Montage Anleitung ENGLISCH.pmd

Transcription

ROLAND
ROLAND ELECTRONIC GmbH
Otto-Maurer-Str. 17 · D-75210 Keltern
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5.04.2002 / Page 1
Mounting instructions
for double sheet control
ROLAND
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This documentation has been carefully prepared. However errors or misinterpretations cannot be
completely excluded. Please contact us immediately if you detect any ambiguities or encounter problems
of understanding. We will do our best to assist you. We reserve the right to improve this documentation
anytime without prior announcement. An exchange of distributed documents will not be made.
Mounting instructions for Double Sheet Control
For a reliable function of double sheet control systems the correct mounting of the sensors is absolutely necessary.
Single sided and two sided pass through double sheet control systems have different requirements.
1. Single sided double sheet control with T-, P-, W- and PW-sensors
1.1 General notes
The single sided measurement with magnetic or eddy current sensors is always a contact measurement. The
sensors should sit perpendicular on the sheets to be controlled and fully touch the material. Uncontrolled air gaps
and the influence of poor magnetic conductors such as plastic reduce the performance of the sensors.
The measurement principle is based on the law of magnetism. The magnetic properties of the sheets and the
environment influence the measurement. Covering the sensor with Teflon in order to protect the sheet surface is
possible but reduces the performance of the sensor and is therefore not recommended.
Monitoring:
The modern control units of ROLAND can detect unwanted air gaps between the sensor and sheet surface. For
this purpose the under gauge switching threshold (TU) should be used and set larger than 80 percent. An air gap
reduces the measured value. If this value drops below the threshold, an under gauge condition is signaled at the
0-Sheet output. It is highly recommended that the PLC issues of fault signal signal and stops the process. Only
after elimination of this fault condition should the process continue.
Please observe:
The sensor should rest fully on the sheets to be controlled. No other material should hinder this contact. The
under gauge signal of the control unit has to be properly adjusted and the under gauge signal at the 0-Sheet
output must be analyzed!
Montag
Attention:
Air gaps can distort the measurement value. The same applies to a partial gaps - for instance in case the tilted
sensors or bowed sheets.
Warning: If these notices are not observed the
reliability of the operation cannot be warranted.
Sketch 1 shows the correct situation:
1
Correctly! The sensor touches
the sheet fully without an air gap
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The sketches 2 to 6 show faulty situations:
2
Faulty! The sensor does not
touch the sheet.
3
Faulty! The sensor does not sit
perpendicular on the sheet, sensor
bracket apparently not suitable.
4
Faulty! An air gap exists between the first
and the second sheet. The sensor is
mounted in an unfavorable position.
5
Faulty! An air gap exists between
the first and the second sheet. The
second sheet clings to the first
sheet, perhaps by stamping
residuals.
6
Faulty! Fault prone control in a bucket.
An air gap exists between bended
sheets.
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1.2 Magnetic and eddy current measurement principle
The magnetic conductivity of steel is about 1,000 to 2,000 times greater than the magnetic conductivity of air.
The magnetic conductivity is expressed by the „relative permeability“ µr. This means that air has a µr equal to 1
and regular steel has a µrsteel = 1000. Based on these physical properties it is immediately apparent that
undefined air gaps have to be avoided under all circumstances. Covering the sensor face with Teflon or similar
nonmagnetic materials is possible but not always a practical solution. Depending on the thickness of the
material this cover can reduce the measurement range substantially and thereby the maximum thickness of the
sheets to be controlled.
Roland Electronic uses the permanent magnetic principle (T-sensors) as well as be electromagnetic principle
(P- and P-part of the PW-sensor). The electromagnetic measurement system is more sensitive to air gaps than
the electromagnetic measurement.
Permanent magnetic sensors are used today practically only for thin sheets, for instance, for the control of tin
plate in the can making industry. The magnetic force of the permanent magnet has a tendency to move the
sensor into a perpendicular position to the sheet thereby reducing the probability of unwanted air gaps. Sensors
with rare earth permanent magnets allow small sensor bodies but have strong magnetic forces. They are wellsuited for applications like hidden parts detection (see figure 2).
The eddy current measurement principle for single sided double sheet control is not as sensitive as the
magnetic one regarding air gaps. Small air gaps (smaller than 1 mm) between the sensor and first sheet can
generally be tolerated. However, this statement is dependent on the sheet thickness and the electrical
conductivity of the material. For particular cases it may therefore be necessary to execute tests.
