Re: [CAD_CAM_EDM_DRO] Re: Servo controllers for table top machines.

> It sounds like a micro stepping system will provide the same
> repeatability and precision as a Servo system like the one from
> camtronics. Then why are there so many companies saying that servo
> will be a better system?
>

Remember a stepper motor can only be guaranteed to be within +/- 2 full
steps of the desired position. If you are using 10x microstepping this
means that it is within +/- 20 counts. A stepper motor is basically an
iron core that follows a magnetic field. Magnetic fields are not rigid
so any load on the motor will make it deflect from the commanded
position. Servos electronically compensate for this so under steady
state conditions they are usually within a couple of encoder counts.
Under dynamic load (acceleration/deceleration) they can have more error
depending on the motor tuning and how aggressive the acceleration is.

If you need very high resolution you can increase the encoder
resolution. However this can limit your top speed.

> If I go with the camtronics servo control with the MCG NEMA23 frame
> brush type servo motors, will I still have to use a reduction pulley
> or can that be bolted directly to the ball screw like my current system?
>

Servos and steppers have different characteristics so it can be
difficult to directly compare them. If you are cutting at high speed
(wood routing for instance) then you need a servo with a peak torque
rating at least equal to a stepper's holding torque. If you are cutting
at low speed with high speed rapids (metal cutting for instance) then
you need a bigger servo.

If the servo can't deliver enough torque you need to gear it down or get
a bigger motor.

> The servo system from Techno bolts the servo motors directly to the
> ball screw with out a reduction pulley. The only thing is they have a
> brake on the Z-axis.
>

The brake is to stop the Z axis falling under it's own weight when power
is removed. Steppers have a fairly high holding torque with power
removed. Servos are very free-running with power removed.

Les