GB2064122A - Improvements in or relating to apparatus for measuring a dimension of an article - Google Patents

Abstract

An apparatus for measurement of the horizontal distance between two points on an article comprises a worktable (14) mounted on a frame (12) for rectilinear movement in a first (X) horizontal direction transversely of the frame (12). A microscope (16) is mounted on a support (32) of the frame (12) and is movable (32) in a second (Y) horizontal direction substantially at right angles to the first direction. Respective positional transducers are associated with the worktable (14) and the microscope (16) to provide electrical signals dependent on their positions relative to the frame. The signals are processed by respective digital displays (110, 112) which display in metric or imperial units the distances that the worktable and the microscope have moved from a preset datum in aligning the points on the article successively with the microscope graticule. A cross member 232 on the microscope carries lamps 234a, 234b. <IMAGE>

Description

SPECIFICATION Improvements in or relating to apparatus for measuring a dimension of an article The present invention relates to apparatus for measuring a dimension of an article.

Optical projectors and toolmakers microscopes have, for many years, been used for measuring small dimensions of articles, for example for checking the profile and surface finish of an article.

However, reasonable accuracy has only been possible where the dimensions being measured were extremely small and the article surface on which the measurement was being effected was generally flat and reflective. It has hitherto proved extremely difficult to obtain accurate measurements of large distances on irregular or low reflective surfaces such as are found in plastics and rubber articles and moulds and dyes.

It is quite often necessary, for example, to make accurate measurements of internal and external intersections of tapers, to determine hole centres on angular dimensions and to measure distances within a mould all of which prove extremely difficult to accomplish using conventional measuring techniques.

The present invention seeks to provide an improved form of apparatus for measuring a dimension of an article.

The present invention provides an apparatus for measuring a dimension of an article, the apparatus comprising a frame; a worktable mounted on said frame for supporting said article; optical means mounted on said frame for viewing said article, said optical means having alignment means for alignment with a preselectable location on said article; displacement means for enabling relative displacement of said article and said optical means in first and second substantially horizontal directions substantially at right angles to one another; positional sensing means for monitoring the relative movement of said article in each of said directions; and means for indicating said movement as a measured distance from a preselected datum.

In a preferred embodiment of the present invention the worktable is movable transversely of the frame in said first direction and the optical means which conveniently is in the form of a microscope is mounted on an upstanding support which is a part of the frame, the microscope being movable in said second direction relative to the upstanding support. The microscope is mounted such that it overlies the worktable. Both the worktable and the microscope are preferably mounted on respective carriages which are slidable relative to the respective portions of the frame by way of suitable linear bearings.

Movement of the carriages is effected by suitable gearing such as rack and pinion mechanisms, the racks preferably being secured to the frame while the pinions are secured on respective drive axles mounted in the associated carriages for rotation by an operator of the apparatus thus to move the worktable and the microscope in their respective directions.

Preferably the gearing for each carriage has both a coarse and a fine movement control, the coarse movement being effected by a simple 1:1 gear ratio while the fine movement is effected through a reduction gear of preferably 3 :1 ratio.

The positional sensing means preferably comprises a respective positional transducer, for example a mechanical-electrical transducer in the form of a potentiometer or an induction sensor, which is coupled to the associated carriage and which provides an electrical signal dependent on the position of the carriage. The indicating means advantageously comprises a respective electronic digital display associated with each positional transducer for converting the electrical signal into a digital display. Each digital display may be calibrated in metric or imperial units and conveniently can be set to zero at any preselected position of the associated carriage. The direction of movement of a carriage relative to a preselected datum is conveniently indicated on the digital display by means of a "+" or adjacent the measured distance displayed.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial front elevation, partly in section, of a preferred embodiment of an apparatus according to the present invention; Figure 2 is a side elevation, partly in section, of the apparatus of Figure 1 with the diascopic table omitted; Figure 3 is a part sectional view of the worktable and gear assembly taken on the line Ill-Ill of Figure 1; Figure 4 is a part sectional view of a modified form of gear for the worktable; and Figure 5 is a part sectional view of a further form of gear for the apparatus of Figure 1.

Figures 1 to 5 show an apparatus for accurately measuring distances between two points on a workpiece in both an X and Y axis direction of a substantially horizontal plane. The apparatus comprises a frame 12 on which is mounted a worktable 14 movable transversely across the frame 12 in a direction corresponding to the X axis of measurement along a line X-X, and an optical viewing system, here in the form of a travelling steroscopic microscope 1 6 having a graticule and, an objective lens and reflective mirror mounting 17, the microscope 1 6 being movable in a substantially horizontal plane in a direction corresponding to the Y axis at right angles to the X axis.The frame 12 comprises a housing 20 having front, rear and end walls 22, a sloping control panel 24 and a relatively thick top panel which constitutes a bed plate 26 of the apparatus.

