GB2108658A - Optical perpendicularity measuring instrument - Google Patents

Abstract

An instrument for measuring the perpendicularity of deep holes with respect to the surface of a workpiece, contains a light source (14) at one end of a probe which shines light through an aperture (16) from where it is focussed by lens 24 onto a quadrature detector (26) at the opposite end of the probe. When the probe is inserted and centered in a hole, the deviation of the light beam from a zero point on the detector (26) is proportional to the deviation from perpendicularity of the hole. The detector can operate as a null sensing device when mounted on a movable table which is positioned by a servo feedback system. The position of the table is proportional to deviation from perpendicularity of the probe. The quadrature detector may comprise a square detector matrix, two linear matrices or a TV camera. <IMAGE>

Description

SPECIFICATION Optical perpendicularity measuring instrument The invention relates to optical measuring instruments and more particularly to such instruments used to measure the perpendicularity of the axis of deep holes drilled in a workpiece.

In certain manufacturing processes, a large number of deep holes must be drilled in a workpiece. For example, in the manufacture of a nuclear steam generator tube sheet, 10,000,1.8 cm diameter through holes are drilled in a forging having a thickness of 58 cm and a diameter of 3 m. These holes are drilled by long gun drills used on a numerically controlled horizontal gun drilling machine. The drills are initially guided by drill bushings. However, the thrust force applied in feeding the drill produces a buckling force such that the drill may wander off in any direction, influenced in some way by variations in material hardness and the initial entry angle. Such misalignment if not noticed will destroy the expensive workpiece.

It is therefore the principal objective of the present invention to provide an apparatus for continuously measuring the perpendicularity of the axis of these holes with respect to the surface plane of the workpiece so that the drilling machine could be stopped if it begins drilling nonperpendicular holes.

With this object in view, the present invention resides in an optical perpendicularity measuring instrument comprising a probe body having a light source supported therein and a target adapted to receive light from said light source and a lens for focusing the target light onto a quadrature detector, wherein said light source is disposed at one end of a tubular structure protruding from said instrument and the said lens are disposed adjacent the opposite end of said tubular structure, said target being normally disposed on the optical axis of said lens and the center of said quadrature detector, said quadrature detector producing an electrical signal proportional to the displacement of said target from said optical axis.

The apparatus can be easily adapted for incorporation into a numerically controlled drilling operation by providing a signal proportional to the perpendicularity of a hole. The signal can be used to control machine functions. This represents a major advantage of existing techniques of measuring the relative location of hole openings to determine perpendicularity. When the end of the probe body which contains the target is not laterally displaced, the image of the target will be in the centre of the quadrature detector to will indicate that no displacement has occurred.

The invention will become more readily apparent from the following description of a preferred embodiment thereof shown, by way of example only, in the accompanying drawings, wherein: Figure 1 is a cross-sectional view of an optical perpendicularity measuring instrument constructed in accordance with the present invention; Figure 2 is a plan view of photocell array quadrature detector for use in the instrument of Figure 1; Figure 3 is a side view of the expansion collet of the instrument of Figure 1; Figure 4 shows an alternate embodiment of a quadrature detection arrangement in accordance with the present invention; Figures 5A and 5B are plan views of the photocell arrays for use in the quadrature detector of Figure 4;; Figure 6 shows an embodiment of a quadrature detector which is used as a null sensing device in accordance with the present invention; and Figure 7 shows a mounting arrangement for attaching an optical perpendicularity measuring instrument to a gun drilling machine in accordance with the present invention.

Referring to the drawings in detail, Figure 1 is a cross-sectional view of an embodiment of an optical perpendicularity measuring instrument wherein instrument probe body includes an outer housing 10 and an inner tubular structure 12. A light source 14, such as a light emitting diode or incandescent lamp, is located at the leading end of the probe body and shines a beam of light through a target which comprises an aperture 16 in an opaque wall 18. In this embodiment, the target aperture 1 6 is filled with an optical fiber such that the aperture is uniformly illuminated and becomes the target image. Baffles 20 are disposed along the inner surface 22 of tubular structure 12, and serve to reduce light reflection along the structure.

Reflections are further reduced by coating inner surface 22 with a matt black finish.

