I am working on a project where I have to pulse a laser against a spinning, six sided polygon mirror motor.
https://www.precisionroller.com/motors-for-sharp-mx-3640n/products.html
(worth noting that i have them from china)
I am pulsing at the motor frequency x6 to get a single laser dot reflected of the mirrors.
The motor is receiving a PWM signal from an Arduino. The laser is receiving a 6x that frequency signal with a very small duty cycle.
For this I am using code that generates very precise pwn signals using ticks of the internal PWM clock. The signals are verified on my scope and are constant and in sync.
So far so good. I am getting my desired laser dot in the target area.
The problem is that the dot is wobbling back and forth.
I am on this project with a colleague who helped with all of this and made this video for him.
laser wobble
We cant figure out why that wobble happens.
These motors are used in laser printers and scanners and must spin with high precision.
We tried all kinds of things to make it steady. Hence the custom code for the PWM signals.
I have tried:
Is the motor broken? But all three of them?
Is it air turbulence? But that is also hard to believe since these motors sit in open spaces inside printers. If anything, then air turbulence would be worse in there.
Any tips on what that could be are well appreciated
This is the code we are using to create both PWM signals:
and this is temerhelpers.h:
https://www.precisionroller.com/motors-for-sharp-mx-3640n/products.html
(worth noting that i have them from china)
I am pulsing at the motor frequency x6 to get a single laser dot reflected of the mirrors.
The motor is receiving a PWM signal from an Arduino. The laser is receiving a 6x that frequency signal with a very small duty cycle.
For this I am using code that generates very precise pwn signals using ticks of the internal PWM clock. The signals are verified on my scope and are constant and in sync.
So far so good. I am getting my desired laser dot in the target area.
The problem is that the dot is wobbling back and forth.
I am on this project with a colleague who helped with all of this and made this video for him.
laser wobble
We cant figure out why that wobble happens.
These motors are used in laser printers and scanners and must spin with high precision.
We tried all kinds of things to make it steady. Hence the custom code for the PWM signals.
I have tried:
- using different signal sources in case there is a problem with aligning both signals
- hardware and software PWM's
- i hooked up an led to the laser signal and illuminated the spinning motor in a dark room. I could clearly see the edge of the mirror wobble in the same pattern as on the laser dot
- I blew air on the motor while doing the led test. That made the mirror wobble even more
- I own 3 different polygon motors of different brands. they all show the same behaviour
Is the motor broken? But all three of them?
Is it air turbulence? But that is also hard to believe since these motors sit in open spaces inside printers. If anything, then air turbulence would be worse in there.
Any tips on what that could be are well appreciated
This is the code we are using to create both PWM signals:
C++:
#include <TimerHelpers.h>
const byte intcheck = 8;
const byte timer1OutputA = 9;
const byte timer1OutputB = 10;
volatile uint8_t pulse_count = 0;
bool LED_STATE = true;
void setup() {
pinMode (timer1OutputA, OUTPUT);
pinMode (timer1OutputB, OUTPUT);
pinMode (intcheck, OUTPUT);
cli();
TCCR1A = 0; // Reset entire TCCR1A to 0
TCCR1B = 0; // Reset entire TCCR1B to 0
/*3. We enable compare match mode on register B*/
TIMSK1 |= B00000100; //Set OCIE1B to 1 so we enable compare match B
Timer1::setMode (15, Timer1:RESCALE_8, Timer1::CLEAR_A_ON_COMPARE | Timer1::CLEAR_B_ON_COMPARE);
OCR1A = 4000;
OCR1B = 5;
sei(); //Enable back the interrupts
} // end of setup
void loop() {}
ISR(TIMER1_COMPB_vect){
if (pulse_count < 2) {
pulse_count++;
} else {
pulse_count = 0;
PORTB ^= (1 << PB0); // toggle pin 8 (PB0)
}
}and this is temerhelpers.h:
C++:
/*
Timer Helpers library.
Devised and written by Nick Gammon.
Date: 21 March 2012
Version: 1.0
Licence: Released for public use.
