Rexroth Tightening System 350 System Documentation - Rhino ...

10 Working with the System Tightening Technology | Bosch Rexroth AG 289/31610.4 Results storage and statistics10.4 Results storage and statistics10.4.1 Introduction10.4.2 Statistical terms and basicsIn order to be able to make a statement about the process within a tightening assembly, it is possible inthe BS350 operating system to statistically evaluate results.In practice it looks like this: The user demands that a certain set value (e.g. for torque or angle) be reachedin their concrete tightening case and expects that this value will be „reached exactly“ using the tighteningsystem. However, a certain deviation from the set value will always occur. To analyze these deviations, allresults are saved in a so-called results storage, which represents the basis for a statistical evaluation.In the BS350 operating system, the Results storage and statistics function is implemented for this statisticalevaluation. From the freely configurable results storage of the tightening controller, tightening resultsare read out and presented in a clear manner on different index cards (see page 299), as well asevaluated with the statistical methods necessary for the evaluation of a tightening.With the Results storage and statistics function the following statements can be made:– Estimation of the quality for tightenings currently running based on the statistical evaluation of randomsamples– Quality assurance and management– Proof of the reproducibility of tightening processes, repetition accuracy– Avoiding errors in the tightening process by recognizing deviations early and correcting them– Machine and process capability examinations (with the help of a reference system)– Comparison of tightening tools on the basis of concrete tightening cases to judge the quality (performance)of the nutrunner or tightening program– Trend recognition (what percentage of the tightenings will probably be within the tolerance limits demanded?)Statistical terms used in this document as well as in the BS350 under the menu item Results storageand statistics will be explained briefly below.StatisticsRandom sampleCharacteristicHistogramStatistics deal with the methods of gathering, sorting, summarizing, displaying and analyzing data, as wellas drawing valid conclusions.A random sample contains a random selection of data. They must be representative for all of the data (intightening technology this means for the entire tightening case).A characteristic is an attribute for certain objects. In tightening technology this means, for example:– Object = tightening or measurement data– Characteristic = torque, angle, etc.In order to display a large number of data clearly (here: read out from the results storage of the tighteningcontroller) statistics use histograms.A histogram separates all measurement data of the random sample into specific subsections(Fig. 10–54), since for the purpose of clarity, it is often not desirable or even possible to show each measurementvalue separately. These subsections (= columns) are called classes (m), which are characterizedby their width, limits and number. All measurement data is arranged in these classes. On the Y-axiseither the absolute or the relative frequency is given with which the measurement data occurred withinthe random sample.System 350 | 3 608 878 040/05.2008