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1.3 Conditionally suitable: Flexible sensor bracket
When using P-, W-, and PW Sensors a flexible sensor bracket should be used instead of rigid assemblies. The
flexible sensor bracket allows the sensor to sit perpendicular on the sheet even if the assemblies are not
completely aligned. However, horizontal cable pull should be avoided because of the reduction of the positive
effect of springs. In addition the mounting should ensure that the springs cannot get stuck. Otherwise the sensor
may be presented tilted to the sheet. Ideally the flexible sensor bracket should be mounted in such a way that
the sensor is presented with pre-tension to the sheet. This ensure stable positioning of the sensor on the sheet
even under vibrating conditions.
Please observe:
A fixed sensor bracket is not suitable. Avoid horizontal cable pull when using flexible sensor brackets. The
lengths of the springs should be sufficient for the operation and mounted in such a way that they are never fully
compressed. The surrounding equipment should not interfere with the free movement of the springs.
Observe pre-tension!
Avoid horizontal cable pull in order to
minimize improper sensor presentation
6
Movable
57
Lift
max. 65
min. 25
98
6
Sensor
Counter lock
Figure 3: Spring loaded sensor bracket
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1.4 Not suitable: Bellows style vacuum suction cups
Other available vacuum suction cups of the bellows style have the advantage of lifting sheets which are tilted,
for instance, by spreader magnets. However, this advantage of lifting tilted sheets is a distinct disadvantage for
double sheet control because the sensor itself can tilt against the sheet surface as depicted in figure 4.
Improper presentation of
the sensor in case of tilted sheets
Figure 4: Advantages and disadvantages of harmonica style suction cups
In case the sensor is presented to tilted sheets the ROLAND double sheet control unit will signal an under
gauge condition. This is especially the case if the limit value is close to the nominal value, for instance 85 or 90
percent. This, however, is true for both the presence of single sheet or double sheet.
If it is known, for instance, through an additional part presence sensor that there is a sheet in front of the sensor,
then an under gauge signal indicates an improper sensor presentation. In general, this will be a tilted sensor
position or a not permissible air gap.
This under gauge signal should always be analyzed by the PLC and the machine controls as an important
indication of an improper sensor position. Other available control systems on the market do not differentiate
between under gauge and no sheet. In such cases it is not easy to detect improper functioning of a sensor.
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1.5 Well suited: Flexible sensor bracket with flat suction cup
The flexible sensor bracket with the flat suction cup is tried and proven solution. The proper presentation of P-,
W-, and PW-sensors is best achieved by this assembly.
The flat suction cup results in the low tilt moment and is the preferred solution. This flat style ensures that the
sensor is presented perpendicular to the sheet. The creation of sufficient vacuum is however necessary. For
proper functioning of the suction cup we recommend the use of Teflon tape on the thread of the sensor for air
tightness.
The suction cup should not be used as a lifting device. Otherwise the rubber lips may separate from the sheet
thereby causing a gap between sensor and sheet. In addition the sensor should be mounted in such a way into
the suction cup that the sensor surface is aligned properly to the inside rubber pad with the nipples.
Please observe:
The sensor surface should be properly aligned with the rubber pad (see detailed sketch). There should be
sufficient vacuum. The suction cup should not be used for lifting the sheet. This is best accomplished by the pretensioning of the springs.
Spring loaded sensor bracket
98
6
Sensor
6
57
Lift max. 65
min. 25
Movable
5
Counter lock
Detail view
Suction cup
110
Sensor
Suction cup
Rubber nipples
Sensor edge
Figure 5: Mounting of the sensor in a flat vacuum suction cup
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1.6 Improving the detection reliability in case of double sheet
Longtime experience has shown that the mechanical presentation of the sensor to the sheet is the most
important factor for a reliable double sheet control. In case of malfunction it is therefore recommended to start
with an analysis of the mechanical system. The comparison of the actual situation with the sketches in figure 1
can be a good starting point. In most cases of malfunction one or the other sketched situations is probably
present.
Sometimes it is not immediately visible that the sensor does not touch the sheet because the sensor is mounted
in a vacuum cup and the air gap is not immediately apparent. The checklist at the end of this paper should be
consulted before requesting the visit of a service technician.