See: http://www.gammon.com.au/forum/?id=11504
Example:
// set up Timer 1
TCNT1 = 0; // reset counter
OCR1A = 999; // compare A register value (1000 * clock speed)
// Mode 4: CTC, top = OCR1A
Timer1::setMode (4, Timer1::PRESCALE_1, Timer1::CLEAR_A_ON_COMPARE);
TIFR1 |= bit (OCF1A); // clear interrupt flag
TIMSK1 = bit (OCIE1A); // interrupt on Compare A Match
*/
#ifndef _TimerHelpers_h
#define _TimerHelpers_h
#if defined(ARDUINO) && ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif
/* ---------------------------------------------------------------
Timer 0 setup
--------------------------------------------------------------- */
namespace Timer0
{
// TCCR0A, TCCR0B
const byte Modes [8] [2] =
{
{ 0, 0 }, // 0: Normal, top = 0xFF
{ bit (WGM00), 0 }, // 1: PWM, Phase-correct, top = 0xFF
{ bit (WGM01), 0 }, // 2: CTC, top = OCR0A
{ bit (WGM00) | bit (WGM01), 0 }, // 3: Fast PWM, top = 0xFF
{ 0, bit (WGM02) }, // 4: Reserved
{ bit (WGM00), bit (WGM02) }, // 5: PWM, Phase-correct, top = OCR0A
{ bit (WGM01), bit (WGM02) }, // 6: Reserved
{ bit (WGM00) | bit (WGM01), bit (WGM02) }, // 7: Fast PWM, top = OCR0A
}; // end of Timer0::Modes
// Activation
// Note: T0 is pin 6, Arduino port: D4
enum { NO_CLOCK, PRESCALE_1, PRESCALE_8, PRESCALE_64, PRESCALE_256, PRESCALE_1024, T0_FALLING, T0_RISING };
// what ports to toggle on timer fire
enum { NO_PORT = 0,
// pin 12, Arduino port: D6
TOGGLE_A_ON_COMPARE = bit (COM0A0),
CLEAR_A_ON_COMPARE = bit (COM0A1),
SET_A_ON_COMPARE = bit (COM0A0) | bit (COM0A1),
// pin 11, Arduino port: D5
TOGGLE_B_ON_COMPARE = bit (COM0B0),
CLEAR_B_ON_COMPARE = bit (COM0B1),
SET_B_ON_COMPARE = bit (COM0B0) | bit (COM0B1),
};
// choose a timer mode, set which clock speed, and which port to toggle
void setMode (const byte mode, const byte clock, const byte port)
{
if (mode < 0 || mode > 7) // sanity check
return;
// reset existing flags
TCCR0A = 0;
TCCR0B = 0;
TCCR0A |= (Modes [mode] [0]) | port;
TCCR0B |= (Modes [mode] [1]) | clock;
} // end of Timer0::setMode
} // end of namespace Timer0
/* ---------------------------------------------------------------
Timer 1 setup
--------------------------------------------------------------- */
namespace Timer1
{
// TCCR1A, TCCR1B
const byte Modes [16] [2] =
{
{ 0, 0 }, // 0: Normal, top = 0xFFFF
{ bit (WGM10), 0 }, // 1: PWM, Phase-correct, 8 bit, top = 0xFF
{ bit (WGM11), 0 }, // 2: PWM, Phase-correct, 9 bit, top = 0x1FF
{ bit (WGM10) | bit (WGM11), 0 }, // 3: PWM, Phase-correct, 10 bit, top = 0x3FF
{ 0, bit (WGM12) }, // 4: CTC, top = OCR1A
{ bit (WGM10), bit (WGM12) }, // 5: Fast PWM, 8 bit, top = 0xFF
{ bit (WGM11), bit (WGM12) }, // 6: Fast PWM, 9 bit, top = 0x1FF
{ bit (WGM10) | bit (WGM11), bit (WGM12) }, // 7: Fast PWM, 10 bit, top = 0x3FF
{ 0, bit (WGM13) }, // 8: PWM, phase and frequency correct, top = ICR1
{ bit (WGM10), bit (WGM13) }, // 9: PWM, phase and frequency correct, top = OCR1A
