Re: Help a confused newbie out please

Hi Jerry, Jim,

On the subject of "loosing position/counts", if the stepper(s) are
stopped abruptly with out deceleration, they WILL loose position (the
rotor will continue to rotate a short distance, without requiring any
steps). Servo systems have an encoder for feedback, therefore this is
not a problem for them). If the stepper system is moving at or near the
"startup" speed, then no steps should be lost (gained?), as the rotor
CAN stop instantly.

So, One might want a limit to decelerate to avoid loss of position
(that's where the roller microswitches come in).

E-STOP should probably stop as soon as possible, as damage/injury is is
imminent!

Home switches are "passed up", then the carriage backs up and takes a
SLOW move on the switch for ACCURATE location.

Now where to put the limit/home switches on my Sherline...

FWIW

Alan KM6VV



Carol & Jerry Jankura wrote:

>
> Hi, Jim:
>
> The E-Stop is intended to be used by an operator to stop the machine when
> the operator sees something wrong. It could be that the carriage has bumped
> into a hard limit, or it could be that the oprator has caught his/her hand
> in the machine. The actions due to the E-Stop should stop all motion and put
> the machine in a 'safe' condition.
>
> The limit switch is there only to detect that the carriage (or something)
> has reached the end of travel. It will typically stop the motors.
>
> Either system can maintain position information, depending on how the
> control is designed.
>
> -- Jerry
>
> |I thought that a limit stop was the same function as an Estop
> |condition for the controller program. I didnt know that they were
> |2 seperate things.Told ya I was a newbie!
> |So an Estop will cause you to lose position sync,and it stops
> |movement abruptly?
> |Does a limit stop cause a position sync loss also?How does it stop
> |the travel.....abrubptly also?(Im using steppers until I learn
> |more, then Ill advance to servos)
>
> Place them near the end of physical travel, but allow some travel for the
> motors to slow and stop, as there may not be a brake in the system.
>
> |I had planned on using microswitches with rollers on them, that
> |would act as a limit stop as the table/saddle swept them. I just
> |didnt know where to place them(ie, before the actual travel limit
> |or at the end of travel)
>