After passing through target aperture 16, the beam of light bears the target image and is focused by an achromatic focusing lens 24 before being projected onto quadrature detector 26.

Quadrature detector 26 comprises a quadrature photocell or an array of photocells and produces an electrical signal in response to the beam of light striking its surface. This signal is transmitted to a signal processor 28. The signal processor provides an output through connector 30 which can be used to control machine functions or can be connected to a plotter, not shown, which records the deviation of the target image from the zero deviation point on the quadrature detector 26.

As the instrument is advanced into a hole which is to be tested for perpendicularity, compressed air is blown into port 32. This air passes along the length of the probe in a space between outer housing 10 and inner structure 12 and exists through slits in expansion collet 34. Any metal filings or other debris remaining from the previous drilling would be expelled by this air.

Prior to making a perpendicularity measurement, expansion collet 34 is expanded to contact the inner surface of the hole which has been cleaned by the compressed air. Uniform expansion of collet 34 acts to centre the probe in the hole. Various means of expanding collet 34 can be used within the scope of the invention. In this embodiment, a simple piston arrangement is used. Movement of pistons 36 toward the leading end of the probe body forces outer housing 10 to move with respect to inner structure 12. This causes the ends of collet 34 to strike angular surface 38, thereby forcing collet 34 to expand radially. The collet makes contact with the inner surface of the hole being measured, thereby centering the end of the probe. Wheel 40 is provided in tip 42 to facilitate the insertion of the instrument into a hole which is to be measured.

Figure 2 is a plan view of a two-dimensional array detector 26 which comprises a two dimension array of photocells 44. In practice this array could bea 100 x 100 or 200 x 200 photodiode array integrated circuit chip. A circular spot of light 46, corresponding to a circular target aperture, is shown in the center of detector 26.

Figure 3 is a side view of collet 34 used on the instrument of Figure 1. Slits 44 are provided along the collet to allow for the escape of compressed air which cleans the hold being measured. These slits also allow for the expansion of collet 34.

Figure 4 shows an alternate embodiment of a quadrature detector arrangement in accordance with the present invention. A beam of light containing the target image in the form of a square passes through achromatic focusing lens 24 and enters beam splitter 48. There the image is split into two beams and transmitted to two linear diode arrays 50 and 52, such as 1 x 1024 diode arrays. These arrays are used to detect beam displacement along the X and Y axes.

Figures 5A and 5B show a light beam 54 which corresponds to a square target aperture, shining on diode arrays 50 and 52. This arrangement would provide better resolution than the 200 x 200 photodiode array as in Figure 2, and the cost should be lower.

Figure 6 shows an embodiment of a quadrature detector arrangement in which the detector is used as a null sensing device. In this embodiment, a light beam containing a circular target image passes through focusing lens 24 before being reflected by mirror 56 onto quadrature detector 26. The detector 26 is mounted on a two axis micropositioning table 60 which is driven by two micromotors, not shown. Using known technology, these two motors are driven by two position servo loops with position feedback sensing provided by a quadrature detector 26, such as a quadrature photocell. The servo loops seek a null point at all times, and the displacements of the two axes are detected by shaft encoders, optical gratings, or linear sensors such as linear variable differential transformers.

Alternatively, the micromotors could be stepping motors, in which case displacement along the axes could be measured by counting the number of stepping pulses. In either case, the position of table 60 is directly proportional to the displacement of the target.

In operation, the probe is mounted on a gun drilling machine with an axial feeding mechanism.

The optical axis of the probe is aligned with the feeding axis and the probe is fed into the hole. An expansion collet sleeve located on the exterior surface of the probe is pushed forward by an actuator, which may be a simple piston. The collet expands, centering the target with respect to the inner wall of the hole. The target displacement with respect to the optical axis is measured by the quadrature detector. This process is repeated at several points along the length of the hole, to plot an alignment profile.

During the insertion of the probe, compressed air is forced into a cleaning jet inlet and is blown through slits in the expanding collet. This clears the hole of all metal chips and debris before the collet is actuated, centering the target with respect to the clean inner wall of the hole.