{ bit (WGM11), bit (WGM13) }, // 10: PWM, phase correct, top = ICR1A
{ bit (WGM10) | bit (WGM11), bit (WGM13) }, // 11: PWM, phase correct, top = OCR1A
{ 0, bit (WGM12) | bit (WGM13) }, // 12: CTC, top = ICR1
{ bit (WGM10), bit (WGM12) | bit (WGM13) }, // 13: reserved
{ bit (WGM11), bit (WGM12) | bit (WGM13) }, // 14: Fast PWM, TOP = ICR1
{ bit (WGM10) | bit (WGM11), bit (WGM12) | bit (WGM13) }, // 15: Fast PWM, TOP = OCR1A
}; // end of Timer1::Modes
// Activation
// Note: T1 is pin 11, Arduino port: D5
enum { NO_CLOCK, PRESCALE_1, PRESCALE_8, PRESCALE_64, PRESCALE_256, PRESCALE_1024, T1_FALLING, T1_RISING };
// what ports to toggle on timer fire
enum { NO_PORT = 0,
// pin 15, Arduino port: D9
TOGGLE_A_ON_COMPARE = bit (COM1A0),
CLEAR_A_ON_COMPARE = bit (COM1A1),
SET_A_ON_COMPARE = bit (COM1A0) | bit (COM1A1),
// pin 16, Arduino port: D10
TOGGLE_B_ON_COMPARE = bit (COM1B0),
CLEAR_B_ON_COMPARE = bit (COM1B1),
SET_B_ON_COMPARE = bit (COM1B0) | bit (COM1B1),
};
// choose a timer mode, set which clock speed, and which port to toggle
void setMode (const byte mode, const byte clock, const byte port)
{
if (mode < 0 || mode > 15) // sanity check
return;
// reset existing flags
TCCR1A = 0;
TCCR1B = 0;
TCCR1A |= (Modes [mode] [0]) | port;
TCCR1B |= (Modes [mode] [1]) | clock;
} // end of Timer1::setMode
} // end of namespace Timer1
/* ---------------------------------------------------------------
Timer 2 setup
--------------------------------------------------------------- */
namespace Timer2
{
// TCCR2A, TCCR2B
const byte Modes [8] [2] =
{
{ 0, 0 }, // 0: Normal, top = 0xFF
{ bit (WGM20), 0 }, // 1: PWM, Phase-correct, top = 0xFF
{ bit (WGM21), 0 }, // 2: CTC, top = OCR2A
{ bit (WGM20) | bit (WGM21), 0 }, // 3: Fast PWM, top = 0xFF
{ 0, bit (WGM22) }, // 4: Reserved
{ bit (WGM20), bit (WGM22) }, // 5: PWM, Phase-correct, top = OCR2A
{ bit (WGM21), bit (WGM22) }, // 6: Reserved
{ bit (WGM20) | bit (WGM21), bit (WGM22) }, // 7: Fast PWM, top = OCR2A
}; // end of Timer2::Modes
// Activation
enum { NO_CLOCK, PRESCALE_1, PRESCALE_8, PRESCALE_32, PRESCALE_64, PRESCALE_128, PRESCALE_256, PRESCALE_1024 };
// what ports to toggle on timer fire
enum { NO_PORT = 0,
// pin 17, Arduino port: D11
TOGGLE_A_ON_COMPARE = bit (COM2A0),
CLEAR_A_ON_COMPARE = bit (COM2A1),
SET_A_ON_COMPARE = bit (COM2A0) | bit (COM2A1),
// pin 5, Arduino port: D3
TOGGLE_B_ON_COMPARE = bit (COM2B0),
CLEAR_B_ON_COMPARE = bit (COM2B1),
SET_B_ON_COMPARE = bit (COM2B0) | bit (COM2B1),
};
// choose a timer mode, set which clock speed, and which port to toggle
void setMode (const byte mode, const byte clock, const byte port)
{
if (mode < 0 || mode > 7) // sanity check
return;
// reset existing flags
TCCR2A = 0;
TCCR2B = 0;
TCCR2A |= (Modes [mode] [0]) | port;
TCCR2B |= (Modes [mode] [1]) | clock;
} // end of Timer2::setMode
} // end of namespace Timer2
#endif
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