Hey Guys,
I've been working on developing a current controller for a DC Motor for quite some time now and I keep coming up to this same stumbling block.
I'm using an integrated H-bridge driver, I've tried the LMD18200t, and now im trying the L6205 from ST. In either case I am getting the same results.
I've tried both the sign/magnitude and also lock/antiphase methods for switching but I'm having difficulties because in my application I need to eliminate the feeling of damping torque caused by the motors back-emf.
Basically, when the motor is idle, and you back-drive the shaft with your hand, you feel a shaft-velocity dependent torque on the shaft opposing your hand. I want to eliminate this feeling all together.
On both the LMD18200t and L6205 for the OFF state it is possible to switch all of the mosfets off (using the enable logic input), and this will allow the motor to free-wheel in the off state. I've tried this, and the back-emf damping is no longer present.. although now the relationship between pwm-duty cycle and motor voltage seems to be thrown out of whack. I've found that I cant really start to see any significant voltage until close to 3/4 duty cycle, and in that last 1/4 duty cycle I get all the voltage increase.
I'm puzzled, especially since I've reproduced the exact same problem on two completely different parts.
My next test will be using a current sense resistor, which I've just tried on the high side supply.. but this measurement seems to be noisy.
Im wondering if I can use one of the two original control schemes, along with a current sensing scheme to actively eliminate the feeling of back-emf damping on the motor shaft?
cheers,
Ryan
I've been working on developing a current controller for a DC Motor for quite some time now and I keep coming up to this same stumbling block.
I'm using an integrated H-bridge driver, I've tried the LMD18200t, and now im trying the L6205 from ST. In either case I am getting the same results.
I've tried both the sign/magnitude and also lock/antiphase methods for switching but I'm having difficulties because in my application I need to eliminate the feeling of damping torque caused by the motors back-emf.
Basically, when the motor is idle, and you back-drive the shaft with your hand, you feel a shaft-velocity dependent torque on the shaft opposing your hand. I want to eliminate this feeling all together.
On both the LMD18200t and L6205 for the OFF state it is possible to switch all of the mosfets off (using the enable logic input), and this will allow the motor to free-wheel in the off state. I've tried this, and the back-emf damping is no longer present.. although now the relationship between pwm-duty cycle and motor voltage seems to be thrown out of whack. I've found that I cant really start to see any significant voltage until close to 3/4 duty cycle, and in that last 1/4 duty cycle I get all the voltage increase.
I'm puzzled, especially since I've reproduced the exact same problem on two completely different parts.
My next test will be using a current sense resistor, which I've just tried on the high side supply.. but this measurement seems to be noisy.
Im wondering if I can use one of the two original control schemes, along with a current sensing scheme to actively eliminate the feeling of back-emf damping on the motor shaft?
cheers,
Ryan