GB1585215A - Inspection templates - Google Patents

Description

(54) INSPECTION TEMPLATES (71) W, The FURNITURE INDUS TRY RESEARCH ASSOCIATION, a British Company, of Maxwell Road, Stevenage, Herts, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: The invention relates to inspection templates for use in wood working and other industries.

In such industries, especially the furniture industry, it is necessary to transfer to a workpiece, such as a panel, various patterns of the location of holes or slots or grooves in the course of manufacture of finished structures. For example, it is often necessary to provide a panel with the correct location of a series of.holes and/or slots such that the various holes and slots may be properly aligned with corresponding features on other panels for the purpose of building up a part or a completed piece of funiture.

Traditionally the appropriate locations have been checked with measuring instruments on a limited sample of a series of identical panels. This is slow and any mistake in the process can render many panels useless.

According to the invention there is provided a method of testing the location of surface features formed on a workpiece comprising (1) superposing the workpiece and an optical template comprising a sheet of transparent material having marked thereon the intended location of the surface features, the marking in respect of each suface feature being such as to embrace the intended location of that feature and such as to indicate a predetermined positional tolerance of that feature with respect to each of a pair of given datum axes, and (2) viewing the surface features through the template.

The markings on the template should be clear, well defined and resistant to abrasion.

It has been found that a cutter head driven typically by an electric motor can advantageously be used as a scriber to form the marking on the template. The scribings can be made more apparent by being filled with a coloured material, such as a wax.

In order to provide a further advantage-of enabling the template to be used for checking the accuracy of holes of lines on workpieces, it is desirable that the template be made of a transparent temperature and humidity stable material. Polyester films sold under the Trade Marks Mylar or Melinex have been found particularly suitable in meeting these requirements.

The use of a motor-driven cutter, for example with a diamond or sapphire point, positioned by an appropriately programmed computor, as the scriber for marking on the template, is particularly advantageous.

In addition to indicating the positional tolerances of the intended slots and holes, the scriber can also be used to indicate the preferred precise location of such holes and slots; the tolerances on panel widths and lengths may be among those indicated. This is particularly desirable so as to facilitate checking the accuracy of the holes and slots of the finished workpiece.

By means of the device of the invention it has been found possible to secure tolerances better than 0.2 millimeters per metre, which represents a considerably increase in the accuracy of the finished workpiece as compared with the conventional practice in the furniture industry.

The invention is particularly applicable to workpieces of the material generally found in the funiture industry, especially wood, and wood derivatives. In addition to the furniture industry, it is applicable for example, in such fields as the production of wooden toys, the engineering and packaging industries.

Preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates a dimensioned and toleranced drawing of a simple panel exhibiting two drilled holes, a slot and a cut out.

Figure 2 illustrates the associated optical template of the present invention.

Figure 3 is an enlarged detail view of one of the hole position checking markings on the template shown in Figure 2.

Figure 4 is an enlarged detail view of a cut-out edge position checking marking.

Figure 5 is an enlarged detail view of a workpiece edge position checking marking.

Figure 6 is an enlarged detail view of slot position checking markings.

Figure 7 is an exploded view of one of the datum position buttons to be connected to the template shown in Figure 2.

In Figure 1, a panel 10 is shown formed with two holes 11 and 12, a groove 13 and a cut-out corner portion 14. The position of each of these features on the panel 10 is decided upon, together with the permitted tolerance by which each feature is allowed to deviate from its true co-ordinate position.

As indicated these co-ordinates are determined with respect to two adjacent edges 15 and 16 of the panel 10 at right angles to one another.

As indicated in Figure 2, the correct position of each of the feaures is indicated as surface markings on a transparent template 17, together with an indication of the permitted tolerances.

Each feature of the template 17 will now be described in detail.

In Figure 1 it can be seen that the axis of the Q)Smm hole 12 is allowed to deviate from its true co-ordinate position of x = 150mm and y = 100mm by an amount up to + 0.3mm along both axes. In providing a method of visually checking that a hole, produced in a panel by any appropriate means, is within the prescribed tolerance, four lines are drawn or scribed on the transparent template 17 to form a square 18 such that the inner edges of these lines presents a boundary within which the complete hole must be contained, when the template is accurately positioned over the panel. Being an inspection aid, the lines must be clean and accurately positioned in relation to other features in addition to two or more datum points.Although it is possible that the lines could be put down by manual means is is more economical to employ a computer controlled line plotter.

As measurements are made against the inside edge of the lines. it follows that their thickness is immaterial. although lines of known thickness. typically 0.2mm, can be of assistance in estimating hole positional error when the edge of the hole is touching or is outside the outer edge of the line.

