Introduction 

CiS.01 is an automatic crack detection system to monitor cracks and breaks in operations with workpieces under  mechanical load.

Mainly CiS.01 is suitable to detect cracks in  shafts during straightening in a straightening press.

Special features that are related to the straightening application are strongly considered when designing CiS.01 .

Every day thousands of steel shafts are scrapped throughout the automobile industry as  many shafts could not withstand the high mechanical load during bending/straightening.

At the same time there is the risk of building in defect shafts into gear boxes when a defect has not  been detected before.

Advantages

CiS.01 offers advantages in two fields:

1.        Strong signal gap in filtering defect workpieces.

2.        Providing information to optimise the straightening process and to reduce scrap.

In order to achieve this advantages CiS.01 is equipped with these new features::

·         Optimised signal detection ( sensor, amplifier, evaluation)

·         Precise adjustment of measuring to the definite workpiece.

·         Complex self test function to proof the availability of the system

·         All measured data are saved for statistic analysis

·         All data are provided for modern communication standards ( Intranet, e-mail etc.)

·         Easy handling through automatic setting and adjusting features .

Signal evaluation

The sensor converts the signal. It then gets amplified and filtered over frequency. So signal of low frequency, that often are caused by mechanical noise can be suppressed.

table 1 (Signal Amplitude)

Those signal components that are larger then the noise level adjusted (Noise Limit: typically 2,5 ‰ of field of interest) are subject to an energy evaluation.

A large amplitude leads to a quick rise of the signal energy. A little signal amplitude only provides a slow rise of energy.

table 2 (Signal Energy)

In case of crack the signal energy  the curve normally builds up as shown above .

The workpiece is evaluated as cracked when there is overflow in " Limit Crack ".

The workpiece is evaluated as broken when there is overflow "Limit Break" .

The limit for the suppression of  noise relates to the signal amplitude.

The limit for crack and break relate to the signal energy.

A crack can already be identified in the lower end of the energy measuring. The difference between crack and break energy can be set large enough to enable a clear distinguishing to the   significantly larger break signal.

Conditions for precise recognition:

1.        Good coupling of sensor to machine

2.        Signal transmission and amplification with little noise

3.        Parameter setting of monitor related to the actual workpiece

4.        No changes of measuring sensitivity of the whole measuring system

There is a number of different influences that may cause difficulties in detecting cracks. Ignoring these information can lead into wrong results of measuring

Sensorial Aspects

All piezo electric sensor systems show significant resonance in different frequencies..

The resonance picture depends on the structure of the sensor. Also the coupling  of the sensor to the machine and by the machine element itself influence the resonance.

A reliable  judgement about the sensitivity of the sensor can only be made  after the sensor is mounted to the actual machine.

Measuring sensitivity of the sensor under  laboratory conditions will not allow any prediction to the impulse answer  under production environment.

CiS.01 solves this problem by measuring the sensor right after mounting to the machine.

The impulse is thereby stated by the sensor itself.

If the impulse is stated by a second impulse actor no information on the coupling of the sensor or the  actor would be available.

CiS.01 is using a sensor to create an impulse as well. So the coupling for impulse and measuring is the same and can be metered.

The piezo element is fitted into a cylindrical shaped alloy steel housing.

This housing is bolted by a central bolt to the machine.

Thus the piezo element receives largest possible service contact to the machine.

There is no preferred direction for mounting to the machine. 

The contact surfaces must be as flat and fine as possible and may not have any coatings or dirt that could influence the signal transmission.

It is helpful to mount the sensor to the machine as close to the shaft as possible as the energy is higher the closer  the sensor is to the place of cracking.

Signal  noise

The measuring system is completely equipped with differential amplifiers and transmitters..

CiS.01 allows adjustment of the noise suppression to adjust to individual production environments

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Adjustment related to the actual workpiece

The energy that is induced  by the workpiece when cracking depends strongly on the pressure load that had been put to the workpiece.

Small workpiece diameters show different  tensile strength than larger diameters. Geometric steps may also reduce the tensile strength of the workpiece.

CiS.01 offers to set up to 10 different configurations per workpiece.

These different configurations may be set by different  combinations of position of hammer and  shaft holders.

For every measuring position signal amplification, noise suppression, rejection level for crack and break may be set differently ( according to different shaft design such as geometry, cut ins .. )

The conditions of measurement could be different for different workpieces too.

Because of that, CiS.01 has a storage for 50 different workpieces, where the special parameters applying to the defined measuring positions can be stored.

So, after a set of parameters is defined, a special set for an individual workpiece can be selected manually by the operator or automatically by the straightening press.

Constant sensitivity of measurement

With every new workpiece (a special signal indicates the workpiece transport to the crack detection unit) a three step selftest is executed by the detection unit.

1.        By comparing the special capacities of cables and sensors the unit checks the electrical connection of cable and sensor to the preamplifier.

2.        By stimulating the measuring system with a very pricise sine wave, the characteristic curve of the electrical system is compared to the originally calibrated curve.

3.        The actual coupling between sensor and the machine element is checked by the so called impulse test. The actual measured value of the coupling is compared with the originally measured and stored value.

All these tests are executed simultaneously with every change of a workpiece and for up to 8 connected sensors.

If sensors were changed or modifications at the machine were made, the coupling of sensor and machine will change too.

CiS.01 will notify these changes in the coupling. This different coupling means that there is also a different transfer characteristic of the whole system. So CiS.01 indicates a fault.

After a simple modification of the machine without changing a sensor it is mostly possible to bring the coupling into the specified range.

If this is not possible, the new coupling value must be stored.

A changed coupling influences the measuring sensitivity.

The higher the coupling the higher the measuring sensitivity.

Data Security

All changes of parameters are protected by a 5 level password system.

So only authorized operators can change the system.

Measuring data for statistical evaluation

CiS.01 is equipped with a storage for measured values, that has the capability to store up to 400,000 workpieces.

For every workpiece CiS.01 stores a serial number, a reference to the type of workpiece, date and time of manufacturing, the number of strokes and the results of measuring. 

And additionally the measuring result of every stroke (no matter if cracked or not) is stored.

So by evaluating these data it is possible to recognise changes in the noise level of the machine, as a result of changes in the quality of the tools or the system at all.

So you can maintain the machine very early, before getting faults or damaged workpieces because of wear

Changes made in the preceding manufacturing often become obvious under straightening stress.

The evaluation of all measured data can help to decide about the advantages or disadvantages of changes in different steps of the production.

For small amounts of data it is suitable to use a line printer, that can be connected directly to the crack detection device.

 It is also possible to send the data to a serial terminal, if there is a computer connected at the serial RS232 connector of the CiS.01 unit.

To get more extensive statistical information it is recommended to use an ethernet connection and a file transfer with FTP protocol. 

After an FTP transfer the data is ready for evaluation or storing in an archive system.

Information about unit status

In addition to the transfer of statistical data, it is possible to have access to all the unit parameters.

Therefor CiS.01 is equipped with a built in WEB Server.

With any WEB Browser (it should have java capabilities) you can connect to the crack detection device and have a look on its settings.

CiS.01 can be connected to an Intranet system and configured in a WEB Browser. Access is protected by a password system.

Adjustments – easy/automatic

The adjustment of  the measuring sensitivity and the noise suppression for the test functions and the parameter setting for a single workpiece can be done in a teach procedure.

All settings of the unit can be changed by software. The same CiS.01 unit is suitable for different types of straightening presses or  different numbers of hammers.

The integration of a CiS into a definite machine is normally be done by changing  software parameters.