DC servo motor with optical encoder

i'm replace stepper motor dc servo motor optical encoder. of pid-library br3ttb (http://www.arduino.cc/playground/code/pidlibrary) able control either velocity or position of motor.

the real challenge @ moment, me, control both velocity , position. more want to:

1.) ramp velocity @ start;
2.) keep velocity constant;
3.) ramp down velocity before given position;
4.) , hold given position whatever happens.

if understand correctly should use 'cascade control' (http:// http://en.wikipedia.org/wiki/pid_controller#cascade_control); using 2 pids arranged 1 pid controlling set point of another. however, interpretation not working should. ideas?

code: [select]

#include <avr/interrupt.h>
#include <pid_beta6.h>

#define encoderpina 3    //quadrature track (interrupt 1)
#define encoderpinb 4    //quadrature track b
#define outputpin 11

volatile long encoderpos = 0;
long encoderpos0 = 0;
unsigned long time = 0;
unsigned long time0 = 0;
int rpm = 0;
int error = 0;

double displacementsetpoint, displacementinput, displacementoutput;
pid displacementpid(&displacementinput, &displacementoutput, &displacementsetpoint, 2,3,0);

double velocitysetpoint, velocityinput, velocityoutput;
pid velocitypid(&velocityinput, &velocityoutput, &velocitysetpoint, 2,3,0);


void setup(){
 pinmode(encoderpina, input);
 digitalwrite(encoderpina, high);    // turn on pullup resistor
 pinmode(encoderpinb, input);
 digitalwrite(encoderpinb, high);    // turn on pullup resistor

 attachinterrupt(1, doencoder, change);    // encoder track on interrupt 1 (pin 3)

 displacementpid.setmode(auto);
 velocitypid.setmode(auto);

 beginserial(115200);
}

void loop(){
 time = micros();

 rpm = 60 * 1000000 * abs(encoderpos - encoderpos0) / ((time - time0) * 2000);
 error = 100 * (rpm - velocitysetpoint) / velocitysetpoint;

 encoderpos0 = encoderpos;
 time0 = time;
 
 displacementsetpoint = 30000;                        // position
 displacementinput = encoderpos;                  // read input interrupt
 displacementpid.compute();                        // calculate magic number
 velocitysetpoint = displacementoutput;      // use output set point velocity (?)
 velocityinput = rpm;                                    // input rpm calculation
 velocitypid.compute();                              // calculate output
 analogwrite(outputpin,velocityoutput);      // use velocityoutput
}

void doencoder(){    //every time change happens on encoder pin doencoder run.
 if (digitalread(encoderpina) == high) {    // found low-to-high on channel a
   if (digitalread(encoderpinb) == low) {    //ccw
     encoderpos = (encoderpos - 1);
   }
   else {    //cw
     encoderpos = (encoderpos + 1);
   }
 }
 else {    //found high-to-low on channel a
   if (digitalread(encoderpinb) == low) {    //cw
     encoderpos = (encoderpos + 1);
   }
   else {    //ccw
     encoderpos = (encoderpos - 1);
   }
 }
}



hi, im quite interested know if got work , problem was?

thanks

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