Peter Nachtwey

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About Peter Nachtwey

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  • Location Vancouver, WA
  • Country United States
  • Interests Motion Control, biking, hiking, sailing, software.

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  1. CLX Rate of Change AOI? It is critical that the sample intervals be constant. Timers are not very good for this. Interrupts are much better.
  2. The statements above are correct. It depends on the process and it is a calculus problem BUT one doesn't need to know calculus if you know Laplace transforms. Laplace transforms are a way of doing calculus and differential equations using algebra. Basically there are two general type of processes. 1. Type 0 or non-integrating process. These are processes where the process value will return to steady state or ambient if control power is turned off. These are processes like temperature control or speed control. These are usually simpler to control and don't need a derivative gain. 2. Type 1 or integrating processes. These are processes that integrate the control output. Tank level control integrates flow and position control integrates velocity. In theory these processes don't require an integrator but do require a derivative gain. The reality is that these processes are never perfect so an integrator gain is required along with the derivative gain. There is a general rule. There should be one controller gain for every open loop pole in the process. The integrator gains doesn't count because it comes with its own pole. I know I just lost everyone with this statement but it is true and if you want know the truth before you die you should look into this. ( add it to your bucket list ). If you want to learn more you should look up topics such a pole placement or lambda tuning. I deal with calculus and differential equations just about every day so the math is no strain on my brain.
  3. OSR instruction in ST language

    ST has a built in FB called F_TRIG and R_TRIG. You must instantiate an instances of F_TRIG or R_TRIG for every one shot.
  4. MO2AE Gearing

    This was my first motion control application back in 1983. I had to slow the upstream lug chain down for one lug to make space for a cut into. Doing two or more cut in two in a row should be a problem. See this. My back ground is the saw mill industry. I worked for Applied Theory which is now part of USNR.
  5. Fighting the Flab

    We play table tennis. I have this just outside my office. That is a TT robot in the fore ground. We are good enough that we actually use all that space. I play about 10 hours a week. That keeps the lbs off.
  6. This usually happens when you divide by zero. This error can also happen when one divides a 32 bit number by a 16 bit number but the result won't fit into a 16 bit number. Then these errors occur an interrupt occurs where the designer either puts in a good error handler or simply reports the problem.
  7. Pressure Ramping With ON/OFF Valve

    I would use sliding mode control. Sliding Mode Control is good for those applications where the control mechanism is a simple on off device. You really shouldn't need a PID. Just turn on and off the valve depending whether you are above or below the target. The sliding mode control simply adds a rate control or prediction feature to the simple on off technique. This prediction technique would keep the rate from dropping too fast a the beginning.
  8. Realtime motion control

    The PLC can communicate with the motion controller fast enough to do most things. Usually the motion controller does all the motion control and the PLC simply issues commands or tells the motion controller when to execute user programs in the RMC motion controller. The motion controller has 64 MB of ram which is more than the PLC has. There are examples here:
  9. Sign Wave motion of linear actuator

    Our RMC100 has a stepper output module. It can generate sinusoidal motion profiles as well as point to point moves with s-curves. I think it would be better to stick with analog control. Then there are more options.
  10. Sine Wave motion

    We have a motion controller that can generate sine waves and we have a stepper motor output. See the step and direction, QST, module.
  11. PID Tuning Dilema

    From what Bob says it isn't that simple. The water must heat the surrounding metal too.
  12. PID Tuning Dilema

    The designers should be fired. I see to many systems that are designed without a thought as to how they are going to be controlled. Sure they can be controlled but all the extra effort often cost more than simply designing the system right in the first place.
  13. PID Tuning Dilema

    It looks like a few of us have come up with the same bias idea. I don't see why the temperature isn't exact almost immediately if there is no water in the vessel to start with.
  14. PID Tuning Dilema

    I am always watching. I would bias the PID with an offset of 100*(120-70)/(140-70)% control output. It can be even more accurate if you know the exact hot and tepid temperatures. I chose 70 as the average tepid temperature and 140 as the average hot temperature. You should be able to get by with just a P gain but using the integrator will help make the time constant precise. If you want the to get with 1% of 120 degrees in 120 seconds the integrator time constant must be about 24 seconds. An exponential process will get with 1% in 5 time constants and 5 times 24 = 120 seconds. It would be good to know what you are using for your gains. Do you understand how I calculated the bias?
  15. speed calculation from encoder position

    You really should get a M02AE and an encoder that provides MUCH higher resolution. What you have will not work unless your positioning requirements are very lax.