1 Backiron[edit | edit source]
The backiron compensates the magnetic pull on a driven clip, in the area where motors are mounted on the bottom level only. Otherwise the forces on the roller bearings are too high, which leads to a short lifetime. The backirons for 0idler and 2ilder lines consist of metal sheet in a rectangular shape, for 1 idler lines in shape of the motor iron core. Furthermore the 1idler backirons are covered with a stainless steel housing, in order to avoid dirt inside the grooves and make the whole construction more rigid.
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backiron - CAD
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backiron
2 Clips[edit | edit source]
A clip clamps the edge of the film and applies the stretching force.
2.1 Different clips[edit | edit source]
There are different types of clips, but the main difference is a driven or an idler clip. A driven clip has the secondary part, a permanent magnet system, on its top and bottom side. The driven clips applying the stretching force (MD and TD direction) on the film, caused by the longitudinal magnet wave of the linear motor. The idler clips applying a stretching force only in TD direction, no permanent magnet system is mounted. On the idler clip the brake plate of the idler brake is mounted.
For every line type, 0idler, 1idler and 2 idler, exists a different permanent magnet system. The 0idler magnet system consists of one symmetric pole pair. There is a shift of 1/6 lambda between top and bottom magnet system. The 1idler magnet system consists of two asymmetric pole pairs, no shift between top and bottom magnet system. The 2 idler magnet system consists also of two pole pairs, but in a symmetric order. There is also no shift between top and bottom magnet system.
In every line exists at least one and up to 3 index clips. The index clip is a driven clip with switch cam on its backside. The switch cam is tripping the FDM sensors for counting. In order to identify the index clip easier, the clip body is silver coloured.
2.2 Clip layout in transport system[edit | edit source]
The amount of idler clips between two driven clips has to be always constant. But number of idler is depending on the line type, 0idler, 1idler or 2idler. The whole amount of clips depending on the length of the track system and will be defined during the design process.
The distance between the index clips has to be bigger than the length of the preheat zone. In order to identify which index clip is passing a FDM sensor the distance between the index clips should not be equal.
To make sure that the clip order is correct, a list is very useful. In addition the list can be used to notice the serial number of the clips. Later on this is very important for the maintenance of the clips.
2.3 Clips in PH[edit | edit source]
Inside the preheat zone the elastic bumpers are compressed and the distance between two clips has to be the exact clip spacing (clips in stack). To make sure that the clip spacing is always constant, the number of clips in the preheat zone is counted. To make sure, that the automatic counting is working proper, it should be checked a few times during the checkup by manually counting. To make sure that it works correct the distance between the two FDM-sensors, which are responsible for the counting, is always a multiple of the distance between two driven.
3 Idler brakes[edit | edit source]
The idler brake is an eddy current brake. The brake plate is mounted on the backside of the idler clips and the permanent magnets are mounted between the top motors and the clip rail. The permanent magnets are in the area of the line where a deceleration of the clips is necessary and no film is gripped. During the deceleration process the idler brakes make sure that the idler clips are always in contact with the driven clips. This would be the perfect operating situation.
But the breaking force is depending on the line speed and the air gap between breaking plate and permanent magnets (small gap -> high break force; big gap -> low break force). So a perfect adjustment is only possible for one operating point. The air gap has to be adjusted to values that the driven and idler clips stay as long as possible in contact during the deceleration process for every possible line speed and deceleration rate. If the idler clip loses the contact to the driven clip, it is not allowed that the idler clip hit the previous driven clip. The time when the idler clip loses to contact to the driven clip should be as short as possible. Losing contact leads always to a more or less strong collision, which causes an oscillation in the system. The collision can be so strong that the driven falls out of the magnetic wave.
But the air gap should also be not too small because this may lead to a breaking force which is higher than the force of the driven clip and the clip falls also out of the magnetic wave.
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position of idler brakes permanent magnets
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air gap of idler brakes - CAD
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air gap of idler brakes
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idler brakes
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idler brakes - front
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idler brakes with clip
4 FDM sensors[edit | edit source]
The FDM sensors (force displacement monitoring) are inductive proximity switches. These sensors are used to compare set and actual position and counting clips in the preheat zone. The gap between switch cam and FDM sensor should be not wider than 1mm. During the adjustment it must be regarded, that there is a mechanical clearance of the clip in the track system. So if a clip is pulling a film, the position of the switch cam may be different. The adjustment has to make sure that under every condition the gap is not to small and no collision occurs.
