Editing Servo tuning basics
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− | + | Driving a servo motor is much like driving a car. Driving a car has many similarities including the key concepts of torque, velocity and position control. Most of this happens in the driver's head the same way than a servo drive does with a motor. | |
− | + | ==Driving (a.k.a servoing) a car== | |
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− | ==Driving (a.k.a servoing) a car== | + | |
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[[File:Carexample base.png|800px]] | [[File:Carexample base.png|800px]] | ||
− | + | ==Driver as a controller== | |
− | + | ===What is a feedback gain and PI controller=== | |
− | + | Feedback gain means '''sensitivity to change output''' due to ''tracking error'' (the difference between setpoint and feedback). | |
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− | + | The simplest form of feedback controller is a '''proportional''' gain controller (P controller) where output follows the formula ''output = Pgain*(setpoint-feedback)''. The problem of proportional gain controller is that it may never reach the setpoint because output starts approaching zero when the following error is reaching zero. | |
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− | The simplest form of feedback | + | |
Because of this, it's better to add in '''integrating''' component to the controller (forming PI controller). Integrator accumulates the tracking error to a integrator variable. Integrator variable is like a bucket of water, when you add water, the water level rises and when you take out water, the level lowers. In controller the equation becomes: ''output = Pgain*(setpoint-feedback) + Igain*IntegralOf(setpoint-feedback)''. | Because of this, it's better to add in '''integrating''' component to the controller (forming PI controller). Integrator accumulates the tracking error to a integrator variable. Integrator variable is like a bucket of water, when you add water, the water level rises and when you take out water, the level lowers. In controller the equation becomes: ''output = Pgain*(setpoint-feedback) + Igain*IntegralOf(setpoint-feedback)''. | ||
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*I-gain - reacts slowly over time, adjusts output until tracking error is zero | *I-gain - reacts slowly over time, adjusts output until tracking error is zero | ||
− | When driving a car, human brain closely resembles the operation of a PI controller | + | When driving a car, human brain closely resembles the operation of a PI controller. |
− | + | ===Low feedback gains - sluggish response=== | |
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− | ===Low gains - sluggish response=== | + | |
[[File:Carexample sluggish.png|800px]] | [[File:Carexample sluggish.png|800px]] | ||
− | + | ===Too high feedback gains - oscillation & instability=== | |
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− | ===Too high gains - oscillation & instability=== | + | |
[[File:Carexample unstablepng.png|800px]] | [[File:Carexample unstablepng.png|800px]] | ||
− | + | ===Optimum feedback gains - only little overshoot=== | |
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− | ===Optimum gains - only little overshoot=== | + | |
[[File:Carexample stable.png|800px]] | [[File:Carexample stable.png|800px]] | ||
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===Optimum gains with realistic setpoint - optimum response=== | ===Optimum gains with realistic setpoint - optimum response=== | ||
[[File:Carexample response accellimit.png|800px]] | [[File:Carexample response accellimit.png|800px]] | ||
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