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servo amp and servo controller

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Sep 29, 2002
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lm628 driver lpt

What is difference between servo amp and servo controller? I have a 4800rpm dc servo motor and 2000cpr encoder, how can i build a simple linear interpolating system via pc? I wanna design my own servo amp and controller.

cnc lm628 lm629

In general, the amplifier is what applies power to the motor in proportion to its input signal. The controller is the whole feedback system. You are in for a complex time. There are whole books written on sampled data control systems. Unless you are able to measure all of the physical constants (inertia, various power law frictions, torque, backlash, etc.) and compensate for them, you will end up with such a low loop bandwidth to force stability that the motor will not respond as rapidly as you want.

hmm, i looked data control systems books at and they are expensive for a student. Do you know ebook about sampled data control systems?


I do not know of any ebooks, but your other two alternatives are the library and used books. This site

is a search engine that searches web sites that sell used books.

servo amp: power driver electronics for servo motors.
servo controller: this systems have command and error inputs and produce control signal for servo amplifier.

you can begin with Natinal LM628-LM629.

You also can look at HCTL1100 specifications from HP. If I'm not wrong this chip can be found in the older models of deskjet printers

LM628 and LM629 are PID controller for DC motor.

The goal is to :

-get data from optical coder (position)
-generate a command (PWM or tension) by a PID (on the difference between optical coder position and consigne)

We've made a web page (sorry, it's in french) on the use of LM629

Thanks a lot! I don't know French but i downloaded datasheets from national web site.

Where can i find some ebooks about servo control? thanks a lot.

Hi Battle,
I downloaded "Automatic Control System and Components" ebook from ebook section and there are good resources at -> w*
and if you could find any useful resources please pm me.


For designing a servo amp: search Google with keywords "IR2110, H-bridge, PWM etc.".

Software for PC: search for "Yeager CNC Pro, TurboCNC, Linux EMC etc.".

Rutex has some nice chips and servo amps/controllers that work well with common PC software that are designed for stepper control. Servos are smoother and cheaper than servos, that's why the tendency is nowadays to use servo controllers with step/dir pulse interface for position control.

You'll need for example:
- A counter that counts the step/dir signals from LPT
- A counter that counts the motor's encoder pulses
- An adder that subtracts the latter from the former
- A DAC for analogue output: 0...10 volts: 5 volts means standstill, or -10...+10 volts: 0 volts means standstill.
- A PWM generator and PID filter: voltage in, PWM out. In one system 50% PWM signal to servo amp results in standstill; less than 50% and the motor runs backwards, more than 50% and the motor runs forward.

It's not very complicated, but perhaps I presented it in a complicated manner... ;)


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