If the machine cycle time and the machine design allow it, redundant measurements on the same part at
various places should be considered. Double Sheet Detector systems are available which allow the direct
connection of up to 4 sensors or even more with the Sensor Switch Box. This makes it possible to monitor with
several sensors in various places within a production cycle.
Another measure to improves the reliability is the use of a bigger sensor, for instance, instead of the P42GS the
bigger sensor P75GS. In the diagram below Figure 6 shows the permissible air gaps in the relation to sensor
size and sheet thickness. Bigger sensors are in a position to bridge bigger air gaps.
If the single-sided measurement does not lead to satisfactory results then the use of an additional two-sensor
pass through system should be considered – especially at a mounting position shortly before the tooling. Two
sensor systems can also be moved into the control position by means of a pneumatic cylinder.
maximum air gap between the sheets in mm
12
11
P 75 GS / P75 V GS (dotted line)
10
9
8
7
6
P 42 GS
5
4
3
2
P 36 GS
1
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
5,5
6
6,5
7
7,5
Sheet thickness in mm
Figure 6:
Permissible air gaps between the first and second sheet depending on sheet thickness and sensor size
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1.7 Measures to remove double sheet in case of one-sided measurement
If a double sheet is detected it various methods can be used to eliminate a double sheet situation. Below are
some examples:
- Oscillation
Figure 7.1: This can lead to the second sheet falling back into the stack
- Bending
Figure 7.2:
The movement of the suction cup and the double sheet and could result in the separation of the second sheet
- Dropping the sheets and lifting again
Figure 7.3: By falling back into the stack the double sheet can separate and therefore be lifted individually
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- Peeling
Peeling
Sensor
Sensor
Lifting with bended sheet
Figure 7.4: This measure is designed to peel off the sheet before lifting in order to avoid double sheet, but also
checks for double blanks in the bended position.
If these and other measures do not lead to the desired results, then it is necessary to remove the double sheet
either automatically or manually from the process.
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2. Non contact double sheet control with two-sensor systems S/E and MS/ME
Whenever possible a noncontact double sheet control with a two- sensor system should be used to check the
sheets. This can be made „on the fly“ or stationary. The two-sensor system offers many advantages in
comparison to single-sided measurement:
- The measurement is noncontact
- Measurement „on the fly“
- The sheets can move freely within the sensor gap
- Steel and nonferrous sheets can be monitored with the same sensor system.
However, when transporting ferromagnetic sheets on magnetic conveyors the leading edge generates a spike in
the sensor. The suppression of spikes requires special measures which are discussed later on.
Attention: In case of magnetic conveyors sepcial considerations apply.
2.1 Selection of suitable sensors
The most important parameters regarding the selection of suitable sensors are:
- The type of material, ferrous or non-ferrous material
- The sheet thickness range in mm or inch
- The desired air gap between sensors.
Sensor diagrams are available for each pair of sensors to more precisely describe the performance ranges.
Areas in the diagram (Figure 8) have been denoted with „Fe“ for ferrous material and „Al“ for non-ferrous
material. Aluminum with a conductivity value of 25 MilliSiemens has been selected as being representative for
non-ferrous material. This type of aluminum is considered typical for automotive sheet metal.
However, the conductivity value of non-ferrous material can very over a wide range as the following examples
show: non magnetic (Austenitic) stainless steel = 1.3; brass = 16; pure aluminum = 35; copper = 58. As a
general rule permissable sensor gaps get smaller and controllable material thickness gets thinner if the value of
electrical conductivity of the material increases. Because of the very many combinations regarding conductivity
and thicknesses it is not very practical to establish voluminous tables.In order to determine the precise
performance values of a pair of sensors a test with the materials to be controlled may be necessary. The areas
in the diagram below show the limits (the air gap between the sensors) where the sheet can vertically move
without creating a faulty switch signal.
Example (see next page):
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Sensor distance gap Ax
mm
120
Ax for Max 105
100
Pair of sensors S/E 54
Ax for Max 80
Ax
50
Al
Ax for Min 30
Fe
Ax for Min 10
0
0
1
0,7
2
3
4
5
6
7
8
9
Sheet thickness
10 mm
Figure 8: The sensor gap between transmitter and receiver depends on the type of material, sheet thickness
and sensor size.