A slide assembly 28 includes an upstanding pillar 30 slidably coupled to a stand 32 on which the microscope 1 6 is mounted. The stand 32 is vertically adjustable relative to the pillar 30 by a suitable rack and pinion gearing system to enable focusing of the microscope on a workpiece located on the worktable. Focusing is effected by an operator control knob 33.

The worktable 14 conveniently mounts a diascopic table assembly 13 (shown in Figure 1) and is carried on a gear assembly 1 5. The construction of the worktable 14 and its movement in the X direction is described below.

The worktable is generally shown with the diascopic table assembly omitted for clarity.

The end walls 22 of the apparatus are bolted to and upstand from the bed plate 26 and are rigidly interconnected by two bearing support bars 36. A bottom bearing support bar 38 is bolted to each support bar 36 and a respective linear half-bearing 39 is rigidly secured to each of the bars 36 and 38. The area extending between the end walls 22 is largely enclosed by concertina dust covers 13 to exclude dirt and dust.

The worktable 4 which is shown in partial section in Figure 3 comprises a circular head 42 having a flanged edge 44 with a slot 46. A knurled knot 48 extends through the slot 46 and is fixed to a ring 50 which is a snug fit within the flanged edge 44 and is rotatable with respect thereto by means of the knob 48.

The flanged edge 44 has a lip 52 upon which, in use, rests a thick metal plate 54.

Three centring arms 56 are pivotally attached to the ring 50 within the head 42 by means of pivots positioned equidistantly around the circumference of the ring 50. An underportion of a free end 58 of each arm 56 rests on the top surface of the head 42 and an upper surface of each arm is provided with a bush. Each bush is slidably engaged in one of three uniformly spaced slots provided in the plate 54 and curving outwardly from the plate centre. Each bush mounts a removable centring finger. Rotation of the knob 48 rotates the ring 50 thus causing the free ends of the arms 56 and thus the fingers to move along the slots. This enables substantially circular workpieces of varying diameters to be gripped on the table by the fingers.

A base portion 62 of the head 42 is provided with degree markings 63 on an external surface thereof and the head 42 is releasably held in engagement with the base portion 62 by means of a spigot 64 locatable in an aperture 65 upon which bears a screw-threaded rod 66 provided on the portion 62. The spigot 64 allows the head 43 to be rotatably positioned relative to the portion 62 and secured in that position by means of the rod 66. Alternatively the rod 66 may carry a toothed gear which meshes with teeth on the spigot 64 to allow rotation of the latter by turning a knurled knob 67 on the rod 66. Degree markings may alternatively or additionally be provided on the head periphery.

The base portion 62 is bolted to a carriage body 68, and a cavity 69 of U-shaped cross section is formed therebetween. A longitudinal member, 70, U-shaped in cross section, extends through the cavity 59 and is attached at each end to the end walls 22.

A rod 71 of circular cross section extends through an aperture provided in a part of the base portion bordering the cavity 69, and is lockable therein by means of a screw 72 threadedly engaged in portion 62. An end face of the rod 71 is aligned with and may, in use, abut an end face of a vernier screw gauge 74 mounted on one end wall 22.

Limbs 76 extend from the carriage body 68 and a linear half-bearing 78 is bolted to each limb, each half-bearing being co-operable with the associated half-bearing 39. The two bearings provided by the two parts of half-bearings 39, 78 support the carriage for movement transversely of the apparatus along the line X-X within the frame.

An axially extending U-shaped rebate 79 is provided on an underside of the carriage body 68 and a block 80 is bolted to a limb 82 forming one side wall of the rebate 79.

The gear assembly 1 4c includes a pair of axles 84a, 84b which extend through the block 80 and are supported thereby with the inner ends of the axles extending into the rebate 79 and the opposite ends of the axles 84a, 84b being provided with respective operating knobs 77.

The inner ends of the axles 84a, 84b carry pinions 128 (only one of which is shown in the drawings) one of which co-operates with a rack 86 bolted to the bed plate 26 to provide a 1:1 gear ratio whereas the other pinion is geared to the rack 86 via a reducing gear 134 which provides a 3:1 gearing ratio. The reducing gear 134 conveniently comprises a pinion which engages the rack 86 and is rigidly mounted on a spindle together with a larger diameter gear 142 which engages the spindle on axle 84b.

A modified form of gearing for the gear assembly is shown partly in section in Figure 4.

