Re: [CAD_CAM_EDM_DRO] steppers or servo?

Terry Ackland wrote:

> Hi,
> Computer printers use stepper motors and they run forever with
> incredible accuracy. A hobby nc machine will also have the same
> repeatability as long the motors are not forced into missed steps,
> right?
> Servos can also be forced into missed steps so the advantage over
> steppers must just be the extra speed to return to the home
> position?

A true servo system can NOT be forces into missing 'steps' because there
aren't
any 'steps', as such. Since the encoder counters generally are 24-bit
hardware
counters, they can handle a large range of motion with high resolution,
and always
keep an absolute position count in the hardware. The only way a true
servo
system could lose position is if the computer was turned off or the
encoders
were disconnected from the computer or the machine.

By a true servo system, I mean a system where the shaft or linear
encoders
are connected to the CNC computer, and a velocity command is sent to
the servo amp. The mini-servo systems that take step and direction
pulses and run servo motors can lose position if the CNC computer is
not also reading the encoders.

Jon