Example:
Steel with the thickness of .7 mm has to be controlled for double sheet. The selected sensor pair S/E54 has an
outer diameter of 54 mm. The vertical line will cut the field for ferrous material at a sensor distance of 10 mm on
the minimum side and at 80 mm at the upper side. This means that the minimal distance Ax-between the
sensors can be 10 mm and a maximum distance between the sensors should not exceed 80 mm.
A sheet with a minimal size of three times the sensor diameter which means approximately 160 mm in diameter
would results in reliable double sheet control if properly calibrated. This means that single or double sheet can
be at any point in the sensor gap (flutter, vibrate) and still lead to reliable results.
For the sheet of .7 mm aluminum the selection or sizing is done the same way leading to a minimum distance
should of about 30 mm and the maximum distance between the sensors of about 105 mm.
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2.2 Functional principle of the pair of sensors and mounting
A working knowledge of the sensor principle is desirable. The sensor system functions according to the socalled transmission principle. This means the transmitter generates an electromagnetic field which in turn
generates eddy currents in the sheet to be monitored. The eddy current depends upon the sheet thickness and
the type of material. The Receiver measures the magnetic field generated eddy current which is correlated to
thickness. The sensors are unshielded, this means that the electromagnetic field is also horizontally active.
If the sensors are mounted into brackets made of material with high conductivity, for example, aluminum then
the sensor bracket absorbs a lot of energy from the sensors, thereby reducing the performance of the pair of
sensors substantially. For this reason mounting should be done in sturdy plastic. In case of steel it is
recommended that the sensors stick at least 10 mm out of the bracket. This may require additional protection
shields to prevent the sensor from being damaged by transfererd sheets.
Recessed mounting of the sensors in the brackets is, however, not recommended. Chips and dirt can
accumulate in these cavities and also reduce the performance of the system.
External shield
> 10 mm
In case of steel brackets,
sensors should stick out of
the bracket approximately
10 mm.
Flush mounting is
recommended for plastic
brackets.
Sheet feeding
> 10 mm
External shield
Figure 9: External shields to protect the sensor from transfered sheets
Please observe:
The mounting of the sensors should be made in such a
way that the measuring target is at least three times the
sensor diameter (x equals sensor diameter D; see
sketch). If this is not possible then it is however
necessary that the sheet is placed repeatably into the
same position for double sheet control. During the
Teach-in process the sheet should be in the identical
position horizontally and vertically as in the actual
production process.
t
ee
Sh
x
x
Sensor
D
Attention:
If the sheet does not cover the sensor fully then reliable double sheet control is only possible if the position of
the sheet horizontally and vertically is always identical to the Teach-in situation.
Warning:
If these instructions are ignored the process reliability cannot be warranted.
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2.3 Exchange of sensors
If the program parameters from the previous Teach-in should be used than please observe to the following:
1. Before moving the sensor, document the precise position in relation to the vertical alignment.
2. If Transmitter (S) and Receiver (E) are to be exchanged, then both positions need to be documented.
3. By exchanging the sensors the original alignment vertically and the relation to the gap between sensors
have to the be observed.
4. For the final adjustment (and control) of the gap between the sensors please use the sensor gap control
feature within the control unit I10. Details are found in the operating manual under chapter „configuration of
program parameters -- parameter sensor distance“
Attention: If the original sensor mounting cannot been re-created then the Teach-in of all program parameters
is necessary.
Warning: If these instructions are ignored the process reliability cannot be warranted.
2.4 Unfavorable mounting of sensors in magnetic conveyers
Figure 10 shows how holding magnets in conveyors not only generate a primary flux within the magnets and the
sheet but also secondary flux through the sheet. The magnetized sheets generate an induction voltage in the
receiver when the sheet moves in between the sensors. This blinds the system for about 60 milliseconds until
the induction voltage decreases to 0.
Conveyor rail
Primary
flux
Secondary flux
Conveyor rail
Transmitter
MS54S
N
N
S
NOT THIS WAY!
Faulty mounting of
holding magnets
The S-N magnetic pole
arrangement between
the conveyor rails create
a secondary flux.
Receiver
ME54S
Figure 10: Influence of the law of induction on double sheet control in magnetic conveyors
S
Primary
flux
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2.4.1 MS - Sensors
For the use in magnetic conveyors special sensors have been developed. In comparison to standard sensors
these so-called MS- sensors show an increased immunity against this specific noise generated by magnetic
conveyors. However the influence of the noise can be so strong that the simple use of MS sensors is not
sufficient. Under these circumstances the following additional measures can improve the situation.
