GB2136997A

GB2136997A - Processing Sample Data

Info

Publication number: GB2136997A
Application number: GB08407338A
Authority: GB
Inventors: Renzo Franchi; Giambattista Cassani; Nello Griffanti; Luigi Felisari
Original assignee: Rockwell-Rimoldi SpA
Current assignee: Rockwell-Rimoldi SpA
Priority date: 1983-03-22
Filing date: 1984-03-21
Publication date: 1984-09-26
Also published as: DE3410572A1; GB8407338D0; JPS59230113A; IT8320207A1; IT8320207A0; IT1160818B; FR2543328A1

Abstract

An apparatus for processing data relating to measured physical properties of sample pieces as the data become available from a measuring apparatus comprises a transducer 4 which receives an analog quantity from a probe 3 and forwards it to an analog-digital converter 5 whose output is fed to a microprocessor 6 that has been previously programmed with limit values against which the digitized quantities from the converter are to be compared. The apparatus also includes visual and graphic display means 8, 18 whereby the relationship between the measured sample values and the limit values can be observed. The display may be a chart showing the mean value and range of the measurement data. <IMAGE>

Description

SPECIFICATION Apparatus For Processing Data As They Become Determined, and With Automatic Formation of the Control Chart In Terms of Mean X and Range W Background of the Invention Field of the Invention This invention relates to an apparatus for processing data as they become measured on samples withdrawn from produced batches. Each controlled parameter is determined by a measuring device connected to the apparatus and automatically forms a control chart by printing or a visual display in terms of mean X and range W, as subsequently explained more fully. The known art comprises measuring instruments for total or 100% control of the controlled parameters of all produced pieces, said parameters being either displayed one by one on a video screen or printed in sequence on paper.

The underlying concept of instruments using this type of measurement is to make the appropriate corrections to the machine, and thus to the production process, when the controlled parameters assume values which approach the tolerated error limits.

In this respect, controlled parameters may include surface characteristics, dimensions, and all other characteristics which determine the quality of the piece.

However, an inherent drawback of these existing instruments is that the error has to be corrected after it has been determined, and thus after the piece has been recognized as a reject.

Moreover, the existing procedure for compiling a control chart is manual, and is therefore inevitably subject to errors such as to compromise its validity.

This existing procedure has therefore been superseded by statistical control of the production process by compiling a control chart which carries two diagrams: On the first diagram, showing the mean values X, the central line X is traced, and at equal distances above and below this central line the upper limit line LSX and the lower limit line LIX are traced as a function of the tolerance of the piece under control. Points equal to the mean of the measured values of each sample are shown on this diagram.

On the second diagram, which shows the range W, the central lineW is traced, and above and below this central line the upper limit line LSW and lower limit line 0 are traced as a function of the tolerance of the piece under control.

This diagram shows the points equivalent to the difference between the maximum value and minimum value of each measured sample.

The following example is reported to illustrate better how a control chart is compiled. A piece with diameter of 10 mm and tolerance h 5 is equivalent to the interval from 0 to -0,006 as reported in tables from the International Standards Organization.

For the statistical control applied to the production, it is well known in this case that tolerance 6 a= - = =1 micron.

6 6 The central line X corresponds to tolerance 6 =~ =-3.

2 2 The upper limit line LSX corresponds to X+Aa=-3+1,5x1=-1,5 (A=1,5 for each sample of 4 pieces).

The lower limit line LIX corresponds to X+Au=-3-1 ,5x 1-4,5.

Therefore, it is possible now to trace the parallel lines X, LSX and LIX as reported in Figure 1, relating the mean values X diagram.

The measured values of each of the 13 samples composed of four pieces, are reported successively on the line referred to the numbers 1 to 13.

At right side of each of the lines, the mean of the values are reported on the column X and on the diagram mean values X.

It is well known that the central line W corresponds to d2ci=2,059x 1=2,059 (d2=2,059 for each sample of 4 pieces).

The upper limit line LSW corresponds to Da=4,698x 1=4,698 (D=4,698 for each sample of 4 pieces.) The lower limit line corresponds to 0.

Therefore, it is possible now to trace the parallel linesW, and LSW, as reported in Figure 1 relating the range values W diagram.

At right side in respect to the mean values X, the values as differences between the maximum and the minimum values of each measured sample are reported on the column W and on the range values W diagram.

In this manner, the progress of the mean values for each withdrawn sample and consequently the state of production of the pieces under control can be seen, said limits covering a zone of tolerable errors within the natural tolerance of the machine tool which produces the piece.