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position of FDM sensors
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FDM sensor position - FOK 7.1
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FDM sensors in preheat - counting and position
There are mounted two sensors at the same position inside the preheat zone. The lower ones are used for counting the clips in the preheat zone and the upper ones are used to compare set and act position. The other ones, mounted before smart drive 1 and smart drive 2, are used to compare set and act position before the clips are entering the smart drive. The values of the sensors in the preheat zone create a reaction of the linear motors during the initialisation process, later on they only observe the correct initialisation (in case of fault they restart the initialisation process) while the line is running. The sensors on the smart drives always create a reaction, but until now they are not used because due to the more rigid BMS04 system they are not needed. All functions are described more in detail in "20. Running line".
5 Inlet speed encoder[edit | edit source]
On the LISIM inlet, after the clip closer, are mounted two measuring wheels which are mounted on rotary encoders. The wheels are measuring the actual speed of the line, because they are in contact with the cast film. The measured speed is used for a feed forward and a feed backward control to reduce the jerking of the cast film. Until now the control is not activated, because the motor shift in the preheat zone and the reduced cogging forces of the BMS04, are leading to a tolerable inlet speed variation level.
For a later use the function of the encoder should be tested. The easiest way is to turn the wheel in film direction. Then the UP LED on the X20 counter module should be illuminated. Against the film direction, the DN LED.
6 Flap and clip control[edit | edit source]
There are two types of sensors inside the LISIM track to ensure the machine safety of the line. One type is called the flap control, the other type is called clip control. The clip control is similar to the sequential lines. If there is remaining film inside the clips after the clip cleaner, the clip control safety switch made sure that no film will be transported into the return side.
The flap controls make sure, that no film will be transported into the clip opener or clip closer. I could be possible, that film is wrapped around the clip knife and will be squeezed in the air gap of the clip opener or clip closer and damage them. The flap control is mounted on the return side before the LIM wheel and a few meters before the outlet, in the area of the neutral zone.
During the checkup, the gap between flap and clip knife needs to be tested. It could also be possible, that the first heat up of to oven reduces the air gap. In this case a new adjustment is necessary.
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flap control - CAD
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flap control
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clip control
7 LIM wheel[edit | edit source]
The LIM wheel is working like an induction motor. In the LIM wheel a stack will be created, this is a clip buffer in the asynchronous part of the line. This buffer is necessary to provide clips on the LISIM inlet when they are needed, e.g. a few clips fell out of the wave in the transport zone, clips out of the wave during film thread or a transition is running. To create a stack, the clips are moved to the minimal possible MDX at the end of smart drive 2. When the clips are leaving the smart drive 2, they entering the LIM wheel and due to the LIM wheel over speed they will be in stack under the LIM wheel.
To create a stack the LIM wheel has to run at an overspeed. This overspeed has to be evaluated during the checkup.
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LIM wheel
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LIM wheel - overspeed
There are two different LimWheel types. The 7.4 type with a gearbox and the 7.1 type with a direct drive. Following a screenshot from the two configuration possibilities.
8 motor and drive cooling[edit | edit source]
The linear motors BMS04 and the B&R inverters are water cooled. To provide a clean and proper cooling water, there are two separate cooling circuits. This cooling circuits are also separated from the customer water. They are connected via a heat exchanger to the tower water. The flow temperature should never be above 30°C, otherwise a proper cooling is not possible.
The cooling for the B&R inverters is called the drive cooling. The inverters are mounted on a cooling plate. The flow per cooling plate is maximum 6 l/min. A flow of 5 l/min per cooling plate should be adjusted. It is possible that two or more cooling plates are connected parallel, so the flow has to be adjusted to 10 l/min respectively 15 l/min.
At the motor cooling a certain amount of motors is connected parallel via a collecting pipe to one supply. The flow for one motor inside the oven should be 5 l/min, on the returnside outside the oven 3 l/min. The flow of 5 l/min per motor is the maximum, never exceed this value.
There are PI diagramms for both cooling circuits where the correct flow for each supply, respectively flow switch, is defined. By checking how many cooling plates of motors are connected parallel the values from the PI diagramm can be double checked.
The alarm trigger level of the flow switches has to be set at aprox. 50% of the flow. Below that value a proper cooling can not be guaranteed.
For the two main circuits the max. allowed pressure is 6 bar. With a complete closed bypass this value should never be exceeded.
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motor and drive cooling - PVSS screenshot
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flow switches motor cooling
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motor cooling collecting pipe
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flow adjustment
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flow sensor
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bypass
