Re: Pulsing circut

--- In CAD_CAM_EDM_DRO@yahoogroups.com, David Paulson <stlspply@s...>
wrote:

> Hi
> I am in the process of constructing a rotary table for use with my
> welding robot. I have a large (36" dia) cnc rotary table that I

had

> purchased on ebay. It has a 140v DC servo mounted on it for the
> movement. I have purchased a AMC brush type dc servo amp that has

a

> step (com, +10v) and direction (com, +10v) pins. My idea was to
> program a plc with the required foot switch and two limit switches

(one

> for each position of the table) to control the servo amp and

communicate

> with the robot controller. I chose to power the servo though the

servo

> amp because when power is removed from the step pin, the motor will

stop

> instantly, but the problem is the speed at which the table turns.

The

> limit switches do not accurately activate at the same place each

time.

> So my next idea is to install another set of limit switches approx.

1

> 1/2" before the position limit switch and to send a pulsing circuit

to

> the servo amp to effectively slowing down the motor so that the

position

> limit switch can more accurately sensed. Does this make sense to
> anyone? So my question is, does anyone know how to build such a
> circuit, possibly using a pot to adjust the frequency of a +10v

pulse.

> Thanks
>
> David Paulson

build an AND gate so that the limit switch stops the step pulses. a
simple transistor and two diodes with both anodes tied to the base of
the transistor through 4.7K limit resistors will work with the logic
so that the collector goes low only when both of the cathodes are
high. Either cathode low means no steps. The limit then is
connected to one cathode so that on activation it goes low. You will
need a bypass switch to be able to move the table off the limits.

A really good wide range pulse generator using a single pot for
frequency can be built using a CMOS 4060 PLL chip. I have an old
schematic somewhere that uses a joystick to control a two axis
pulsing engine with a wide pulse range. I can dig it out if you are
interested. It would be easy to build in an inhibit that stops
pulses when you hit a limit. With a foot reostat you could control
speed. If you could rig a foot "joystick" you could control both
speed and direction.

Tom C