In this respect, every machine tool is known to have its own machining accuracy, its natural tolerance indicating after how many produced pieces a check must be made on sample pieces withdrawn from the batch. This determines the so-called sampling frequency and the extent of the sample, i.e., the number of pieces which constitute the sample to be taken from the batch of produced pieces. For instance, in the abovedescribed example, the frequency is 40, the sample is composed of 4 pieces and the batch is composed of 520 pieces, so that 13 samples are withdrawn at a frequency of one for each 40 pieces produced.

By utilizing the natural tolerance of the machine tool in this manner, statistical control can be used in a production process instead of 100% control of the produced pieces.

In contrast to 100% control, statistical control of the production process by interpreting the control chart offers the indubitable advantage of correcting the error and thus the production process before the produced piece becomes a reject piece. In other words, the pieces produced between two successive samplings will consist of "good" pieces, or, at worst, pieces "to be subjected to selection." However, the compilation of the control chart requires accuracy, order, system and the ability to mentally calculate statistical means, with the result that as this is a manual calculation the operation is disadvantageously long, and the document is of little reliability.The present apparatus offers the important advantage that the control chart is automatically printed or displayed, directly and immediately, at the instant in which the measuring device checks the produced pieces which constitute the withdrawn sample.

This apparatus, besides displaying the determined and processed values on a video screen, prints the values in the form of typographical signs and numerals which represent the means of the determined values.

Moreover, the measuring device, such as an device for determining dimensions, surface finish, planarity, etc., can be connected to the processing apparatus according to the invention for adaptation to any machine tool, independently of the type of production process in which it is used.

Summary of the Invention The object of the present invention is therefore to automatically obtain a control chart in printed and/or visually displayed form in terms of mean and range W as a means for proving the conformity of the controlled parameters, i.e., to give immediate indication regarding the control state of the parameter under examination.

The technical problem of the present invention is to provide an apparatus of small size capable of processing data determined during the control operations, by converting these values into data or graphical symbols sequentially printed on paper or visually displayed one after the other, in zones which are divided into classes of values corresponding to the determined values.

The solution to this technical problem is obtained by an apparatus for processing the data of each sample as they become determined by a measuring device connected to the apparatus for each controlled parameter, and with the automatic formation of the control chart by printing and/or visual display, with the characteristic that the probe of the measuring apparatus is connected to a transducer for the individual measured data items of each sample, which is connected in its turn to an analog-digital converter which by way of a microprocessor, to which the limits of X and W are fed as input, executes the graphs of the control chart by printing and/or visual display.

Brief Description of the Drawings Further characteristics of the present invention will be apparent from the description of the present invention given hereinafter by way of non-limiting example, and illustrated by the accompanying drawings in which: Figure 1 is an example of the control chart manually compiled; Figure 2 is a view of the apparatus according to the invention connected to the measuring device; Figure 3 is a block diagram of the apparatus; and Figure 4 is an example of the control chart as printed by the apparatus.

The apparatus 1 for processing the data of each sample as they become determined by the measuring apparatus 2, which is provided with the probe 3 for measuring the controlled parameter, is connected to said apparatus by the cable 3' which passes through the inlet E of the apparatus 1. Said probe 3 is connected inside the apparatus to the transducer 4 for the individual measured data items of each sample of pieces, and which is connected in its turn to the analog digital converter 5, which by way of the microprocessor 6, to which the lower limit LIX and upper limit LSX and the upper range limit LSW are fed as input by means of the "numerical counter" 7 or a suitable keyboard, effects the printing of the graphs of the control chart 8. This latter can be obtained with visual display of the graphs instead of printing.The reference numerals 9, 10, 1 1, 12, respectively, indicate the lamps which light when appropriate to indicate readiness to receive the input of said limits LIX, LSX and LSW, and when an error is inadvertently committed.

The letter I indicates the apparatus switch, and the reference numerals 13, 14, 15 and 16 indicate lamps which light when appropriate to indicate readiness to receive the measurements of the 1 st, 2nd, 3rd and 4th piece of each sample.

The analog-digital converter 5 is also connected to the dimension indicator 17, which displays the individual component data items of each sample as they are measured.

The microprocessor 6 is also connected to a visual indicating device 18, to provide an indication of the state of the data with respect to the fed limits of X and W. This visual indicating device comprises three signals 19, 20, 21 in the form of green, yellow and red light, respectively.

The first light indicates that the measured data and thus the production corresponding to the withdrawn sample are within the set limits, the second light indicates that at least seven data items deviate in the same direction from the mean; and the third light indicates when any data item goes outside one of the limits. We suppose that the piece under control is the same as above considered in relation to the manually compiled control chart reported in Figure 1.

