GB2025043A

GB2025043A - Measuring or Checking the Position of Holes in a Component

Info

Publication number: GB2025043A
Application number: GB7924770A
Authority: GB
Original assignee: Coventry City Council
Current assignee: Coventry City Council
Priority date: 1978-04-28
Filing date: 1979-07-17
Publication date: 1980-01-16
Also published as: GB2025043B

Abstract

A measuring head (1) contains a source (12, 13, 14) of parallel light and a plate (11) having a circular hole (110) therein. The head (1) further containing means such as electromagnetic force coil means (41, 42) for imparting circular vibratory motion to the plate (11). In use light from the plate hole (110) is arranged to pass through a hole (20) in a component (2) located in alignment (subject to any error) with the plate hole (110) and onto light responsive means (3) such as a photo-electric cell or photo- multiplier. If the circular hole in the plate 11 and the hole 20 in the component 2 are aligned the photocell 3 receives substantially constant illumination. In the event of variation of the light incident on the light responsive means (3) a resulting error signal is derived by a phase sensitive detector 32 and integrator 34 and 35. The outputs of the integrators may be fed to digital voltmeters 36 and 37 and/or be used in a servo-control system to align the circular hole 110 with the hole 20. <IMAGE>

Description

SPECIFICATION Hole Position Measurement The object of this invention is to provide improved apparatus for measuring or checking the position of a circular hole in a component or the like by means of an electro-optical system incorporating a vibration technique. A particular object is to provide such apparatus or units thereof of simple and compact form capable of rapidly carrying out hole position measuring or checking to a high degree of accuracy. Practical advantages in this respect will be apparent from the following disclosure.

According to this invention apparatus for measuring or checking the position of at least one hole in a component or the like comprises at least one unit or head containing a source of parallel light and a plate having a circular hole herein for passage of said light and capable of circular vibratory motion in its plane about a relatively small circle and with constant orientation for corresponding circular motion of the hole axis, means within the unit or head for imparting said circular vibratory motion to the plate, the unit or head having an opening or window for passage of the light from the plate hole through a hole or corresponding hole in a component or the like when located with said hole in alignment (subject to any error) with the plate hole and between the latter and light responsive means of the apparatus, the apparatus further including means responsive to an error signal from the light responsive means in the event of variation in the light incident thereon due to said vibration of the plate and mis-alignment of the component or like hole with the plate hole.

In practice the construction and arrangement may be as follows, reference being had to the accompanying drawings in which: Figure 1 is a sectional elevation of a unit or head of the apparatus shown in relation to a test piece.

Figure 2 is a block system diagram, and Figures 3 and 4 are elevation and plan views respectively of a force coil arrangement on an enlarged scale.

Referring to Figure 1 the apparatus can be mainly and compactly incorporated in a unit or head 1 which is mounted in relation to a circular hole 20 in a test piece 2. Where the test piece 2 has more than one hole in it requiring location measurement or checking, a further head or heads are provided each mounted for use in relation to a corresponding hole 20' as indicated at 1'.

Each head 1 consists of a housing 10 containing a lamp 12, a plate or mask 13 having a pin hole 130 in it and a lens 14 or lens system whereby a collimated beam L of parallel light can be provided for passing through a hole 1 10 in a vibratory plate 11 within the head 1 and through a clearance opening or window 100 in the lower end of the housing 10 and then through a corresponding hole 20 in the test piece 2 on to a photo-electric cell 3, e.g. a silicon photo-voltaic cell. However other suitable light responsive means may be employed such as a photomultiplier.

Preferably by means of electro-magnetic force coils indicated at 41,42 (Figure 2) as hereinafter described, the plate 11 is vibrated for circular motion in its plane about a relatively small circle and with constant orientation.

If the average position of the plate hole 110 and the position of the hole 20 in the test piece 2 are aligned, then despite the vibration of the plate 11, the light falling on the photo-electric cell 3 remains constant. However, if the said positions are mis-aligned, variation in the light falling on the photo-electric cell 3 occurs causing an alternating signal to be emitted form the photo-electric cell 3.

The phase of this signal in relation to the vibratory motion of the plate 11 depends on the direction of the mis-alignment.

Referring to Figure 2 the error signal from the photo-electric cell 3 is amplified at 31 of the system 30 and phase sensitive detected at 32 in two phases corresponding to the X and Y components of the error. This error signal may be processed to give a direct indication of the positional error involved or, preferably, the signal is used to move the vibratory plate 11 bodily until no alternating signal is received from the photoelectric cell 3. Such bodily movement of the vibratory plate 11 then indicates the error in the position or location of the hole 20 in the test piece 2.