This comprises a housing 144 secured to the carriage body 58 and rotatably mounting a spindle 146 which carries a pinion 148. The spindle 146 is geared to a further spindle 1 50 by suitable gearing 152, the spindle 150 carrying a knob 77 (not shown in Figure 4).

A connector 90 is bolted to a limb 76a of the carriage body 68 by way of a spacer 88 and is operably linked to a positional transducer which monitors the position of the work table 14 along the X-X axis and provides an electrical signal in dependence on the position. The transducer is, for example, in the form of a potentiometer 92 bolted to the bed plate 26 by means of an aligning bracket 94. The positional transducer is electrically coupled to a digital display 110 of known type which can be reset at zero at any position of the worktable 14 on the X-X line to set a datum. The magnitude of travel of the worktable 14 from the datum is then displayed by the display 110 in preselected units, for example in metric or imperial units.

The control panel 24 mounts a switch for the mains electricity supply to the apparatus and switches to control lamps secured relative to the microscope 1 6 for illuminating the worktable and workpiece. Dimmer switches are provided for controlling the light intensity from the lamps.

The microscope 1 6 is rigidly supported on a carriage 200 which is in turn slidably mounted on the stand 32 so as to be movable in the Y direction. The carriage body 202 may conveniently be constructed in a similar manner to the carriage body 68 with lateral linear halfbearings 204 engaging in corresponding halfbearings 206 secured to the stand 32. The gear assembly for the microscope carriage 200 is conveniently constructed in a similar manner to the gear assembly for driving the worktable 14.

However, an alternative, simpler, form of gear assembly is shown in Figure 5 and is described below.

Figure 5 is a front elevation, partly in section through one form of gear assembly for the microscope carriage 200. The microscope carriage body 202 carries on its underside a rack 210 which cooperates with the gear assembly 212 mounted on the stand 32. The gear assembly comprises a spindle 214 on one end of which is rigidly mounted a pinion 216 which meshes with the rack 210. The spindle is rotatably mounted in bushes 21 8 which are in turn secured in a housing 220 secured in a through-bore 219 formed in one side arm 221 of the stand 32. The side arm 221 is the right side arm as seen in Figure 1 for use by a right-handed operator although the gear assembly may also be mounted in the left side arm if desired.The free end of the spindle 214 mounts a knob 222 to enable rotation of the pinion 216 by an operator, thus effecting movement of the carriage body 202 and the microscope 16 in the Y direction. The pinion 21 6 is conveniently geared to the rack 210 to provide a gear ratio of 3:1.

The carriage body 202 has a positional transducer 203 associated therewith in a similar manner to the carriage body of the worktable 14, the positional transducer being electrically coupled to a second digital display 112, similar to the digital display 110, to enable displacement of the microscope in the Y direction from a preselected datum to be displayed.

The objective lens and reflective mirror mounting 1 7 of the microscope 1 6 also carries a cross member 232 on which housings 234a and 234b for the lamps are mounted.

In use, to determine the distance between two locations in the X or Y direction on a workpiece the workpiece is placed on the worktable and the first location on the workpiece is aligned with a selected point on the microscope graticule. Both digital electronic displays are then zeroed to set a datum and the relative positions of the selected graticule point and the second location on the workpiece are adjusted by the operator using the control knobs 77 and 222 to move the worktable along the line X-X and the microscope in the Y direction. Once the selected point on the graticule is aligned with the second location on the workpiece the movement in the X and Y directions is read from the two digital displays.The straight line distance between the two locations can then be calculated mathematically since the two figures read from the digital displays form the dimensions of two sides of a right-angled triangle with the straight line distance forming the third side. Alternatively the distance can be calculated electronically for instantaneous display.

As an alternative to the above method prior to the measurement being effected the worktable can be rotated to align the two points in either the X or Y direction using the graticule as a reference so that only one movement is required with the distance being read directly off the relevant display.

A circular workpiece can be secured by moving the centring fingers 60a as far from the centre of the head as possible. This is achieved by rotating the knot 48 to the limit of its travel in one direction. The circular workpiece is placed approximately in the centre of the area bounded by the fingers and the fingers are then moved towards the centre of the head so automatically centring the workpiece.

Should the electricity supply fail and power not be available for the digital displays the vernier 74 can be used by the utilisation of slip blocks between the vernier and the rod 71 in known manner. The U-shaped member 70 acts as a tray to prevent slip blocks falling into awkward positions within the apparatus.

A print-out of the read-out given on the digital electronic display may conveniently be provided in the apparatus.