Therefore, in the case of the control chart 8 automatically produced by the apparatus, the chart emerges from the instrument continually in steps, printed in the form of rows, as shown in Figure 4, on which the li les LIX, X, LSX, O, W and LSW are printed with the points (small rectangles) and corresponding numerical values.

These values are the same as reported on the column X and W of Figure 1. These points can be joined together ideally in the form of a graph, the points which are outside the limits LIX, LSX or LSW being printed on the limiting lines and indicated with a special sign shown by reference P in Figure 4 in addition to their numerical value.

If the control chart is displayed on a screen, the data are shown, for example, in green if with the limits, and in red if outside the limits, or by other suitable differentiating signs to indicate these two events.

In the case of visual display, an optional printer of the final result is provided interfaced with the microprocessor 6.

A further inlet E' can be provided coupled to the inlet E, for making measurements with a further summation or difference probe.

When several parameters are simultaneously controlled, further inlets are provided for connection to the various probes of the further measuring devices. In the case of several controlled parameters, a number of control charts equal to the number of said parameters is therefore provided, or alternatively, a single chart containing a number of graphs equal to the number of controlled parameters. Other modifications can be made to the present apparatus, without leaving the scope of the present invention.

For the use of said instrument, firstly, the switch I is put on position, "on," and connected to the measuring device 2 with the inlet E of the apparatus 1 by the cable 3'. Then, the limits LIX, LSX and LSW, previously calculated in conformity with the rules of the manual compiling of the control chart as above reported, are fed into the apparatus, as evidenced on the numerical counter 7, by means of the push button T, in the sequence shown by lighting of the lamps 9, 10, 1 1.

If no error is committed, the lamp 12 does not light and on the control chart 8 the first part of the limits LIX, X, LSX, O, W LSW are printed, as shown by the reference F in Figure 4 and microprocessor is ready to receive the four measurements of the first sample.

Therefore the four pieces comprising said first sample are measured by the device 2 and the lamps 13, 14, 1 5, 16 light to indicate readiness to receive said measurements.

When the microcomputer 6 receives the 4th measurement, it elaborates the data and produces the printed part shown by the reference F' in Figure 4 referred to the first 4 pieces.

After the operation of measurement of the pieces of the subsequent samples, the corresponding printed part of the control chart 8 emerges step by step from the instrument.

Further by watching the control chart, the apparatus 1 allows a good evaluation of the production process, also the lighting of one of the three signals 19, 20, 21, respectively, of different colors shows the condition; green showing that the process is in order, yellow showing that the process is tending to produce pieces out of control, and red showing that the process is out of control.

In this case, it is necessary to effect correction and control of the pieces produced in the last two samples.

On the line LIX of the control chart 8 a small rectangle P appears of different aspects in comparison to the other points, with the corresponding numerical value.

Claims

1. An apparatus for processing product sampling data received from sensing devices for comparison with pre-stored value limit data and producing visual output indicative of the physical condition of the sampled product, said apparatus comprising: (a) a transducer to receive a signal indicative of a physical parameter of a sample measured by a suitable measuring device; (b) a converter connected to and receiving an analog output from said transducer to convert the analog input to a digital output representative of the measured parameters; (c) a microprocessor having pre-stored value limit data therein connected to said digital converter to receive the output therefrom and compare it to the pre-stored value data; and means connected to said microprocessor to produce a reviewable display showing the results of the comparison between the pre-stored and the sampled data.

2. An apparatus as defined in claim 1, wherein said apparatus also comprises means connected to receive the output of said analog to digital converter to display the dimensions of each product as it is sampled.

3. An apparatus as defined in claim 1, wherein said microprocessor is connected to a visual indicating device for the compared results.

4. An apparatus as defined in claim 1, 2 or 3 wherein pre-stored value limits are fed to said microprocessor by means of discrete pulse input means.

5. An apparatus as defined in any preceding claim wherein said reviewable display is a control chart which emerges stepwise from the instrument and presents the comparative data as printed rows on which points are printed together with their numerical mean values X and range values W, the points which are outside the limits being indicated by a special sign in addition to their numerical value.

6. An apparatus as defined in any preceding claim wherein a CRT is provided to display the comparative data on a screen, and wherein the comparative data within the limits and outside the limits are shown respectively by differentiating signs.

7. An apparatus as defined in claim 3 or in any claim dependent thereon, wherein the visual indicating device for the comparative data is constituted by three signals in the form of green, yellow and red lights, the first light to indicate that the measured data and thus the production corresponding to the sampled product are within the set limits, the second light to indicate that at least seven data items deviate in the same direction from the mean, and the third light indicates as soon as any data item goes outside one of the limits.