2.4.2 Sufficient size of sensor target
In this case the requirements for covering the sensor fully are especially important (see chapter 2.2).
2.4.3 Measurement start between entering and exiting the sheet in the sensor gap
As a result of the magnetic field a large voltage spike is induced by entering and exiting the sensor gap. This
can result in a double sheet signal even if no double sheet is present.
Here it is best if the signal „measurement start“ is issued by the PLC when the sheet is already within the
sensor gap. Because the PLC cannot exactly locate the sheet during transport it is best to use entry and exit
proximity switches for the precise determination of the position of the sheet.
2.4.4 Mounting of in the Receiver between the magnets of the conveyor
Occasionally the mounting of the Receiver between the magnets results is an improvement. The gap between
the Receiver and the sheet should be approximately 5...8 mm. This leads to a gap between sheet and
Transmitter of about 25... 22 mm. The right position is however always depending on the geometry and
alignment of the magnets. If this information is not available then it should be determined by a test.
2.4.5 Equipment specific software
In especially difficult cases please contact ROLAND electronic. Sometimes specific Double Sheet Detector
software can be used. I10 control units starting with software version 27 have a special correction function for
magnetic noise generators.
Attention:
In case of magnetic conveyers observing the requirements for the measurement target are of outmost
importance. It is necessary that the position of the sheet is identical during Teach-in and in the production
process.
Warning:
If these instructions are ignored the process reliability cannot be warranted.
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2.5 Correct sensor mounting in magnetic conveyors
Mounting of the sensors according to figure 11 results in reliable double sheet control according to all available
experience. It is important that the holding magnets are mounted in such a fashion that no secondary magnetic
flux results between the conveyor belts either through the air (and through the sensor) or through the sheet
between the sensors. In this case it does not matter whether we have between the conveyors a situation
N <--> N or S <--> S.
The sensors should not be mounted close to the magnets but in the largest possible distance between the rails.
The brackets should be made of plastic or steel. Aluminum or materials with high electrical conduction dampen
the effectiveness of the sensors and reduce the performance.
No
secondary flux
Conveyor
Primary
flux
S
Conveyor
Transmitter
MS54S
N
N
S
Primary
flux
Ax <= 30mm
Use plastic brackets with a
cap of about 3 mm to
prevent bending sheets
damaging the sensor
Receiver
ME54S *
* Depending on the design of
the magnetic conveyor system
exchanging the positions of
transmitter and receiver could
improve results. In case of
questions please contact the
Roland Company.
Figure 11: Recommended mounting of holding magnets
S
N
S
N
No secondary flux
N
S
N
S
Preferably no magnets
in this area
Top view
S
N
N
S
S
N
N
S
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Checklist: One-sided measurement
YES
NO

2. Interface problems and electrical causes
- measurement results are interrogated before the measurement is finished.
- the under gauge condition is not monitored

3. Use of unsuitable cable
- wrong lead cross-section
- not shielded
- unsuitable in-line connector

1.Faults due to mechanical reasons
Is there an air gap between sensor and first sheet
- because of horizontal pull on the cable
- in the spring loaded sensor bracket
- in the vacuum cup
- because the vacuum cup is being used as lifting device
This sensor is mounted in a place where air gaps can develop
between the first and the second sheet, for example
- by partial separation of the double sheet (Fig. 1.4)
- the double sheet has separated in the middle of the blank
where the sensor is located (Fig. 1.5)
- double sheet control is performed in a bucket. The sensor bracket is fixed and
the sheets are bend so that air gaps can develop. (Fig. 1.6)
The faults description in the operating manual gives additional information
about causes of malfunctions.
Checklist: Two-sided measurement
1. Faults due to mechanical reasons
- Sensor coverage not sufficient resp. not constant
- the sensor gaps are different from those prescribed in the sensor diagrams
- the sensor bracket is made of material with high electrical conductivity values
for instance aluminum
- the sensor gap monitoring feature is not activated
- magnetic conveyors transports narrow sheets (smaller than 300 mm) with
high velocity (higher than 2 meters per second).
- the measurement time is not sufficient
- the holding magnets in the magnetic conveyers generate a secondary
magnetic flux in the sheet in between the conveyor belts.
- the sheet has a position in the sensor gap during Teach-in which is
different from the production conditions