The apparatus according to the present invention provides a simple and accurate way of measuring dimensions of an article with large measurable ranges on both the X and Y axes. For example, in the illustrated embodiment the X axis measurable range is conveniently 1 2 inches (300 mm), while measurement on the Y axis is conveniently 6 inches (150 mm). Measurement can be effected to a resolution of 0.0001 inch (0.02 mm). The digital displays conveniently identify the direction of movement from a set datum by displaying a "+" or "" sign accordingly.

Claims (21)

1. Apparatus for measuring a dimension of an article comprises a frame; a worktable mounted on said frame for supporting said article; optical means mounted on said frame for viewing said article, said optical means having alignment means for alignment with a preselectable location on said article; displacement means for enabling relative displacement of said article and said optical means in first and second substantially horizontal directions substantially at right angles to one another; positional sensing means for monitoring the relative movement of said article in each of said directions; and means for indicating said movement as a measured distance from a preselected datum.

2. Apparatus as claimed in claim 1 wherein said worktable is mounted on said frame for movement in said first direction relative to said frame and said displacement means comprises a gear assembly coupling said worktable to said frame.

3. Apparatus as claimed in claim 2 wherein said gear assembly comprises a carriage on which the worktable is secured and which is slidingly coupled to the frame by way of linear bearings, and a rack and pinion mechanism for moving said carriage in said first direction.

4. Apparatus as claimed in claim 3 wherein said rack and pinion mechanism comprises a rack secured to one of said carriages and said frame and extending in said first direction and a drive axle rotatably mounted on the other of said carriage and said frame for rotation by an operator and engaged with the rack by way of a pinion.

5. Apparatus as claimed in claim 4 wherein two said drive axles are provided, one of which is coupled to said rack by a one to one gear ratio for coarse movement of said optical means and the other of which is coupled to said rack by way of a reduction gear for fine movement of said optical means.

6. Apparatus as claimed in claims 4 or 5 wherein said rack is secured to said frame and said drive axle is rotationally mounted on said carriage.

7. Apparatus as claimed in any of claims 2 to 6 further comprising a rod extending in said first direction and slidably engaged with said worktabie, one end of the rod being co-operable with mechanical measuring means; and locking means for securing said worktable to said rod.

8. Apparatus as claimed in claim 7 wherein said measuring means is a vernier screw gauge mounted on said frame.

9. Apparatus as claimed in any of claims 2 to 8 wherein said positional sensing means includes a first positional transducer coupled to said worktable for providing an electrical signal dependent on the position of said worktable relative to said frame.

10. Apparatus as claimed in claim 9 wherein said indicating means includes an electronic digital display coupled to said first positional transducer for displaying movement of said worktable in said first direction as a measurement of distance from said preselected datum.

11. Apparatus as claimed in any of claims 2 to 10 wherein said optical means is mounted above said worktable on an upstanding support of said frame for movement in said second direction relative to said frame and said displacement means includes a gear assembly coupling said optical means to said upstanding support.

12. Apparatus as claimed in claim 11 wherein said gear assembly comprises a carriage to which said optical means is secured and which is slidingly coupled to said upstanding support by way of linear bearings, and a rack and pinion mechanism for moving said carriage in said second direction.

13. Apparatus as claimed in claim 12 wherein said rack and pinion comprises a rack secured to one of said carriage and said upstanding support and extending in said second direction and a drive axle rotatably mounted on the other of said carriage and said upstanding support for rotation by an operator and engaged with the rack by way ofapinion.

14. Apparatus as claimed in claim 1 3 wherein two said drive axles are provided, one of which is coupled to the rack by a one-to-one gear ratio for coarse movement of said optical means and the other of which is coupled to the rack by way of a reduction gear for fine movement of said optical means.

1 5. Apparatus as claimed in claims 1 3 or 14 wherein said rack is secured to said upstanding support and said drive axle is rotatably mounted on said carriage.

1 6. Apparatus as claimed in any of claims 11 to 1 5 wherein said positional sensing means includes a second positional transducer coupled to said optical means for providing an electrical signal dependent on the position of said optical means relative to said upstanding support.

17. Apparatus as claimed in claim 1 6 wherein said indicating means includes an electrical digital display coupled to said second positional transducer for displaying movement of said optical means in said second direction as a measurement of distance from said preselected datum.

18. Apparatus as claimed in any of claims 1 to 17 wherein said optical means is a microscope.

1 9. Apparatus as claimed in any of claims 1 to 1 8 wherein said alignment means comprises a graticu le.

20. Apparatus for measuring a dimension of an article substantially as hereinbefore described with reference to Figures 1,2 and 3 of the accompanying drawings.

21. Apparatus for measuring a dimension of an article substantially as hereinbefore described with reference to Figures 1,2 and 3 when modified according to one of Figures 4 or 5 of the accompanying drawings.