PCIx Specifications - Pro-Dex, Oregon Micro Systems - #15

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GETTING STARTED TUNE THE SYSTEM PCIx User’s Manual 2-9 d. If the response is negative, your encoder must be reversed. i) If your encoder produces a differential signal, swap Phase B with Phase B-not and repeat from step (a.) above. ii) If your encoder produces a single-ended (or TTL) signal, swap Phase A with Phase B and repeat from step (a.) above. e. If the RE response is still negative, contact Pro-Dex, Inc., Oregon Micro Systems, Technical Support for assistance. 6. Repeat from step 1 for the other servo axes. 7. Remember to set DZ and KO for each axis at every power-up unless you store the values in Flash (See AP command). NOTE: Most encoder problems are caused by lack of power or incorrect connections. If the encoder position changes by only 1 count, this is an indication that one of the phases is not connected. Do not proceed until you perform all the steps in this procedure, ensure that the outputs of the PCIx are as described and ensure that the encoder is operating correctly 2.7. TUNE THE SYSTEM 2.7.1. INTRODUCTION The following is an introduction to tuning a servo motor and the basics of the process. Tuning a servo system is the process of balancing three primary gain values P, I and D in order to achieve optimum system performance. In a closed loop system, an error signal is derived, amplified, then supplied to the motor to correct any error. Clearly, if a system is to compensate for infinitely small errors, the gain of the amplifier needs to be infinite. Real world amplifiers do not possess infinite gain; therefore, there is some minimal error which cannot be corrected. The three primary gain values used in servo systems are P (proportional), I (integral) and D (derivative). The "P" term is used as a straight gain factor to get the system response "in the ballpark." The "I" term defines how quickly the system will respond to change. The "D" term determines the system's stability. This term defines how quickly the system settles at its desired position without oscillating. The effects of these parameters can be seen when looking at the system’s response to a step change at the input. The shape of the step response falls into one of three categories: under damped, critically damped or over damped. Over damped systems are slow to reach their final value and produce little or no oscillation. Critically damped systems reach final value quickly, without overshoot. Under damped systems reach final value quickly, but have various degrees of “ringing”, or oscillation, that decay to zero over time. Ideally, a system should be critically damped, allowing for the fastest response time with the least amount of oscillation.