Need Temposonic Rod Scaling Help
Need Temposonic Rod Scaling Help
(OP)
Have a 130" temposonic rod to keep track of press position.
Using Siemens PLC 555. Rod is an MTS Flexible Sensor, 0-20ma @ +24vdc. MTS 201554 magnet. Not too sure how the scaling functions work. Need some advise please.
thanks
Using Siemens PLC 555. Rod is an MTS Flexible Sensor, 0-20ma @ +24vdc. MTS 201554 magnet. Not too sure how the scaling functions work. Need some advise please.
thanks





RE: Need Temposonic Rod Scaling Help
Do you have a part number for the one you are having problems with?
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Sometimes I only open my mouth to swap feet...
RE: Need Temposonic Rod Scaling Help
You need to provide the A to D counts and position at two extremes of the rod.
Then it is a simple matter of calculating m and b for y=mx+b. Isn't there a scaling block in the TI PLC?
BTW, I deal with Balluff and Temposonic rods all the time. They are roughly the same. I also get involved with a lot of presses. PLCs work some times but the motion control is crude. It looks like this press can open wide which means that it will want to move quickly to close. This is another trick. The velocity at which one makes contact with the work piece is critical. One want to match the kinetic energy of the press with the work required to form the piece as closely as possible. Too much kinetic energy results in pressure spikes and too little requires the press to build up pressure slowly ( slow production ) to form the piece and even then the piece may not be formed right. Since the kinetic energy is proportional to the velocity squared one can see the good speed control is critical. The point is that it is difficult to get could speed control with the resolution possible from an A to D card or the asynchronous nature of the MDT rod updates and the PLC scan. One should really get a controller that can directly interface to a MDT rod either using start/stop or an SSI feedback.
RE: Need Temposonic Rod Scaling Help
What is your experience of the digital interface Balluff (or Temposonics) transducers? Sounds fairly good for a system requiring a fast loop response. I looked at them a while ago for fitting to a steam turbine but I wasn't prepared to put the processing electronics in the hostile environment of the turbine-generator if I could avoid it and the distance to the turbine controller was long so it was 4-20mA on that job. I am interested in the SSI type for future applications though. I have been using the US version of the BTL-5 explosion proof transducer where it has proved almost impregnable to mechanical damage, and resistant to process fluids and environmental contaminants. Pricey, but this industry can't afford downtime.
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Sometimes I only open my mouth to swap feet...
RE: Need Temposonic Rod Scaling Help
I prefer the start/stop interface or the SSI. Start/stop is the basic or native interface. The rods will naturally do start/stop. I like this interface because I know there is nothing between the motion controller and the data coming back. SSI provides more resolution at a slightly higher cost. What I like about SSI from a practical point of view is that there is no need for a gradient. All 5 micron rods are the same in theory so one can change on out for another without changing the scale factor. One must be careful to screw in replacement rods the same number of turns as the old rods so the offset remains the same. Otherwise a new offset must be determined.
I dislike analog rods for motion control. That includes presses. Hint. The problem is that analog signals are noisy and drift but the worse part is that the motion controller or PLC doesn't know when the data was valid. It is very important to know not only the position but the time at which the position is valid. This rules out analog rods because the start pulses are initiated by the rod itself and not the motion controller. I can go into this in more detail. The simplest interface is the start/stop interface. The motion controller sends the start pulse every millisecond or half millisecond. We use a FPGA, field programmable gate arrays, to do this because interrupts have jitter that causes velocity errors. There can be no software involved with the timing. We use a 240 Mhz counter that will provide about 0.00045 inches or 12 micron resolution. We use observers to provide excellent velocity and acceleration feedback data. The SSI rods convert the time between the start and stop pulses to a digital number that represents the position. Initially I had problems with both Temposonics and Balluff because they would claim 5 micro resolution but the rod update was asynchronous to the controller. This means if the actuator is moving 1 m/s it is moving 1mm/msec. I would have a 5 micro position that was valid anywhere within the millisecond which essentially meant I had 1mm resolution at high speed. This has all be fixed now but Temposonic and Balluff don't synchronize the positions to the controller in quite the same way so there are differences in the quality of feedback. Our motion controller can graph the data from the rod a plot it. My favorite test is the drop test. I point the rod up and drop the magnet. I should see a smooth acceleration due to gravity.
I/we have worked with both Temposonic and Balluff for many years. We try to stay neutral. Both companies have their advantages and disadvantages. I have see both screw up big time and other times do very well.
If you have more questions just ask here or see
www.deltamotion.com.
RE: Need Temposonic Rod Scaling Help
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Need Temposonic Rod Scaling Help
RE: Need Temposonic Rod Scaling Help
One must be prepared to adjust the offset. A press will "warm up" and the offset will change as function of the metal expanding.
RE: Need Temposonic Rod Scaling Help
How fast is the approach to the target, and how is the loop tuned? A critically damped loop will see some overshoot. Could this be a servo tuning problem rather than a problem with the feedback?
Also consider that reliably resolving 20 thou in a 130" travel is approaching the limit for a 16 bit DAC. How good is the DAC fitted to the Siemens PLC I/O channel?
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Sometimes I only open my mouth to swap feet...
RE: Need Temposonic Rod Scaling Help
I appreciate your replies.
RE: Need Temposonic Rod Scaling Help
If so then I don't think this is a scaling problem. I think it is a mounting problem. Is the problem rod mounted differently than the good rod? Have you tried using a dial indicator. .020 inches is a lot.
A PID will not cure a feed back problem.
Are both rods using the same analog input card?
It is time for you to start telling us about all the things that are different between the rods. Mounting, location, power supplies, wiring, anything. You should be thinking about what causes a difference, any difference.
So far you have not said this is a control issue.
[OT]
"A critically damped loop will see some overshoot."
No it shouldn't! Under damped systems over shoot. Critically damped system aproach the set point exponentially. However this requires the proper form of PID and that usually isn't available on a PLC. The problem is caused by the zeros introduced by the P and D gains in the forward path. Another form of PID is the I-PD where the P and D terms are only in the feed back path and therefore dont add zeros. I-PDs can be tuned so they don't over shoot. What one give up is bandwidth.
Ask about this on another thread in the control section. I have graphs and Bode plots that show the differences between PID, PI-D and I-PD
[/OT]
Peter Nachtwey
RE: Need Temposonic Rod Scaling Help
I do not believe I have a control issue or even feed back at that. I think it is more of an linearity performance problem. At 125 inch rod set at 1 recirc is about the best I am going to do. So I think at 0.02% times the length of the rod is going to give me 0.025, which about the swing I am seeing.
Thanks again. You were a big help.