As a further example of hole position inspection, the centre line of the 1D lOmm hole 11 is permitted to deviate along the x axis by up to + 0.4mm while along the Y axis it must be controlled within 1 0.2mm.

Accordingly, the envelope displaying the permitted deviation becomes a rectangle 19.

Figure 3 illustrates the envelope 18 for the Q)Smm hole 12.

For checking positions of the cut-out 14, a pair of full or broken lines 20 are provided for each edge 21 of the cut-out with the inner or opposing edges of the paired lines forming the maximum and minimum position. Figure 4 illustrates the positioning of the lines.

As indicated in Figure 5, panel widths and lengths can also be assessed with the optical template as double broken lines 22 for each edge 23 of the panel. The other edges 15 and 16 are of course the datum edges against which the template 17 is initially aligned as described below.

For checking position of groove or slot 13, one of two methods can be used as illustrated by Figure 6. On the left hand side of this Figure a single pair of broken lines 24 are used within which the edges of the slot 13 must fall and on the right hand side a pair of lines 25 are used for each edge of the groove 13. The method employed will depend upon the method used to dimension the position of the groove.

Location of the template 17 with respect to the work piece 10 is by means of abutments on the template aligned with the datum axis, for example datum buttons 31 positioned at selected positions on the template. Such abutments may desirably be formed in two parts which are secured to each other from opposite sides of the sheet of transparent material. Although the abutments can be of any shape or size, circular units as shown by Figure 7 have been found to be particularly suitable both to manufacture and in fastening to the template. The illustration shows that such unit comprises of two main parts 27, 28 with one or more fastening screws (not shown). As shown, the part 27 consists of a large diameter head portion 29, typically of 25mm diameter and a smaller diameter shank 30, typically of lOmm diameter. The part 28 consists of an annular member of 25mm outer diameter and 10mm inner diameter. This annular member fitting over the shank 30 of the member 27. On both parts 27, 28 the 10mm and 25mm features are produced to close manufacturing tolerances and held truly concentric to each other. The tolerence on the 810mum spigot and hole are such that a precision location fit is ensured upon assembly. At selected positions on the template 17, a number of 10mum holes 31 are pierced with their centres precisely at 12.5mm from the datum lines. Clearance holes for the fastening screws are also provided.Either the centre of the datum lines, or the inner edge thereof, may for example be used as the true zero of "datum" from which the distance is measured.

It can now be seen that the purpose of the 810mum spigot is two fold in that it provides location between the two halves of the datum button and precise location for the assembled unit in respect to the scribed lines on the template.

To enable the position of the buttons 31 to be checked, optional check lines 32 may be scribed on the template 17 typically at 20mm precisely from the datum lines. After assembly of the buttons, any error, introduced when punching the 10mm holes, can be determined and the 25mm of the two portions 27, 28 adjusted, if necessary to correct any such error.

Although the provision of two buttons 31 along the long side and one along the short side will give kinematic restraint, it is sometimes desirable that more than two location buttons are required along the long side and more than one along the short side.

Where multiple datums are used, typically as a result of machine restraint, then provisions for the location buttons are made on all sides of the templates.

Although broken lines have been used in the above descriptive paragraphs, they can be replaced with full lines or a combination of full and broken. The length of the broken lines typically 10mm can also be varied to suit any application. The double tolerance line can be replaced with a single line.

The template 17 can be made of single or laminated sheets of polyester film i.e. Mylar or Melinex, in any thickness or any other suitable clear or tinted, substantially transparent stable material. However, the use of thin film has the advantage that it allows a single template to be used for both left and right handed components without problems created by parallax.

The template 17 can also be used as an aid in setting up the machine (not shown) to be used in producing the holes, etc., in the panel 10. Typically such a machine consists of a workpiece supporting frame mounted in relationship to a workbed on which are positioned mounting chucks or collets for drills, etc., which are raised upwardly from the bed to cut the workpiece at the appropriate point. The co-ordinate position of each of the chucks is adjusted by the use of the template 17 by positioning a miniature projector in each of the chucks and positioning the template 17 in the workpiece supporting frame. Each of the projectors projects an imge of a centering crosswire for example, onto the template 17 and the position of the chuck is then adjusted to accurately centre the crosswire on the position marking on the template.

WHAT WE CLAIM IS: 1. A method of testing the location of surface features formed on a workpiece com rising (1 superposing the workpiece and an optical template comprising a sheet of transparent material having marked thereon the intended location of the surface features, the marking in respect of each surface feature being such as to embrace the intended location of that feature and such as to indicate a predetermined positional tolerance of that feature with respect to each of a pair of given datum axes, and (2) viewing the surface features through the template.

2. A method as claimed in claim 1 wherein the marking on said template corresponding to a circular hole to be formed on said workpiece comprises a rectangle the sides of which are parallel to said datum axes, and wherein the lengths of the sides of the rectangle correspond to the diameter of the circle plus the permitted positional tolerance along the particular datum axis.

