused by twisting and tilting of sensor wand (26) is minimized by smoothly contoured contact protrusions (54) of the strain gauge sensor assembly (32) that bear against panel surface (16) and layup surface (14). The width of sensor wand (26) and the mounting location of the strain gauge sensor assembly (32) also are established to minimize measurement error caused by twisting and tilting of sensor wand (26). Also included is a calibration fixture (70) for determining the relationship between electrical signals supplied by strain gauges (52) and gap dimension so that variations in gap dimension and hence the contour of panel surface (16) can accurately be determined.

Claims

1. A sensor wand for measuring dimensional variations in a gap of predetermined nominal gap dimension, said sensor wand comprising:

an elongate wand member having a first and second surface and a thickness that is less than said predetermined nominal gap dimension;

a strain gauge sensor assembly that is mounted near one end of said wand member, said strain gauge sensor assembly including first and second leaf spring members, the first end of said first and second leaf spring members being mounted to said wand member to maintain a fixed orientation relative to said first and second surfaces of said wand member, said first leaf spring member extending angularly away from one of said first surface of said wand member to position the second end of said first leaf spring member away from said first surface of said wand member, said second leaf spring member extending angularly away from said second surface of said wand member to position the second end of said second spring member away from said second surface of said wand member, each said first and second leaf spring member including an outwardly extending contact protrusion for bearing against one of the surfaces that define said gap to be measured, the region of each said contact protrusion that bears against said surface being contoured to control deflection of said first and second leaf spring members as a result of said wand member being rotated about its longitudinal centerline, said first leaf spring member further including a first strain gauge mounted thereon to sense deflection of said second end of said first leaf spring member toward and away from said first surface of said wand member, said second leaf spring member further including a second strain gauge mounted thereon for sensing deflection of said second end of said second leaf spring member toward and away from said second surface of said sensor wand; and

electrical connections for electrically connecting said first and second strain gauges to instrumentation for supplying an electrical signal to said first and second strain gauges and for receiving an electrical signal supplied by said first and second strain gauges.

2. The sensor wand of claim 1 wherein said contoured regions of both said first and second contact protrusions are of substantially hemispherical geometry.

3. The sensor wand of claim 1 wherein the region adjacent said first end of said first leaf spring member is relatively flat and said first leaf spring member is mounted to said wand member to maintain said relatively flat region substantially parallel with said longitudinal centerline of said elongate wand;

and wherein the region adjacent said first end of said second leaf spring member is relatively flat and is joined to said relatively flat region of said first leaf spring member to symmetrically position said first and second leaf spring members relative to one another.

4. The sensor wand of claim 3 wherein said relatively flat region of said first leaf spring member includes a centrally located cutout region that is positioned below said first end of said second leaf spring member to equalize the deflection characteristics of said first and second leaf spring members.

5. The sensor wand of claim 4 wherein said contoured regions of both said first and second contact protrusions are of substantially hemispherical geometry.

6. The sensor wand of claim 5 wherein said wand member includes a cutout region extending between said first and second surfaces of said wand member with said strain gauge sensor assembly being mounted in said cutout region;

and, wherein the distance between the end of said wand member nearest said strain gauge sensor assembly and said region of said contact protrusions that bears against said surfaces is established to further control deflection of said first and second leaf spring members as a result of said wand member being rotated about its longitudinal centerline.

7. The sensor wand of claim 6 wherein the width of said wand member is established to further control deflection of said first and second leaf spring members as a result of said wand member being rotated about its longitudinal centerline.

8. Apparatus for gauging differences between the shape of a part and the shape of a mold upon which the part was formed, said apparatus comprising:

a plurality of elongate relatively flexible spacer strips, each having a predetermined thickness, said elongate relatively flexible strips being placeable on the molding surface of said mold in spaced-apart relationship with one another to support said part in spaced-apart juxtaposition with regions of said mold that formed said part and form a gap between said part and said mold that has a dimension substantially equal to said predetermined thickness of said spacer strips; and

an elongate relatively flexible sensor wand dimensioned for insertion in said gap formed between said part and said molding surface, said sensor wand including a pair of leaf springs with each leaf spring being mounted near one end of said wand and extending angularly away from one another and outwardly from said sensor wand, each said leaf spring including a contact protrusion with one of said contact protrusions bearing against said part and the other of said contact protrusions bearing against said molding surface when said sensor wand is inserted in said gap between said part and said molding surface, said pair of leaf springs and said contact protrusions being dimensioned to deflect said leaf springs toward one another when said sensor wand is inserted in said gap, said sensor wand further including first and second pairs of strain gauges with one of said pairs of strain gauges being mounted to a first one of said leaf springs to sense deflection of said first leaf spring as said sensor wand is moved to various locations within said gap, the second one of said pairs of strain gauges being mounted to the second leaf spring of said pair of leaf springs to sense deflection of said second leaf spring as said sensor wand is moved to various locations within said gap, said sensor wand further including electrical conductors for interconnecting said first and second strain gauge pairs with instrumentation for supplying electrical signals to said strain gauges and receiving electrical signals from said strain gauges.

9. The apparatus of claim 8, further comprising a calibration fixture having a passageway dimensioned for insertion of said sensor wand, said passageway including a series of stepped regions with each said stepped region exhibiting a gap dimension that is within the gauging range of said sensor wand.

10. The apparatus of claim 8 wherein the width of said sensor wand substantially exceeds said predetermined thickness of said spacer strips to limit rotation of said sensor wand within said gap formed between said part and said mold.

11. The apparatus of claim 10 wherein each said contact protrusion is smoothly contoured to substantially eliminate deflection of said leaf springs toward one another when said sensor wand is rotated with said gap formed between said part and said mold.

12. The apparatus of claim 11 wherein each said contact protrusion is substantially hemispherical and exhibits a radius that is not less than one-half predetermined thickness of said spacer strips.

13. A method for gauging differences between the surface contour of a part and the surface of a mold upon which the part was formed to establish said surface contour, said method comprising the steps of:

supporting said part in spaced apart juxtaposition with said mold to form a gap of predetermined nominal dimension between said contoured surface of said part and said surface of said mold that established said contoured surface;

inserting into said gap a flexible sensor wand having outwardly extending first and second strain gauge equipped leaf springs that respectively contact said contoured surface of said part and said surface of said mold that established said contoured surface, said leaf springs being deflected inwardly to vary the resistive value of said strain gauges in accordance with the exact dimension of said gap;

energizing said strain gauges with an electrical signal to facilitate production of an electrical signal that is representative of said exact dimension of said gap;

urging said sensor wand through said gap; and

monitoring said electrical signal representative of said exact dimension of said gap as said sensor wand is urged through said gap to detect differences between said predetermined nominal dimension of said gap and said exact dimension of said gap.

14. The method of claim 13 further comprising the step of calibrating said sensor wand prior to said step of inserting said sensor wand in said gap, said step of calibrating including the steps of sequentially deflecting said first and second leaf springs to a plurality of positions that correspond to gap dimensions that are within a predetermined range of gap dimensions, and for each said position of said leaf springs determining the value of said signal representative of said exact gap dimension.