In an automated drilling system, the perpendicularity measuring instrument is provided with means for feeding it axially into a hole to be measured. A calibration block may be permanently mounted to the gun drill work mounting table, for periodic calibration of the instrument. Automatic data logging is possible by connecting the instrument to a low cost printer. A microcomputer can receive signals from the instrument for data collection and alarm monitoring.

Figure 7 shows a mounting arrangement for attaching an optical perpendicularity measuring instrument to a gun drilling machine in accordance with the present invention. Air cylinder 62 provides means for feeding probe 64 into a hole to be measured. Shaft 68 is attached to gun drill assembly 70 and passes through instrument case 72 to provide a means for aligning probe 64 with a hole to be measured. The optical axis of probe 64 is aligned parallel to the feeding axis of drill 74 to within +0.0064 mm and is mounted perpendicular to the X-Y plane of the workpiece.

The offset difference along the X axis between probe 64 and drill 74 is accurately measured and can be programmed into the machine control for automatic perpendicularity measurement.

Variations of this mounting arrangement can occur within the scope of this invention. For example, a motorized lead screw could serve as means for feeding probe 64 or a dove-tailed machine slide could provide means for aligning probe 64. Since the invention is a low-cost device, multiple probes could be mounted on a single gun drilling machine to provide simultaneous perpendicularity measurements.

It should be apparent to those skilled in the art that certain variations in the structure of an optical perpendicularity measuring instrument are possible within the scope of this invention. For example, commercial devices such as television cameras could be used as the quadrature detecting element. In addition, the signal processing function can be accomplished by external circuitry. It is therefore intended that the appended claims cover all such changes that fall within the scope of the invention.

Claims (10)

1. An optical perpendicularity measuring instrument comprising a probe body having a light source (14) supported therein and a target (16) adapted to receive light from said light source (14) and a lens (24) for focusing the target light onto a quadrature detector (26) said light source (14) is disposed at one end of the tubular structure (12) protruding from said instrument and the said lens (24) is disposed adjacent the opposite end of said tubular structure (12), said target (16) being normally disposed on the optical axis of said lens (24) and the center of said quadrature detector (26), said quadrature detector (26) producing an electrical signal proportional to the displacement of said target (16) from said optical axis.

2. An optical perpendicularity measuring instrument as claimed in claim 1, characterized in that a housing (10) carrying an expansion collet (34) surrounds said tubular structure (12) and means (36, 10) are provided for enlarging the diameter of said expansion collect (34) for centering said tubular structure (12) in a hole for which perpendicularity is being measured.

3. An optical perpendicularity measuring instrument as claimed in claim 2, characterized in that compressed air ports (32) are provided for the introduction of compressed air into the space between said tubular structure (12) and said housing (10) and openings (44) are formed in said expansion collet (34) permitting the expulsion of said compressed air.

4. An optical perpendicularity measuring instrument as claimed in claim 1,2 or 3, said light source (14) is a light emitting diode.

5. An optical perpendicularity measuring instrument as claimed in any of claims 1 to 4, characterised in that said target is an aperture (16) in an opaque wall (18) disposed adjacent said light source (14).

6. An optical perpendicularity measuring instrument as claimed in any of claims 1 to 5, characterized in that said quadrature detector (26) is a two-dimensional array of photocells.

7. An optical perpendicularity measuring instrument as recited in claim 6, characterized in that a signal processor (28) is associated with said quadrature detector (26) so as to be responsive to a signal produced by light striking said quadrature detector (26) for calculating the displacement of said target (1 6) from said optical axis.

8. An optical perpendicularity measuring instrument as recited in any of claims 1 to 5, characterized in that a beam splitter is arranged in the path of light from said lens (24) and adapted to produce two images of said target (16) that said target (16) is a square aperture and that said quadrature detector includes two linear photocell arrays (50, 52) so as to receive one of said images and being oriented in opposite senses.

9. An optical perpendicularity measuring instrument as recited in claim 1, characterized in that said quadrature detector (26) is mounted on a two-axis micropositioning table, means are provided for moving said micropositioning table to minimize a signal output from said quadrature detector, and means for measuring the displacement of said micropositioning table.

10. An optical perpendicularity measuring instrument as claimed in any of claims 1 to 9, characterized in that an optical fiber is disposed within said target opening (16).