3. A method as claimed in claim 1 or claim 2 wherein the marking on said template corresponding to a feature on said workpiece comprises pairs of spaced parallel lines, the members of each pair being spaced apart by an amount corresponding to.

the permitted positional tolerance of the feature.

4. A method as claimed in claim 3 wherein the said lines on the template are in the form of discontinuous dashed lines.

5. A method as claimed in claims 3 and 4 wherein, when said feature on said workpiece is a groove or slot.

6. A method as claimed in any preceding claim wherein abutments are provided on said template aligned with the datum lines thereon such that when is use on a workpiece, the abutments are brought into contact with the edges of said workpiece which define the datum axes thereof.

7. A method as claimed in claim 6 wherein said abutments are formed in two parts which are secured to one another from opposite sides of the sheet of transparent material forming said template.

8. A method as claimed in claim 1 substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. upon assembly. At selected positions on the template 17, a number of 10mum holes 31 are pierced with their centres precisely at 12.5mm from the datum lines. Clearance holes for the fastening screws are also provided. Either the centre of the datum lines, or the inner edge thereof, may for example be used as the true zero of "datum" from which the distance is measured. It can now be seen that the purpose of the 810mum spigot is two fold in that it provides location between the two halves of the datum button and precise location for the assembled unit in respect to the scribed lines on the template. To enable the position of the buttons 31 to be checked, optional check lines 32 may be scribed on the template 17 typically at 20mm precisely from the datum lines. After assembly of the buttons, any error, introduced when punching the 10mm holes, can be determined and the 25mm of the two portions 27, 28 adjusted, if necessary to correct any such error. Although the provision of two buttons 31 along the long side and one along the short side will give kinematic restraint, it is sometimes desirable that more than two location buttons are required along the long side and more than one along the short side. Where multiple datums are used, typically as a result of machine restraint, then provisions for the location buttons are made on all sides of the templates. Although broken lines have been used in the above descriptive paragraphs, they can be replaced with full lines or a combination of full and broken. The length of the broken lines typically 10mm can also be varied to suit any application. The double tolerance line can be replaced with a single line. The template 17 can be made of single or laminated sheets of polyester film i.e. Mylar or Melinex, in any thickness or any other suitable clear or tinted, substantially transparent stable material. However, the use of thin film has the advantage that it allows a single template to be used for both left and right handed components without problems created by parallax. The template 17 can also be used as an aid in setting up the machine (not shown) to be used in producing the holes, etc., in the panel 10. Typically such a machine consists of a workpiece supporting frame mounted in relationship to a workbed on which are positioned mounting chucks or collets for drills, etc., which are raised upwardly from the bed to cut the workpiece at the appropriate point. The co-ordinate position of each of the chucks is adjusted by the use of the template 17 by positioning a miniature projector in each of the chucks and positioning the template 17 in the workpiece supporting frame. Each of the projectors projects an imge of a centering crosswire for example, onto the template 17 and the position of the chuck is then adjusted to accurately centre the crosswire on the position marking on the template. WHAT WE CLAIM IS:

1. A method of testing the location of surface features formed on a workpiece com rising (1 superposing the workpiece and an optical template comprising a sheet of transparent material having marked thereon the intended location of the surface features, the marking in respect of each surface feature being such as to embrace the intended location of that feature and such as to indicate a predetermined positional tolerance of that feature with respect to each of a pair of given datum axes, and (2) viewing the surface features through the template.

2. A method as claimed in claim 1 wherein the marking on said template corresponding to a circular hole to be formed on said workpiece comprises a rectangle the sides of which are parallel to said datum axes, and wherein the lengths of the sides of the rectangle correspond to the diameter of the circle plus the permitted positional tolerance along the particular datum axis.

3. A method as claimed in claim 1 or claim 2 wherein the marking on said template corresponding to a feature on said workpiece comprises pairs of spaced parallel lines, the members of each pair being spaced apart by an amount corresponding to.

the permitted positional tolerance of the feature.

4. A method as claimed in claim 3 wherein the said lines on the template are in the form of discontinuous dashed lines.

5. A method as claimed in claims 3 and 4 wherein, when said feature on said workpiece is a groove or slot.

6. A method as claimed in any preceding claim wherein abutments are provided on said template aligned with the datum lines thereon such that when is use on a workpiece, the abutments are brought into contact with the edges of said workpiece which define the datum axes thereof.

7. A method as claimed in claim 6 wherein said abutments are formed in two parts which are secured to one another from opposite sides of the sheet of transparent material forming said template.

8. A method as claimed in claim 1 substantially as hereinbefore described.