Controlling Servo Drive from MCU

[UroBoros]

I have a 1.5Kw servo with its drive. The drive has RS232 port , but the Chinese maker says it is for config only. I need to vary the speed of this servo based on a feed back , closed loop control. As from the documentation the only way to vary the speed at run time is by changing the voltage applied to a pin. That pin can accept -10 to +10V so that it will change its speed from max anticlockwise to max clockwise.
Please confirm weather my understanding is correct as the general case with servo drives!

Considering that the only possible way available to vary speed is by changing the voltage in a control pin, which is the ideal method to do this from a PIC MCU. Digital potentiometer chip I have tried but not giving enough resolution.
Please suggest!

 

[KlausST]

Hi,

Possible solutions:
* PWM - CMOS switch - Low pass filter
* DAC - opamp

Hope this helps
Klaus

 

[Debasis Swain]

Dear friend,
for your kind information a servo motor can only control by pwm signal, it may be from mcu or any other circuit from which you may generate a different type of pwm by which you can control the servo.

 

[UroBoros]

Dear friend,
for your kind information a servo motor can only control by pwm signal, it may be from mcu or any other circuit from which you may generate a different type of pwm by which you can control the servo.

Please Read the post carefully my friend, I am talking about controlling the drive, not servo motor!
The PWM you mentioning is taken care of by the Drive. My problem is how to convey to the Drive my 'intentions'.

Thanks KlausST for the info.

Possible solutions:
* PWM - CMOS switch - Low pass filter
* DAC - opamp

PWM and low pass filter I understood the purpose, but why the CMOS switch?
Also can you suggest a easily available DAC for this purpose?
Thanks again.

 

[KlausST]

Hi,

CMOS switch:
I did recommend because you need -10V to +10V if i understood right.
The PWM output of a ucontroller usually can output 0V to VCC (wich is 3.3V or 5V)

My idea was to use the PWM to control an SPDT switch. NC connected to -10V and NO connected to +10V. The COM output to an lowpassfilter.
With this you are able to generate -10 to +10 V control voltage.

Hint:
often CMOS switch have an enable input. You can use this to stop the motor - you simply add a resistor from COM to GND.
With a disabled switch COM is high impedance and the resistor pulls the signal 0V.

Hope this helps
Klaus