In addition to reference phasing of the detector 32 the oscillator 33 operates the electromagnetic force coils 41, 42 ninety degrees out of phase so as to impart the required vibratory circular motion to the plate 11 itself.

The phase sensitive detected error signal from the photo-electric cell 3 is passed to integrators 34, 35 and from thence to the electro-magnetic force coils 41,42 for imparting bodily movement to the plate 11 for effecting alignment of the plate hole 110 with the test piece hole 20 until no alternating error signal is received from the photoelectric cell 3. Outputs 36, 37 corresponding to the X and Y components from the integrators 34, 35 can be presented visually in any suitable manner such as by digital volt meters (not shown) connecting one to each output 36, 37 and modified as necesary to give a suitable read-out.

The vibratory plate 11 is preferably supported in the housing 10 by spring means such as a blade spring assembly in which the spring mountings operate at right angles to one another in permitting the required circular motion of the plate 11. In accordance with the spring mountings the force coils 41, 42 are mounted from the plate 11 and each co-operate with a corresponding permanent magnet such as by a portion of the coil operating in a gap between the poles of the magnet. Thus the two coils 41, 42 operate at right angles to one another.

Thus, referring to Figures 3 and 4, the plate 11 having the hole 110 therein is mounted by pairs of blade springs 14, 1 5 from a base plate 17 having the clearance hole 100 in it or a central hole for the same purpose.

The lower pairs 14 of the blade springs upstand from the base plate 17 and are shown held by their feet 114 on the latter by a central clamping plate 117 through which the hole 100 also extends.

The blade springs of the pairs 14 have a resilient flexing action at 90C to that of the upper pairs 15 and the springs 14, 15 are shown connected to, or integral with, an intermediate ring 16. The upper springs 15 are shown similarly secured at 11 5 to the underside of the plate 11 by a central clamping plate 111 through which the hole 110 also extends.

Upstanding brackets 141, 142 from flanged edges of the plate 11 respectively carry the force coils 41,42 each having a portion operating in a pole gap 510, 520 of a corresponding permanent magnet 51, 52 mounted on the base plate 17.

As will be apparent the force coils 41, 42 and magnets 51. 52 are arranged at right angles to one another so as to respectively correspond to the pairs of blade springs 14. 15 for imparting desired vibratory circular motion to the plate 11 and hole 110 therein.

Flexible conductor connections (not shown) are made from the force coils 41, 42 to a terminal block 18 on the base plate 17 in order to allow for the vibratory movement of the coils.

The same arrangement is used for moving the plate 11 bodily where the latter and plate hole 110 are moved to alignment with the test piece hole 20 until no error signal is received from the photo-electric cell 3.

Claims

1. Apparatus for measuring or checking the position of at least one circular hole in a component or the like comprising at least one unit or head containing a source of parallel light and a plate having a circular hole therein for passage of said light and capable of circular vibratory motion in its plane about a relatively small circle and with constant orientation for corresponding circular motion of the hole axis, means within the unit or head for imparting said circular vibratory motion to the plate, the unit or head having an opening or window for passage of the light from the plate hole through a hole or corresponding hole in a component or the like when located with said hole in alignment (subject to any error) with the plate hole and between the latter and light responsive means of the apparatus, the apparatus further including means responsive to an error signal from the light responsive means in the event of variation in the light incident thereon due to said vibration of the plate and mis-alignment of the component or like hole with the plate hole.

2. Apparatus according to claim 1 wherein two or more of the units or heads are provided and are arranged for the measurement or checking of corresponding holes in a component or the like.

3. Apparatus according to claim 1 or 2 wherein the means within the or each unit or head for imparting circular vibratory motion to the vibratory plate therein consists of electromagnetic force coils operating at right angles to one another and acting on the plate.

4. Apparatus according to claim 3 wherein the coils of the electro-magnetic force coil means are connected to or carried by the vibratory plate.

5. Apparatus according to any of the preceding claims wherein the vibratory plate is supported within the unit or head by spring means.

6. Apparatus according to claim 5 wherein the vibratory plate is supported within the unit or head by blade spring means providing spring mountings operating at right angles to one another in permitting the required circular vibratory motion of the plate.

7. Apparatus according to any of the preceding claims wherein the means responsive to an error signal from the light responsive means and when so responsive, is arranged to operate the vibration imparting or force coil means to effect bodily movement of the vibratory plate to bring its hole into alignment with the hole in the component or the like in order to thereby obtain indication of the direction or extent of the positional error of said hole.

8. Apparatus for measuring or checking the position of at least one circular hole in a component or the like when substantially as herein described with reference to the accompanying drawings.